Table of contents

The porous carbons derived from bio-mass precursors for energy storage devices have

been gained increased research attention due to their cost effectiveness, easy way to fabrication, ecofriendly nature and more sustainability. Carbon derived from biomass is more favorable electrode material for supercapacitor. In the recent work we successfully prepared interconnected nanosheets porous carbon from withered rose by facile, post treatment, pre carbonization, acid washing and activation process. This rose-derived active carbon nanosheets (RDPC) display a high specific surface area (1980m2g-1) with a small pores after activation process. RDPC exhibit the electrochemical properties of the prepared porous carbon were analyzed by 3-electrode configuration with 6 M KOH electrolyte. It is implies that the porous carbon exhibited the high specific capacitances of 350 F g-1 at 1 A g-1, and 165 F g-1 at 150 A g-1. Besides, the porous carbon can be achieved an excellent long-cycling life with only loss 2.7% of its initial capacitance over 1,20,000 cycles even at 150 A g-1. The observed very attractive electrochemical behavior of the new biomass porous carbon derived from tea waste will be a competitive candidate as cathode material in the development of high-performance and green supercapacitor for advanced energy storage devices.

Figure 1

Carbon with different structures and properties is almost indispensable as active or assisting materials in battery devices. In this presentation, I will share several examples of controlling the structure and surface chemistry of carbon materials for active anode materials, surface coating layers, and conducive and/or mechanical frameworks in different kinds of battery applications. Si-based anodes for Li-ion batteries, Na-ion batteries and Li-S batteries will be discussed.

It's well known that the Li-O₂ battery can achieve theoretically¹ ten times as much energy density (5200Wh/kg) as Li-ion battery but often limited in reality on the capacity and the cycling. In this system, the carbon cathode provides merely a framework for the lithium peroxide deposition but is not an active material. The dissolved oxygen in the electrolyte is indeed the active material. In other words, the capacity depends on the porosity and the framework architecture. Our previous X-ray tomographic study² pointed out that a sparse structure is needed to increase the capacity by impeding the pore clogging and oxygen depletion. The conventional fabrication by evaporating the solvent of a slurry can only provide ~20% porosity which is insignificant. Other templating fabrications^3,4 are often reported in the literature, but procedures are tedious. To fabricate sparse and self-standing cathode with the multi-wall carbon nanotubes (MWCNTs), we propose a facile and scalable two steps Buchner approach.

The MWCNTs are firstly dispersed in a solvent by sonification. A direct filtration with the separator of a battery can omit a stacking step in the battery assembling (Figure 1). Preceded by a drying process, the cathode is then investigated in the overall cell for electrochemical performance and cyclability. The data of X-ray nano-Computed Tomography acquired in APS synchrotron (ID32) shows that the material is highly porous and the pores are fully filled with the discharge product Li₂O₂ which conducts to a capacity improvement. Impedance is utilized alongside with tomography data for a complementary understanding of the dominance between lithium ion and oxygen depletion during the discharge.

The self-standing and flexible properties of such cathode even without polymer binder are beneficial for industrial application. We demonstrate the possibility of loading other particles with our approach. A gain of specific surface area for the deposition of lithium peroxide can be obtained with the loading at a price of the mechanical property detriment. Thereby, several percentages of loading are studied to obtain the best trade-off. Besides, bared carbon-nanotube framework with loaded particle trends to loss the structural stability. A sandwich-like structure is hence investigated for the efficiency of the particle confinement.

Finally, our approach is highly eco-friendly. The solvent for nanotube dispersion can be reused after the filtration. And the aged cathode is entirely recyclable by proceeding a low-cost acid retreatment then ultrasonic re-dispersion. The impact of the recycling in terms of electrochemistry and pressure evolution have also been studied.

Figure 1. (a) image of the homogeneous laid out cathode in a Buchner (b) SEM image of the intersection separator and cathode and (c) sandwich structure (d) electrochemical curve with pressure evolution Reference:

(1) Abraham, K. M. A Polymer Electrolyte-Based Rechargeable Lithium/Oxygen Battery. Journal of The Electrochemical Society1996, 143 (1), 1. https://doi.org/10.1149/1.1836378.

(2) Su, Z.; De Andrade, V.; Cretu, S.; Yin, Y.; Wojcik, Michael. J.; Franco, Alejandro. A.; Demortière, A. X-Ray Nano-Computed Tomography in Zernike Phase Contrast for Study 3D Morphology of Li-O2 Battery Electrode. ACS Applied Energy Materials (submitted)

(3) Cho, S. A.; Jang, Y. J.; Lim, H.-D.; Lee, J.-E.; Jang, Y. H.; Nguyen, T.-T. H.; Mota, F. M.; Fenning, D. P.; Kang, K.; Shao-Horn, Y.; et al. Hierarchical Porous Carbonized Co ₃ O ₄ Inverse Opals via Combined Block Copolymer and Colloid Templating as Bifunctional Electrocatalysts in Li-O ₂ Battery. Advanced Energy Materials2017, 7 (21), 1700391. https://doi.org/10.1002/aenm.201700391.

(4) Gaya, C.; Yin, Y.; Torayev, A.; Mammeri, Y.; Franco, A. A. Investigation of Bi-Porous Electrodes for Lithium Oxygen Batteries. Electrochimica Acta2018, 279, 118–127. https://doi.org/10.1016/j.electacta.2018.05.056.

Figure 1

Increasing the energy storage capability of lithium-ion batteries necessitates maximization of their areal capacity. This requires thick electrodes performing at near-theoretical specific capacity. However, achievable electrode thicknesses are restricted by mechanical instabilities, with high-thickness performance limited by the attainable electrode conductivity. Here we show that forming a segregated network composite of carbon nanotubes with a range of lithium storage materials (for example, silicon, graphite and metal oxide particles) suppresses mechanical instabilities by toughening the composite, allowing the fabrication of high-performance electrodes with thicknesses of up to 800 μm. Such composite electrodes display conductivities up to 1 × 10⁴ S m⁻¹ and low charge-transfer resistances, allowing fast charge-delivery and enabling near-theoretical specific capacities, even for thick electrodes. The combination of high thickness and specific capacity leads to areal capacities of up to 45 and 30 mAh cm⁻² for anodes and cathodes, respectively. Combining optimized composite anodes and cathodes yields full cells with state-of-the-art areal capacities (29 mAh cm⁻²) and specific/volumetric energies (480 Wh kg⁻¹ and 1,600 Wh l⁻¹).

However, such thick electrode might be expected to show poor rate performance. Optimisation of the combination of areal capacity and rate performance would be simplified if a simple mechanistic model linked both parameters to electrode properties. Here we demonstrate an equation which can fit capacity versus rate data, outputting three parameters which fully describe rate performance. Most important is the characteristic time associated with charge/discharge which can be linked by a second equation to physical electrode/electrolyte parameters via various rate-limiting processes. We fit these equations to ~200 data sets, deriving parameters such as diffusion coefficients or electrolyte conductivities. It is possible to show which rate-limiting processes are dominant in a given situation, facilitating rational design and cell optimisation. In addition, this model predicts the upper speed limit for lithium/sodium ion batteries, yielding a value that is consistent with the fastest electrodes in the literature. We show that this equation completely describes much experimental rate data.

Secondary energy storage technologies based on sodium ions are an important emerging alternative to lithium ion batteries (LIBs). Sodium is less expensive than lithium, with its supplies being much wider and more democratically distributed throughout the globe. There are fundamental physical differences between Na and Li, and it is clear the knowledge available from extensive research on LIBs does not translate to sodium. However, the understanding of Na-based systems is at their infancy, and their complexities are just beginning to be understood. In this talk, we theoretically investigated the possibility of using phosphorus-doped (P-doped) graphene as an anode material in sodium ion batteries (NIBs). We reveal some fundamental physical properties of sodium adsorption on P-doped graphene by calculating formation and adsorption energies, voltage vs. capacity curves, migration for Na transport, and electron density of states and mobility. Our calculations suggest that Na adsorption on the same side of protrudent P is the preferred configuration for application in NIBs. This particular configuration possesses very large Na capacity (~582 mAh/g). More importantly, Na has to cross a diffusion barrier (~0.3 eV) and it diffuses in a zigzag path on the P-doped structures due to the presence of protrudent P with larger atomic size compared with the size of a carbon. We will also present electronic movements and accumulations during sodiation. Though carrier mobility may be not as fast as in metals or pristine graphene because P-doped graphene with Na adsorbed on it becomes a semiconductor, the calculated carrier mobility is still significantly large with the order of 10³ to 10⁵ cm²/V/s. Lastly, we will discuss the guidelines for the efficient design of P-doped graphene as a promising anode for NIBs.

Heteroatom-doped graphene materials show high capacity as Li-ion battery anodes. However, the Li+ reduction potential in doped graphene anodes varies drastically during charging/discharging, which adversely affects battery performance. The varying reduction potential is conjectured to result from graphene sheets aggregating during electrode preparation into a disordered graphite structure, which demonstrate a similar reduction potential profile. To test this conjecture we measured the disorder during charging/discharging via in situ x-ray diffraction. We find that the doped graphene interlayer spacing irreversibly increases during the first discharge prior to solid electrolyte interphase formation, and commensurate with this phenomena we find an increase in double-layer capacitance, suggesting an increase in surface area. These results imply an increase in disorder during the first discharge, which supports the conjecture that doped graphene batteries resemble disordered graphite. However, a significant disordering occurs during the first discharge and not necessarily during electrode preparation.

Growing environmental concerns linked with global energy demands have increased the need for sustainable, reliable and portable energy supply that can be delivered from energy conversion to energy storage. Although some emerging electrocatalysts can potentially compete with commercial electrocatalysts in terms of cost per unit kWh when using low-cost precursors to create them, research efforts are still mainly focusing on performance rather than cost. It is expected that flexible energy storage devices with multifunctionalities would spearhead the power management of future energy devices, which requires engineering solutions of volume and weight reduction. Nanocomposites that offer simultaneous energy conversion and storage capabilities with mechanical load bearing are promising candidates to provide these desired functionalities in electrochemical devices. Utilizing hierarchical porous polymers with combined properties of light weight, flexibility and absorption capacity offers numerous possibilities for the development and utilization of nanocomposites in applications ranging from electronics, aerospace, military to transportation where rapid or stored burst of energy is required for peak power, backup power and load levelling to achieve improved efficiency and reliability.

In this work, iron oxide nanoparticles encapsulated in graphitic carbon nitride shells (Fe_x-NC) were grown on interconnected, macroscopic carbon scaffold after dip coating followed by carbonization to attain multifunctional nanocomposites. The resulting composites based on the graphitic carbon nitride base possess combined properties of superb structural flexibility, high strength to weight ratio and mechanical stability. The Fe_x-NC nanocomposites were tested for energy conversion and storage, to take advantage of their porous graphitic carbon nitride features which would be beneficial for optimal ion transport to iron oxide nanoparticles. We have found that the resulting graphitic carbon nitride shells prevented direct contact between iron oxide nanoparticles and acidic electrolyte (H₂SO₄), so that improved efficiency, stability and corrosion resistance were achieved. They also exhibit excellent electrochemical performances with overpotentials of 191 mV to reach current density of 10 mA/cm² for hydrogen evolution reaction. In addition to demonstrating excellent specific capacitance, these nanocomposites also possess good stability after 8 hours of testing. The results demonstrate that the physicochemical properties of multifunctional 3D foams developed from simultaneous carbonization and dip coating of polymeric templates can be used as an excellent base to host a variety of nanoparticles to create composite electrocatalysts and be further exploited for future energy and environmental technologies.

We will discuss various carobn nanostructures and their derivates for zinc ion storage, for example, a zinc ion capacitor based on carbon nanotubes. In addition, prussian blue analogue (PBA)-type metal hexacyanoferrates have been considered as significant cathode materials for aqueous rechargeable zinc batteries (ZBs) due to the open face centered cubic framework, multiple active sites, and environmental benign. However, these PBA-type cathodes, such as cyanogroup iron hexacyanoferrate (FeHCF), suffer from ephemeral lifespan (≤1000 cycles), inferior rate capability (1A g^-1), and low operating voltage (ca. 1.2 V). This is because the redox active sites of multivalent iron (Fe(III/II)), which dominates its electrochemical activities, can only be very limited activated and thus utilized. The limited activity is attributed to the spatial resistance caused by the compact cooperation interaction between Fe and the surrounded six cyanogroup per unit, and the inferior conductivity. In this paper, surprisingly, we found high-voltage-scanning can effectively activate the C-coordinated Fe (redox active sites) in FeHCF cathode in ZBs. The activation spurred the increase of capacity at a high operating voltage plateau of ca. 1.5 V. Thanks to this activation, the Zn-FeHCF hybrid-ion battery achieved a record-breaking cycling performance of 5000 (82% capacity retention) and 10000 cycles (73% capacity retention), respectively, together with a superior rate capability of maintaining 53.2% capacity at super-high current density of 8 A g^-1 (ca. 97 C).

Figure 1

The synthesis of diamino-aryl-1,4,5,8-naphtalenetetra-carboxylic diimide molecule (NTCDA-(aryl-NH₂)₂) was reported. This molecule was characterized by elemental analysis, SEM, IR and TGA. A organic Li-ion electrode with NTCDA-(aryl-NH₂)₂ as active material was tested and a reversible behavior was observed with a multiple electrons process delivering about 100 mAh.g^-1 at an average potential of 2.45 V vs. Li/Li⁺. In parallel, the diazotization study of this molecule was investigated with a three-electrode assembly. Then, the electrochemical reduction of freshly formed NTCDA-(aryl-N₂⁺)₂ ions was followed by cyclic voltammetry experiments. An irreversible cathodic wave at around 0.0 V vs. Ag/AgNO₃ that is associated to the reduction of the in-situ generated NTCDA-(aryl-N₂⁺)₂ ions was observed. The blocking effect of the grafted layer deposited on the glassy carbon surface was verified with ferrocene as a redox probe. Finally, the immobilization of this molecule on Ketjen black carbon powder by spontaneous reduction of freshly formed NTCDA-(aryl-N₂⁺)₂ ions was realized in a one-pot reaction. The redox-active carbon with a loading of grafted groups estimated between 26.4 and 36.7 wt. %, depending of the method of modification, cycled at high rate for thousands of cycles.

With the highest theoretical capacity and lowest electrochemical potential, lithium (Li) metal is considered as the ideal anode for Li-ion based battery.^[1] Unfortunately, the practical application of Li metal battery has been hindered by the growth of dendritic crystals, infinite volume changes, and high reactivity of lithium metal during battery charging and discharging.^[2] Despite previous progress, it is still highly needed to develop efficient lithium host to solve aforementioned problems.

Electrochemical water splitting, namely hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been under intense research.^[3] This is because hydrogen is the cleanest fuel and thus considered as the major fuel for future use. Electrochemical HER and OER are sluggish which requires the use of catalysts to boost the reaction rate. However, the best catalysts for HER and OER are still based on noble metals such as Pt and Ir/Ru, which are too expensive to be afforded widely. Developing low-cost, earth-abundant, highly efficient and stable bifunctional catalyst for overall water splitting is highly required but remains challenging.^[4]

In the past decades, hierarchical arrays have been widely used for energy storage and conversion devices due to the highly exposed surface, fast transportation of ions and matter, intimate contact between current collector and active materials.^[5-6] Nevertheless, the report on hierarchical carbon arrays remains rare. Herein, we develope a general method for coating of hierarchical carbon nanosheet arrays on substrates for lithium metal battery and water splitting. For the lithium metal battery part, hierarchical nanosheet arrays are grown onto Cu foil by the self-assembly of polymer, which was converted to carbon arrays after carbonization. Owing to the hierarchical carbon arrays, highly exposed surface area, and electroactive nitrogen dopants, the hierarchical carbon-coated Cu foil can facilitate the growth of horizontal lithium crystals, inhibiting lithium dendrites growth, and thus manifesting high Coulombic efficiency of >98% in ether electrolyte and >90% in carbonate electrolyte as well as long-cycling stability for 500 cycles. As for water splitting, hierarchical polymer nanosheets are grown on Ni-Mo-containing arrays which grow onto Ni foam, which was converted by carburization to Ni-Mo₂C-carbon hybrid arrays with high activity and stability for both HER and OER. The catalyst, acting as both cathode and anode, requires only 1.61 V to generate a current density of 10 mA cm^-2 towards overall water splitting and the activity can be maintained for more than 150 h.

References:

(1) Lin, D.; Liu, Y.; Cui, Y. Nature Nanotechnology 2017, 12, 194.

(2) Xie, J.; Christensen, J.; Cui, Y, et al.Science Advances 2018, 4.

(3) Zhu, C.; Zhang, H.; Fan, H. J. et al Adv. Mater. 2018, 30, 1705516.

(4) Zhu, Y. P.; Ma, T. Y.; Jaroniec, M.; Qiao, S. Z., Angew. Chem. Int. Ed. 2017, 56, 1324-1328.

(5) Fang, M.; Dong, G. F.; Wei, R. J.; Ho, J. C. Adv. Energy Mater. 2017, 7, 1700559

(6) Zhou, L. M.; Zhang, K.; Hu, Z.; Tao, Z. L.; Mai, L. Q.; Kang, Y. M.; Chou, S. L.; Chen, J. Adv. Energy Mater. 2018, 8, 1701415.

Figure 1

The two-dimensional nanostructures are attractive materials for energy storage electrode materials due to extensive intercalation of ions. The two dimensional layered structure with suitable van-der-Waals gap along with multilayered arrangement is favorable to enhance the intercalation of ions. We report an innovative architecture composed of two dimensional multilayer delta-MnO₂ nanosheets grown on carbon nanoparticles (CNP) by simple, template-free, low temperature chemical method. The electrochemical kinematics investigation has been done through impedance spectroscopic analysis and scan rate dependent storage mechanism as effect of increasing temperature. The specific capacitance elevated to 321 F.g^-1 as temperature improves upto 70^oC at 2 mV.s^-1 which is almost double increment in the capacitance and four times enhancement in the energy density. However, the stability is compromised only 25% up to 6000 cycles at 5 A.g^-1 current density. The temperature increment is boosting ionic conductivity, enlarging the van-der-Waal gap and increasing charge transfer, simultaneously enrich intercalations of Na⁺ ions that initiate tremendous boost in energy storage. Thus a 3D architecture of multilayerd delta-MnO₂ nanosheets exhibits high-temperature superior performance pseudocapacitors with low life spam by compensating which is highly noteworthy.

Lithium-ion battery (LIB) electrode performance is directly related to charge movement within the electrode material. Improving electrode kinetics involves lowering the internal resistance which may be achieved through 1) nanosizing the active material to decrease the lithium-ion diffusion path; 2) using highly conductive additives; and 3) homogeneous microstructuring to form an effective percolation network for electron and ion conductive pathways. Among these highly conductive additives is the 2D graphene, or reduced graphene oxide (rGO, so-called due to its synthetic pathway). Which, thanks to its few-layers of densely packed sp2 hybridized carbon atoms with delocalized electrons, has excellent mechanical properties and electronic conductivity. However, achieving the desired homogeneity between active and conductive components is a challenge for the conventional tape-casting technique – particularly when nanosized and/or 2D nanomaterials are involved. The nano and 2D nature of the materials will present rheological challenges during the casting of the electrode slurry and result in mesoscale aggregation which is a property that triggers, or further accelerates, battery degradation. Thus, the benefits of nanosizing and using graphene are lost.

Electrophoretic deposition (EPD) is a novel electrocoating technique capable of assembling coatings from a stable suspension through the application of an electric field. It is well accepted that EPD has excellent self-assembling capabilities and herein lies its advantage to being used to fabricate composite lithium-ion electrodes. EPD provides a simplified coating technique with short process times. Moreover, the versatility of the suspension also allows EPD to be potentially environmentally friendly – a property not available to the tape casting technique due to its use of the highly toxic N-Methyl-2-pyrrolidone solvent. The challenge of electrophoretically depositing graphene is that a stable graphene suspension is difficult to form due its strong propensity for interaction between sheets. Thus, this problem may be sidestepped by using graphene oxide (GO) which is a functionalized graphene derivative. The functional groups located on the graphene surface provide electrostatic repulsion which prevents aggregation during dispersion and also allows the use of more polar solvents. With this in mind, our McGill HydroMET group has successfully used EPD to fabricate binder-free composite electrodes with rGO as conductive material and lithium titanate spinel (Li₄Ti₅O₁₂, LTO) or titanium niobate (TiNb₂O₇, TNO) as the nanosized active material. This was accomplished through co-deposition of conductive and, in the case of LTO, active material precursor followed by high temperature annealing to induce transformation of GO to rGO (and transformation of LTO precursor to the final spinel LTO) (Uceda, M., Chiu, H.-C., Gauvin, R., Zaghib, K., Demopoulos, G. P. (in press) Electrophoretically co-deposited Li₄Ti₅O₁₂/reduced graphene oxide nanolayered composites for high-performance battery application. Energy Storage Materials). Both types EPD systems are then compared to conventionally casted electrodes through electrochemical testing and physical characterization. In both cases, EPD is shown to provide superior homogeneity which results in improved electrode kinetics and battery performance.

Acknowledgments: This research was supported by Hydro-Quebec/NSERC grants and the McGill Sustainability Systems Initiative (MSSI).

Reducing charge-discharge overpotential is of great significance to enhance the efficiency and cyclability of Li−O2 batteries. Here we successfully achieve dramatically reduced charge overpotential (0.4 V) via a rational design of cathode architecture, which features highly uniform Pt and Pt3Co nanocrystals embedding within nitrogen-doped cobalt@graphene heterostructures. Because of the improvement on the catalytic efficiency for optimizing the electrical and dynamic properties, the cathode design enables promising electrochemical performance. More importantly, the results reveal different overpotential prompted by different structural evolution of bulk Li2O2, which depends on the Pt modification approach (surface-coating and bulk-doping). This dependence is found to be attributed to the influence of Pt nanocomponents and their dispersion on the formation and decomposition mechanism of Li2O2. Density functional theory calculations provide mechanistic insights into the promotional effect of Pt and Pt3Co on the reduction of the charge overpotential. Finally, an inner relationship between overpotential and electrochemical kinetics is proposed.

Graphene belongs to an emerging class of ultrathin carbon membrane materials with a high specific surface area, chemical stability, and high electrical and thermal conductivities. Owing to these intrinsic physicochemical characteristics, graphene has been extensively investigated for widespread applications in nanodevices, sensors, catalysis, energy storage systems, and biomedicine as an alternative to porous carbon. In particular, graphene has received increasing attention as an electrode material for electrical double-layer capacitors (EDLCs) due to its high specific surface area and high intrinsic electrical conductivity. Recently, there have been tremendous achievements for improving the gravimetric capacitance of graphene.

However, due to the 2D nature of the graphene sheet, graphene can easily restack to form lamellar microstructures on the current collector during the electrode fabrication process. The restacking of the graphene sheets may greatly reduce the utilization of the electrode material and limit the electron and mass transport at the interface of electrode, which as a result leads to decreased capacitor performance.

Taking these points into consideration, one strategy for preventing the restacking of graphene sheets is to use CNTs as nanospacers, given their high electrical pathways and large surface area. Recently, several approaches have been reported for fabricating graphene/CNT composites. The most popular approach for fabricating graphene/CNT composites is the preparation of an aqueous solution of GO and CNTs with the use of a surfactant such as sodium dodecylbenzenesulfonate (SDBS) to improve the dispersibility of CNTs, followed by vacuum filtration or a hydrothermal process. Another approach is the use of cationic surfactant polymers such as cetyltrimethylammonium bromide (CTAB) and polyethyleneimine (PEI) to induce electrostatic attraction by introducing a surface charge on CNTs or graphene. However, the use of insulating polymers is not desirable, since it is difficult to completely remove the surfactant polymers, and the amorphous carbon formed after heat treatment of the polymer under an inert atmosphere could deteriorate the electrical conductivity. Furthermore, such composites showed a marginal improvement of electrochemical properties.

Another points, to further explore the macroscopic applications of graphene, an essential prerequisite is the controlled large-scale assembly of twodimensional (2D) graphene building blocks and the transfer of their inherent properties into three-dimensional (3D) structures with a high packing density. Furthermore, graphene needs to be assembled into a microsized powder form considering the powder morphology of activated carbon, which is currently used as an electrode material for EDLCs. Despite the recent progress in realizing graphene assemblies using well-established strategies such as vacuum filtration, layer-by-layer assembly, Langmuir–Blodgett assembly, hydrothermal assembly followed by oven drying, and spray drying, the controllable and scalable assembly of such graphene into graphene microsized powders with a high packing density remains a significant challenge

In this regards, herein, we report the novel integrated Graphene tube @ Graphene Microsphere by using cobalt acetate and dicyandiamide. Graphene tube @Graphene Microspheres (GT@GMs) show a high gravimetric capacitance of 229.8 F g^-1 at 0.1 A g^-1 in 1 M TEABF₄/ACN electrolyte. The GT@GMs exhibited excellent rate capabilities of 94.3 % (gravimetric capacitance at a current density of 2 A g^-1 compared with gravimetric capacitance at a current density of 0.1 A g^-1) with time constants in the range of 0.4 to 0.8 s owing to the favorable formation of pathway by formation of graphene tubes; this allowed the electrolyte to easily penetrate the graphene assembly and facilitated ion transport. Furthermore, all the A-GMs exhibited excellent cycling stability (95.1 % of the initial capacitance retained after 100,000 charge/discharge cycles at a current density of 2 A g^–1) owing to their low oxygen content as well as structural stability originating from the compact assembly of graphene micropores. This study provides new insights regarding the introducing of 1D carbon into graphene to produce graphene-based electrode materials with both high gravimetric capacitances and rate capabilities. Detailed synthetic procedure, electrochemical properties will be discussed at the meeting.

Graphene has been intensively studied for electrode material for electrochemical energy storage devices utilizing its high electrical conductivity and high surface area. Recently introduced electrochemical exfoliation process has many advantages over conventional chemical methods, including low-cost, simple operation, fast production-rate, and in-situ functionalization. In particular, anodic electrochemical exfoliation process is one of the promising methods for fast and simple production of graphene at low cost.

In this presentation, we will first discuss the detailed mechanisms of the electrochemical exfoliation process of graphite into graphene using sulfate containing electrolyte systems. We systematically monitored the structural changes in graphite and associated gas formation during the electrochemical exfoliation process, revealing that water molecules are the main source of gaseous species for the effective exfoliation of graphite into graphene. Next, we will introduce our recent efforts to fabricate 3D structured graphene anodes for Li-, Na-, K-ion batteries. Moreover, we evaluated the temperature-dependent performance of 3D graphene anodes, demonstrating their superior charge storage performance in extreme cold environments.

Environmental benign, inexpensive, flexible, smart energy storage micro-supercapacitors, with high energy and power densities and long-term cyclic stability are appealing for next generation energy storage devices. Conventionally, highly conducting carbon-based nanomaterials with high-surface areas are extensively used as supercapacitor electrode and the introduction of metal oxides (or conducting polymers) induces pseudocapacitance and can further enhances the specific capacitance and energy density. Red mud (RM), an aluminum industry waste by-product which is a rich source of hematite phase Fe₂O_3. RM is environmentally hazardous due to its alkalinity and is produced at an annual rate of ~ 110 million tonnes each year, much of which is not well utilized, and left to lie in large lakes; thus, methods of finding value-added applications for RM are well sought after. In this study, we used mechanical milling to produce uniform spherical RM nanoparticles and utilized these in a flexible micro-supercapacitor device. The as-synthesized nanoparticles were decorated over a laser induced porous 3D graphene (LIG) on a polyimide substrate. The composite electrode material was characterized using transmission electron microscopy (TEM), field effect scanning electron microscopy (FESEM), X-ray photo electron spectroscopy (XPS), Raman spectroscopy and cyclic voltammetry (CV). A solid-state ionic liquid based polymer gel electrolyte was produced using a mixture of ionic liquids {[EMI][TFSI] and [EMIM][BF4]} and a PVDF polymer. Inkjet printing technique was employed to produce the silver current collector and the as fabricated inter-digitated micro-supercapacitor device (Figure 1a) exhibited an areal capacitance of 203 mF cm^-2 with a higher potential window of 2.7 V, high energy density of 0.018 mW h/cm² at 0.66 mW/ cm² power density. RM decoration increased the energy density of the device by 3.7 fold compared with pristine LIG device (Figure 1b). Rapid lateral ion flow in the planar architecture, presence of metal oxides (mostly hematite), higher electrochemically active surface area, better charge transfer kinetics were shown to yield improvements in the energy-density and the electrochemical performance of the device. An in-depth electrochemical study also revealed that the charge storage mechanism was governed by diffusion driven pseudocapacitance. The device exhibited good robustness and could resist bending and flexing and the prototype device exhibited to power a white-light LED (Figure 1c). Overall, this work demonstrates that RM may be used as a low-cost pseudocapacitive element in supercapacitor electrodes and aid in reducing the environmental impact of the aluminium production cycle by recycling this abundant waste product.

Figure 1

A composite of carbon nitride (CN) and reduced graphene oxide¹(RGO) were prepared and used as an electrode material for supercapacitor application. The limited electrical conductivity of carbon nitride is overcome by initially protonating the carbon nitride (p-CN) by refluxing, to increase its conductivity². The p-CN was hydrothermally treated with graphene oxide to form a composite of p-CN/RGO. Morphology was analysed using a scanning electron microscope (SEM); it reveals an interlayered structure of carbon nitride and graphene. The electrochemical behaviour was studied using a three-electrode system using sulphuric acid and potassium hydroxide as an electrolyte. Electrochemical behaviour was studied using cyclic voltammetry within a potential window of -0.4 to 0.75V. The characteristics show a nearly rectangular shape showing the double layer capacitance behavior. The sulphuric acid medium was found to be better electrolyte for the composite as there were no signs of voltage drop in comparison with potassium hydroxide electrolyte. The composite electrode was found to be a better electrode for supercapacitor applications.

References

1 C. Lu, Y. Yang and X. Chen, Nano Lett., 2019, 19, 4103–4111.

2 Q. Li, D. Xu, J. Guo, X. Ou and F. Yan, Carbon N. Y., 2017, 124, 599–610.

Figure 1

There are remarkedly increasing demands in electronic devices including the portable electronic devices and electric vehicles (EVs). Therefore, the energy storages that can store energy efficiently with both high energy and power densities with good cyclability as display in batteries and supercapacitors are needed. The hybrid energy storages are one of the energy storage devices merging the advantages of both batteries and supercapacitors to overcome those lacking properties in each device. Thus, the lithium-ion hybrid capacitors (LICs) are introduced consisting battery-type as negative electrode and supercapacitors-type as positive electrode. There are many selections of electrode materials that can be used in the LICs such as carbonaceous materials and lithium titanate (LTO). The cell configuration was developed and fabricated in organic electrolyte since coin-cell to cylindrical cell. Herein, the 18650 configuration is introduced as hybrid energy storage consisting LTO and activated carbon as negative and positive electrodes, respectively. Moreover, the additional additives in electrolyte are also studied and investigated to improve the electrochemical performances to the hybrid capacitors.

Sodium (Na)-based batteries are considered to be the next-generation cost-effective energy storage devices due to the low cost and high natural abundance of Na sources. Here we present the use of facile-processed nanocarbon to realize two types of high-energy Na-based battery systems: Na-sulfur (S) and Na-carbon dioxide (CO₂) batteries. A highly stable room-temperature (RT) Na-S battery is achieved using a facile-processed nanocarbon promoted S cathode and polymer electrolyte (PE). The RT Na-S battery can deliver a reversible capacity of >700 mAh g⁻¹ with near 100% Coulombic efficiency and an ultrahigh capacity retention of 98.2% at 0.2C after 200 cycles. Moreover, an all-solid-state Na-CO₂ battery is constructed using a nanocarbon-based cathode and a liquid-free PE. The all-solid-state Na-CO₂ batteries exhibit excellent performance with long cycle life (320 h with a fixed capacity of 1,000 mAh g⁻¹), high discharge capacity (>10,000 mAh g⁻¹), and high energy density (180 Wh kg⁻¹ in pouch cell) at 50 ^oC.

The marine energies constitute a strategic sector of the renewable energies to diversify and complete the energy mix. At present, offshore wind energy and the marine turbines are the main approaches. In stages of more upstream research, demonstrators of wave energy converters (WEC) based on a hydraulic conversion have difficulty in developing because of problems of reliability. The harnessing of this field of wave energy could find a new impetus thanks to the development of concepts in break based on innovative and economically technologies: electroactive polymers (EAP). Based on the distortion of an EAP which plays the double role to get the wave energy and to convert it in electrical energy, these generators open interesting perspectives of development because they free themselves from mechanical absorber at the origin of numerous failures of the WEC.

Among challenges identified for the realization of performant EAP-WEC, the availability of more successful materials to convert the mechanical energy is at the heart of the concerns. Starting from carbon nanotubes nano-object to end in a viable mechanical structure, we have developed methods and processes which will be implemented in the future technologies of the wave energy but also aim at the manufacture of a functional prototype of laboratory.

Our strategy is based on the incorporation of nano/micro hybrid reinforcements of carbon nanotubes within a silicone matrix in order to realize (i) flexible conductive electrodes and (ii) to improve the properties of the active material. A parylene coating of carbon nanotubes has demonstrated to reduce percolation and thus an improvement of the dielectric strength of the active silicone matrix. Finally, mechanical – electrical conversion is undoubtedly improved by this approach as confirmed by mechanical tests, dielectric spectroscopy and dielectric strength.

Acknowledgements : The authors thankfully the national French program ANR SEASEA for funding.

The Shockley-Queisser limit places an upper bound on solar conversion efficiency for a single p-n junction solar cell at slightly more than 30%. To surpass this limit, multi-exciton generation is being explored in inorganic semiconductors, while singlet fission (SF) is being investigated in arrays of conjugated organic molecules. In an optimal SF process, the lowest singlet excited state of one molecule (S₁) that is positioned next to a second molecule in its ground state (S₀) is down-converted into two triplet excited states (T₁) each residing on one of the two adjacent molecules. The two triplet states initially form a correlated pair state ¹(T₁T₁), which then evolves into two separated triplet states (T₁ + T₁). As such, the energetic requirement for SF is E(S₁) ≥ 2 ´ E(T₁).

We have set our focus in recent years on intramolecular SF in molecular carbon materials and their studies in solution rather than on intermolecular SF investigations in crystalline films.

Implicit in intramolecular SF is a resonant, direct excitation of the SF material. In dimers of molecular carbon materials linked by a myriad of molecular spacers, SF takes place with quantum yields of up to 200%. In addition, all key intermediates in the SF process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons, have been identified. This approach is, however, limited to the part of the solar spectrum, where, for example, the dimers of carbon materials feature a significant absorption cross-section. To employ the remaining part of the solar spectrum necessitates non-resonant, indirect excitation of the SF materials via either up- or down-conversion. For example, the up-conversion approach is realized with singlet excited states , which are accessed by two-photon absorptions (TPA). TPA is then followed in the second step of the sequence by an intramolecular SF – similar to what is seen upon resonant, direct excitation. Quite different is the down-conversion approach, which is based on an intramolecular Förster resonance energy transfer (FRET) and thereby the (photo)activation of the SF material. FRET requires the use of a complementary absorbing chromophore and enables funneling its excited state energy unidirectionally to the SF performing pentacene dimer. Again, SF completes the reaction sequence.

The conversion of waste heat into electricity using solid state devices, namely thermoelectrics, based on carbon materials has experienced renewed interest in the last decade as these materials are particularly suited for large area and low-temperature operation applications since they are abundant, low-toxicity and easy to process [1].

In this presentation we will focus on our recent attempts to further extend the sustainability and range of applications of CNT based thermoelectrics. First, we will describe the use bacteria in environmentally friendly aqueous media to grow large area bacterial nanocellulose (BC) films with an embedded highly dispersed CNT network [2]. The thick films are fully bendable, can conformally wrap around heat sources and are stable above 500 K. The resulting composite films exhibit comparable thermoelectric properties to buckypapers while saving more than 90% of the carbon nanotubes. Interestingly, BC can be enzymatically decomposed, thus completely reclaiming the embedded CNTs once the generator has reached the end of its lifetime. Second, we will show our recent studies on the stability of CNT based thermoelectrics, aimed at precisely extending their operational lifetime.

Finally, we employ the low thermal conductivities of these composites, granted by the phonon stack-electron tunnel behavior [1], to demonstrate their use as solar thermoelectrics, i.e. materials that convert the energy of the absorbed sun light into heat, and then into electricity [3].

[1] Will organic thermoelectrics get hot? M. Campoy-Quiles, Philosophical Transactions of the Royal Society A, 377, 20180352 (2019).

[2] Farming thermoelectric paper, D. Abol-Fotouh, B. Dörling, O. Zapata-Arteaga, X. Rodríguez-Martínez, A. Gómez, J. S. Reparaz, A. Laromaine, A. Roig and M. Campoy-Quiles, Energy and Enviromental Science, 12, 716-726 (2019).

[3] Solar harvesting: a unique opportunity for organic thermoelectrics? José P. Jurado, B. Dörling, O. Zapata‐Arteaga, A. Roig, A. Mihi and M. Campoy‐Quiles, Advanced Energy Materials, 1902385 (2019). DOI: 10.1002/aenm.20190238

Single-walled carbon nanotubes (SWCNTs) exhibit many unique properties arising from their quantum confinement. However, the lack of a controllable large-scale alignment procedure had limited the exploration of their unique properties. Our recent work has overcome this problem by demonstrating a vacuum-filtration based technique to align SWCNTs on wafer-scale. These aligned SWCNT films exhibit many interesting optical properties such as extreme optical anisotropy or hyperbolic dispersion. Besides, aligned SWCNTs are flexible, refractory (stable up to 1900 K), inexpensive, and based on earth-abundant carbon making them an excellent refractory infrared nanophotonic material platform. Such a refractory infrared material platform is exactly what is necessary to enable efficient thermophotovoltaic energy conversion.

Thermophotovoltaics is a solid-state heat-to-electricity conversion technique. It relies upon photovoltaic conversion of thermal light emanating from a hot surface to electricity. The broadband nature of thermal light makes the thermophotovoltaic conversion inefficient. Optical resonators, filters, spectrally selective thermal emitters are a few methods proposed to increase the efficiency of thermophotovoltaics. Selective thermal emitters are very promising due to their ease of design and integration. Selective thermal emitters are hot surfaces that emit thermal radiation in a narrow spectral band above the bandgap of the photovoltaic cell. The suppression of thermal emission below the bandgap and enhancement above the bandgap are the key requirements for efficient thermophotovoltaic conversion. Generally, optical properties of materials at high temperatures limit the performance of such selective emitters and the current efficiency record is about 8%. But, the hyperbolic optical property of aligned SWCNTs together with their thermal stability make aligned SWCNTs ideal for efficient thermophotovoltaics.

Here in this work, we study the infrared optical properties of aligned SWCNTs at high temperatures (1000 K) and demonstrate spectrally selective thermal emission from plain and nano-patterned thin films. Using deep sub-wavelength sized optical cavities, we show that aligned SWCNTs exhibit hyperbolic dispersion in almost of all of infrared and enhance thermal photon density by at least 100 times. Such a large enhancement in thermal photon density leads to a large suppression of unwanted sub-bandgap thermal photons and a large enhancement of above-bandgap photons. Our analysis shows that aligned SWCNTs enable 30% or higher thermophotovoltaic efficiency when operating at 1300 K with no concentration. With near-field concentration, aligned SWCNTs can allow conversion efficiencies over 50%.

Electronic ratchets are recently demonstrated thin-film semiconductor devices with the ability to harvest energy from high-frequency signals or electrical noise. The state-of-the-art electronic ratchets have been fabricated from doped conjugated polymers, but the device performance is limited by the low charge-carrier mobility and relatively poor electrical conductivity. Enriched semiconducting single-walled carbon nanotube (s-SWCNT) networks represent an attractive alternative to conjugated polymers, since they are easy to dope and exhibit good charge-carrier transport.

While the electronic ratchet device is based on a simple field-effect transistor architecture, it requires the generation of asymmetry within the transistor channel. In this presentation, we will outline the approaches employed to control the charge-carrier doping profile to create this asymmetry. We will subsequently discuss the performance of these carbon nanotube electronic ratchets and make a comparison with their conjugated polymer counterparts.

The enormous strides researchers have made in advancing perovskite-based photovoltaics in the past few years are fueling the dream of a rapid entry of this highly promising technology into the global energy market. This seems like serendipitous timing since solar power has gained an enormous momentum over the past decade exceeding all projections. This expansion in solar power is driven by an increasing understanding that climate change requires immediate action, in particular with regards to power generation; and simultaneously, the price for photovoltaic modules has remarkably quickly fallen to make solar power generation competitive vis-à-vis conventional technologies.

Compositional tuning of the perovskite absorber has led to immense improvements in stability and efficiency of perovskite solar cells leading to a certified efficiency of over 25% for a single-junction laboratory device. The successful transition of a photovoltaic technology from the lab into the field requires, however, two additional important parameters aside from efficiency which are essential for real-world deployment: stability and scalability.

We propose using single-walled carbon nanotubes (SWCNTs) as an alternative p-type layer for future application in perovskite solar cells.

Carbon nanotubes combine several highly attractive characteristics such as chemical inertness and mechanical resilience with intrinsically high charge-carrier mobilities endowing them with a unique potential for a much more stable dopant-free charge-selective contact. Furthermore, the SWCNT deposition techniques for large-scale use, such as spray coating, are already well-established opening clear avenues for direct implementation in a real-world industrial setting.

We demonstrate that a cascade-like transfer extraction through SWCNTs can minimize photovoltage losses by suppressing non-radiative recombination. By further improving the absorber quality, the voltage losses in solar cells can be reduced to around 340 mV which is comparable to conventional III-V semiconductor-based photovoltaics.

By further enhancing the selective charge extraction at the perovskite-SWCNT interface through interfacial charge transfer doping, we achieve steady-state efficiencies approaching 22% for alloyed narrow bandgap perovskites, illustrating the versatility and excellent performance of SWCNTs as contact material.

Single-walled carbon nanotubes (SWCNT), graphene, and fullerene (C₆₀ and PCBM) are very efficiently used in organic-inorganic Perovskite solar cells [1,2]. A film of carbon nanotubes or graphene can be the practical replacement of ITO for the flexible transparent electrode of inverted perovskite solar cells [3]. Doping of SWCNT is essential for high performance solar cells through increased in-plane film conductivity and energy level adjustment. Since p-doping is easier than n-doping, it is more practical to use SWCNT electrode in the hole-transport side. Hence, we have developed the normal type perovskite solar cells composed of ITO/ETL/MAPbI₃/(HTL)/SWCNTs. The use of SWCNT as the top electrode instead of metal electrode is also enhances the stability of PSCs by removing the metal-ion migration, and considerably reduces the fabrication cost, and suitable for the development of tandem system. The normal-type perovskite solar cell, composed of ITO/C₆₀/MAPbI₃/SWCNTs, can achieve a PCE of 17 % with spiro-MeOTAD as dopant (or HTL) to SWCNTs [4]. The better performance of solar cells can be obtained by tuning of energy level of SWCNT with Trifluoromethanesulfonic acid (TFMS) doping. For 2D/3D FACsPbI₃ system we have reached PCE of 17.6% [5]. Recently, we have developed further by using high concentration of hole-transporting material [6]. For MAPbI₃ system, we have obtained the highest PCE of 18.8%. This PCE is higher than that of the metal electrode-based control devices, which gave a PCE of 18.1%.

Finally, the ultimately inorganic stable doping of SWCNT could be possible by using the one-dimensional van der Waals hetero-nanotubes [7]. We have synthesized the coaxial few-layer hexagonal boron nitride nanotube (BNNT) around a single-walled carbon nanotube (SWCNT); SWCNT@BNNT. Then, the further coating of coaxial MoS₂ nanotubes results SWCNT@BNNT@MoS₂NT. The inner SWCNT and outer MoS₂NT are electrically coupled through a few layer BNNT. This new structure shown in Fig. 1 is expected to give extra functionality, durability in the solar cell devices.

Part of this work was supported by JSPS KAKENHI Grant Numbers JP15H05760, JP18H05329.

References:

[1] I. Jeon, Y. Matsuo, S. Maruyama, Topics Curr. Chem., 376:4, (2018)1.

[2] I. Jeon, R. Xiang, A. Shawky, Y. Matsuo, S. Maruyama, Adv. Energy Mater., (2019)1801312.

[3] I. Jeon, J. Yoon, N. Ahn, M. Atwa, C. Delacou, A. Anisimov, E. Kauppinen, M. Choi, S. Maruyama, Y. Matsuo, J. Phys. Chem. Lett., 8 (2017) 5395.

[4] N. Ahn, I. Jeon, J. Yoon, E. I. Kauppinen, Y. Matsuo, S. Maruyama, M. Choi, J. Mater. Chem. A 6 (2018) 1382.

[4] I. Jeon, S. Seo, Y. Sato, C. Delacou, A. Anisimov, K. Suenaga, E. I. Kauppinen, S. Maruyama, Y. Matsuo, J. Phys. Chem. C, 121 (2017) 25743.

[5] J.-W. Lee, I. Jeon, H. Lin, S. Seo, T.-H. Han, A. Anisimov, E. I. Kauppinen, Y. Matsuo, S. Maruyama, Y. Yang, Nano Lett., 19 (2019) 2223.

[6] I. Jeon, A. Shawky, A. Anisimov, E. I. Kauppinen, Y. Matsuo, S. Maruyama, submitted (2019).

[7] R. Xiang, T. Inoue, Y. Zheng, A. Kumamoto, Y. Qian, Y. Sato, M. Liu, D. Gokhale, J. Guo, K. Hisama, S. Yotsumoto, T. Ogamoto, H. Arai, Y. Kobayashi, H. Zhang, B. Hou, A. Anisimov, Y. Miyata, S. Okada, S. Chiashi, Y. Li, E. I. Kauppinen, Y. Ikuhara, K. Suenaga, S. Maruyama, arXiv:1807.06154 (2019).

Figure 1

Energy conversion and storage via direct electrochemical oxidation and reduction processes, such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), can provide a clean, efficient, and economically viable means of meeting this sustainability challenge, by allowing stored renewable energy to be reliably delivered where and when it is needed. During the development of the highly demanded nonprecious metal catalysts to replace precious metals for these applications, carbon catalysts have many advantages over metal oxides, including excellent electrical conductivity, high surface area, and easy functionalization. However, most carbon-based catalysts suffer from poor activity and stability for the more challenging OER under a highly oxidative conditions. This represents one of grand challenges in energy conversion research societies.

For the first time, this work demonstrated that a new class of large-diameter tubular nanocarbon (>500 nm in diameter) catalyst is capable of catalyzing both the ORR and the OER with activity comparable to Pt and exceeding Ir, respectively, for these two reactions. Most importantly, the tube catalyst exhibited good stability upon cycling across a wide potential window (0 to 1.9 V vs RHE) in 0.1 M NaOH electrolyte. The high OER activity was verified using well-designed electrochemical tests, demonstrating that the current generated during the OER arose solely from oxygen evolution, rather than carbon oxidation. This is the first example of such excellent OER activity and durability of a nanostructured carbon-based electrocatalyst across the complete ORR-OER potential window. The newly developed carbon tubes were synthesized via a one-step template-free graphitization process using inexpensive dicyandiamide (DCDA) precursor as carbon/nitrogen source and a ternary FeCoNi alloy as a catalyst. Generation of a mixed metal catalyst, i.e., FeCoNi during the graphitization process is the key factor to yield the largest tube size for maximum electrochemically accessible surface areas, dominant graphitic nitrogen doping, and thicker tube walls, which are associated with the significantly improved activity and durability. The cost effective, easily scalable, single step and environmentally benign synthesis procedure further favors this nanocarbon's application as a practical bifunctional electrocatalyst for the ORR and OER, with potential to advance the development and commercialization of regenerative fuel cell systems and rechargeable metal-air batteries. The use of nanostructured carbon as bifunctional ORR/OER catalysts will open up new research direction in this field and further advance the role of carbon nanomaterials in oxygen electrocatalysis for energy conversion and storage.

High cost of the platinum-based catalysts for the sluggish oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) is delaying wide-spread commercialization of fuel cell electric vehicles (FCEVs). It is crucial to develop highly-active and cost-effective materials to reduce amount of platinum usage and eventually to replace the platinum-based catalysts. In this respect, nitrogen-doped carbon incorporated with atomically-dispersed metal and/or metal nanoclusters (M-N-C) has attracted tremendous attention owing to their high catalytic activity towards ORR. By atomically dispersing Pt or forming Pt nanoclusters in the nitrogen-doped carbon, utilization of Pt can be maximized, resulting in ultralow usage of Pt catalyst. Fe incorporated in the nitrogen-doped carbon (Fe-N-C) has been reported as the best candidate to attain high ORR activity among the non-precious catalysts. In applying these catalysts for PEMFC, it is still required to improve activity and durability of those M-N-C catalysts in the harsh acidic environment of PEMFC.

Herein, we present Pt-N-C and Fe-N-C as highly-active ORR catalysts prepared through a facile method. To enhance ORR activity of those M-N-C catalysts, a hetero-atom is doped into the M-N-C catalyst. In addition, effects of formation of metal nanoclusters on the ORR activity are investigated with respect to the size of the nanoclusters. DFT calculation study explores active sites for the ORR in M-N-C catalysts by examining the oxygen adsorption energy of reaction intermediates towards benefiting ORR.

Nowadays, the increasing concentration of CO₂ emission in our atmosphere is a serious environmental issue. According to an issue for preserving Earth's Climate in the 13^th UN Sustainable Development Goal, technologies that reduce both the carbon emissions of existing processes and those that efficiently utilize CO₂ as feedstock for chemicals and fuels are necessarily required. Electrochemical reduction of CO₂ (CO2R) is a promising method for converting this greenhouse gas into value-added products, utilizing renewable energy. A limitation is that CO₂ is inert molecule () that requires considerable energy for chemical activation. In addition, the CO2R includes multiple steps of electron and proton transfer on catalyst surface. In general, the reduction potentials and product distribution for CO2R depend on experimental conditions, electrolytic solutions, and electrode materials. Herein, we used CVD nitrogen‐doped graphene on copper foam as carbo-/electro-catalyst (N-GP/Cu). To understand the selectivity of the as-prepared catalyst, we observe the electrochemical reduction product from CO2R using a combination of cyclic voltammetry (cv) and on-line mass spectrometry (DEMS). The presence of nitrogen heteroatom on the graphene sheet reduces the onset potential at ca. 0.5 V (vs. SCE) in 0.1M KHCO₃ under CO₂ gas. The N-GP/Cu can mainly convert CO₂ into CO. We hope that this study may provide a guideline to develop the improved CO₂ conversion catalyst.

Oxygen-atom functionalization of chemical intermediates is critical for the production of diverse textiles, plastics, and pharmaceuticals, including epoxides and ketones. The wet chemical and thermochemical routes used today suffer from large carbon dioxide footprints, stoichiometric waste products, and hazardous reagents. We have developed a route whereby water can be used as the oxygen atom source in functionalization reactions of hydrocarbons. At the cathode, hydrogen is selectively generated. Overall, this reaction provides a means by which the oxidizing equivalents can go towards generating a valuable product rather than generating oxygen which is simply vented in a conventional water electrolyzer. We have developed mechanistic understanding of how water is oxidized, providing means by which the selectivity for oxygen-atom functionalization can be rationally improved.

With impending serious concerns associated with climate change and the depletion of fossil fuels, an envisaged hydrogen economy remains a viable alternative for addressing future energy issues. However, the significant technical challenges from vehicular hydrogen storage systems such as weight, efficiency, safety and cost constraints must be properly resolved before a commercial application is possible. Compared to compressed high-pressure and liquid hydrogen storage systems, storing hydrogen in solid systems via chemisorption and physisorption is emerging as a promising approach for hydrogen storage [1-3]. In this presentation, recent advances in the solid-state hydrogen storage with a high volumetric density are highlighted.

In addition, graphene-based nanomaterials have been considered as a promising candidate for hydrogen storage due to its lightweight and high surface area [4]. We have synthesized graphene oxide (GO), reduced graphene oxide (rGO) and boron-doped reduced graphene oxide (B-rGO) and investigated their performance for hydrogen storage. To enhance their capacity for hydrogen storage, the fabricated graphene oxide based nanomaterials were further modified with palladium (Pd) nanoparticles. The morphological features, structure and chemical compositions of the synthesized nanomaterials (GO, rGO and B-rGO) and nanocomposites (Pd/GO, Pd/rGO and Pd/B-rGO) were characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy, showing that Pd nanoparticles were uniformly dispersed on the B-rGO surface. Cyclic voltammetry and galvanostatic charging-discharging technique were employed to probe the hydrogen storage capacity of the graphene based nanomaterials and the nanocomposites. The effect of the boron substitution and the Pd nanoparticle decoration on the hydrogen storage are discussed.

References:

[1] A. Chen, C. Ostrom. Palladium-based nanomaterials: synthesis and electrochemical applications. Chem. Rev. 115 (2015) 11999 - 12044.

[2] S. Konda, A. Chen, Palladium based nanomaterials for enhanced hydrogen spillover and storage. Mater. Today 19 (2016) 100 - 108.

[3] E. Boateng, A. Chen, Recent advances in nanomaterials-based solid-state hydrogen storage. Mater. Today Adv. (2019) in press.

[4] S. K. Konda, A. Chen, One-step synthesis of Pd and reduced graphene oxide nanocomposites for enhanced hydrogen sorption and storage. Electrochem. Commun. 60 (2015) 148–152.

Nanostructured carbon and carbon composite materials have been key component in almost all electrochemical energy devices, such as fuel cells, batteries, supercapacitors. In this talk, we will present our work on nanostructured carbon composite materials for electrocatalysis, including oxygen reduction reaction (ORR), electrocatalytic hydrogenation, with a focus on materials stability. We will introduce fundamental understanding on the degradation mechanisms of this kind of carbon-based materials, including electrochemical and chemical oxidation (by radicals) – for atomically dispersed M-N-C nonprecious metal catalysts, it also includes the stability of metals. Our strategy to improve the stability of carbon-based materials will also be presented, including incorporation of metal oxides to protect carbon defects and to scavenger radicals.

Due to the influence of human beings in the modern society, the concentration of CO2 in the atmosphere is rapidly increasing, which causes various environmental problems such as abnormal climate caused by global warming and destruction of ecosystem due to ocean acidification. Therefore, many institutional, scientific, and engineering efforts are being made to reduce the concentration of CO2 in the atmosphere. From the scientific point of view, to make the fuels and chemicals we need from the atmospheric CO2, electrochemical reduction of CO₂ is actively being studied. The electrochemical CO₂ reduction reaction can be divided into two categories, one for synthesizing multi-carbon products directly such as ethylene or ethanol and the other for producing syngas mixed with CO and H₂. The former is mainly researched on Cu based material and has an advantage in that the desired product can be obtained immediately. In the latter case, by adjusting the ratio of CO and H₂ in the synthesis gas, it is possible to synthesize multi-carbon products. The latter method can be said to have an advantage in the purity of the gas phase produced (reduction of separation cost). Research is underway in the form of co-catalysts of CO production catalyst like Au, Ag, Zn, Cu & H2 production catalysts. Because simply increasing the current density is not a good thing, but it must be able to maintain an industrially meaningful range of syngas ratios (1 to 3) while producing a high current density. Therefore, the potential window of studies on the rate-controlled syngas studied so far is typically high below -1.2V Vs RHE and high current density of ~ 30 mA/cm². The reported lifetime at this level of current density is less than 10 hours, and for papers that report longer lifespans of tens to 100 hours, measured at 1 to 2 mA/cm² levels. We fabricated Ag nanoparticle embedded in Zn dispersed carbon nanofiber to maintain syngas ratio stably in high potential window. In this catalyst carbon nanofiber produces H₂ and Ag produces CO and dispersed Zn helps Ag in high potential.

We annealed electrospun PAN/zinc nitrate&silver nitrate nanofiber at 800°C 3h in N₂ ambient after stabilization in air. From this, we obtained Ag nanoparticle embedded in Zn & N doped carbon nanofiber. Ag tends to form nanoparticle and non-particle Zn was dispersed in carbon nanofiber. we obtained almost potential insensitive syngas ratio unlike conventional Ag catalyst in syngas production. Only N-doped carbon nanofiber sample produced increasing H₂ with potential. Zn & N doped carbon nanofiber produced ratio of syngas higher than 2. Ag nanoparticle embedded carbon nanofiber produced ratio of syngas lower than 1 and sharply increased in higher potential (< -1.6V Vs. RHE). However, Ag nanoparticle embedded in Zn & N-doped carbon nanofiber maintained its low ratio of around 0.5 even in -2.2 V Vs. RHE and almost potential insensitive. We altered this insensitive syngas ratio with the mass ratio between carbon nanofiber and Ag/Zn-carbon nanofiber. It made syngas ratio increases slowly with potential and overall syngas ratio can be shifted with the mass of carbon nanofiber.

A synergistic, nanoscale electrical-interface with the membranes of exoelectrogenic microbes will have transformative impact on biological cell based electronic-devices. In this presentation, we will report a conformal graphenic interface on biocatalytic Geobacter sulfurreducens membrane that results in quantum-capacitance induced n-doping in graphene. This further enhances electron shuttling from the membrane to improve electron harvesting from the electrogenic membrane. The quantum coupling of reduced graphene oxide (rGO) with the connected protein-membrane channels leads to an additional electron density of 3.44 x 10¹² cm^-2 and an increase in the in-plane phonon vibration energies (G) of rGO by 5 cm^-1. This n-doping enhances the electron transfer-rate from the cell membrane into the rGO improving the power density of a simplistic microbial fuel cell (MFC) by ~ 2 folds. The synergistic electron-harvesting and conformal membrane-interfacing of flexible 2D nanomaterials can lead to an evolution in the design of microbe-circuitry to power stand-alone nanodevices.

Figure 1

Current energy demands and technological advancements will require a wide array of energy storage devices such as supercapcitors that can deliver large quantities of energy quickly. Electrochemical double layer capacitors (EDLC) are capable of cycling thousands of times with minimal drop in total capacitance, and when used with an ionic liquid electrolyte they can deliver higher energy densities due to high operating voltages. Surface area, and pore size distribution play a critical role in the performance of EDLC devices due to their relationship to capacitance. Therefore, electrospun carbon nanofibers are a promising EDLC electrode material due to their high surface area, conductivity, and cyclability. Their surface area can be tailored with the inclusion of in-situ porogens in the polymer precursor and activation during carbonization. Polymer derived carbon fibers have been produced from polyacrylonitrile (PAN) using immiscible blends with sacrificial polymers like polystyrene (PS). The resulting carbons have high surface areas (>2,000 m²g^-1), but a wide distribution of pore sizes. Altering the miscibility of the sacrificial polymer with the copolymer poly(styrene-co-acrylonitrile) (SAN) affords a unique fiber morphology with a high microporosity.

Figure 1

Multi-redox organic and organometallic electrode materials have been emerging alternatives to the widespread inorganic counterparts in advanced power sources due to their design diversity, light weight, flexibility, and environmental benignity.¹ However, their electrically insulating nature, limited capacity, and poor durability should be resolved for the practical application.

Here, we present a one-dimensional (1D) nanohybrid composed of a multiwalled carbon nanotube (MWCNT) core and a cobalt porphyrin shell (Figure) as a new class of electrode materials for rechargeable lithium batteries.² Highly π-conjugated and multielectron redox-active meso-tetrakis(4-carboxyphenyl) porphyrinato cobalt (CoTCPP) shows strong noncovalent interactions with the MWCNT, leading to the successful formation of the 1D nanohybrid. The resultant nanohybrid, due to its structural uniqueness and maximal use of active areas, facilitates electron transport and electrolyte accessibility, which thus contribute to exhibiting a high specific capacity and improving redox kinetics. Furthermore, intrigued by the 1D structure of the nanohybrid, an all-fibrous nanomat electrode was fabricated through concurrent electro-spraying/-spinning processes. The nanomat electrode provides bicontinuous electron and ion conduction pathways, which eventually reveals the well-distinguishable lithiation behavior of CoTCPP and exceptional electrochemical performances with a long-term stability (ca. 226 mAh g^‒1based on the electrode sheet weight at a current density of 5 C for over 1500 electrochemical cycles).

We hope that the material design strategy described in this study offers new insight into the development of high-performance electrode materials for next-generation power sources and energy storage systems.

References:

1. T. B. Schon, B. T. McAllister, P. F. Li, D. S. Seferos, Chem. Soc. Rev.2016, 45, 6345.

2. K. Jeong, J.-M. Kim, S. H. Kim, G. Y. Jung, J. Yoo, S.-H. Kim, S. K. Kwak, and S.-Y. Lee, Adv. Funct. Mater.2019, 29, 1806937.

Figure 1

Carbon nanoparticles (CNPs) are considered as one of the most promising materials due to their unique optical and electronic properties for a wide range of applications in the field of optoelectronics, energy conversion/ storage and bio-imaging. The high photoluminescence, photostability and low toxicity of CNPs have made them suitable for various applications. The unique network of hybridized sp² carbon atoms provides unique properties of CNPs as it allows delocalization of the electrons over the entire surface of the molecule. The studies have shown that the carbon core is responsible for the strong absorption of light while the luminescence comes from the surface sites and the functional groups present on the surface. The functions and properties of the CNPs could be modulated by changing their shape, size and dimensionality. Despite all these advantages, CNPs have been slow to transform from laboratory prototypes into real life industrial scale products because of the difficulty in synthesizing them and in controlling their size. The control over their size is important as the optical properties of CNPs have been shown to be varying with the variation in size. The synthetic methods reported until now involves high-temperature (>100 ^oC) processes which often results in uncontrolled shape, size, polydisperse and chemically inert nanoparticles, which makes it very difficult to modulate their optical, electronic and morphological properties. Thus, the development of low-temperature, controlled synthesis is desirable.

We report the development of new synthetic methods for the preparation of carbon nanoparticles allowing precise control of their shape, size and properties by polymerization of sp-carbon rich precursors. These precursors (butadiyne and acetylene) tend to become thermodynamically unstable when polymerized to long polyyne chains and decompose inside the reaction mixture to give CNPs. Hence, these polyyne intermediates provide us the control over the size of CNPs during the reaction and in turn, over their properties for further modulation and functionalization. The size-tunable nanoparticles were synthesized in a single step from different polymerization techniques such as dispersion and micro-emulsion with Glaser-Hay polymerization. The size of the resulting carbon nanoparticle is controlled by changing different reaction parameters such as the monomer loadings and the concentration. The control over the different parameters allows us to obtain monodisperse spherical CNPs with a size in the range of 25 nm to 250 nm and use of low temperature methods (<100 ^oC) allows us to overcome the limitations associated with current methods. After isolation, CNPs were characterized by dynamic light scattering, microscopy to analyze the shape and size of the CNPs. To analyze the nature of carbon molecules, Raman spectroscopy and FTIR were used. The optoelectronic behavior of the CNPs was characterized in order to establish the size-property relationships.

Proton exchange membrane fuel cells (PEMFC), which are promising eco-friendly energy sources, need to operate under low humidity conditions in order to be applied for small electrical devices. In such low relative humidity condition, hydration of membrane electrode assembly in the fuel cell system is an important key to prevent performance degradation due to decreased ion conductivity of the Nafion® membrane. Herein, amorphous carbon capsuled carbon nano-onions (AC-CNO) were prepared by irradiating a laser to gaseous hydrocarbons flame capable of mass continuous production. The particles have high-quality graphitic layers in the form of spherical multi-shelled fullerenes and the outermost layer is surrounded by oxygen functionalized amorphous carbon. The particles of various sizes with the same morphology can be produced, and the hydrophilicity of particles with different sizes varies due to the structural characteristics in the catalyst layer and the amount of -OH functional groups attached to the amorphous carbon. The Pt/AC-CNO-3 catalyst layer made of AC-CNO with an average size of ~170nm was deposited on the anode electrode and the membrane electrode assembly (MEA) shows the best performance under low humidity, compared to MEAs with commercial Pt/C deposition; the current density reached 1200mA/cm² at 0.6V and maximum power density reached 1080mW/cm² with operating at 50% RH, 80℃ cell temperature under 1.8bar back pressure, while 870mW/cm² in case of commercial catalyst Pt/C.

Electrochemical reduction reaction of CO₂ (CO₂ RR) to valuable products offers potential for storing excessed renewable energy as well as chance to close the carbon loop, displacing the fossil fuel in chemical industries. Major efforts have been made to direct conversion of CO₂ to ethylene which is widely used building blocks for chemical industries with large market size. Recently, tandem electrocatalysts composed of Cu and promoter metals which produces CO such as Au, Ag, and Zn have been investigated to enhance ethylene selectivity by increasing local concentration of CO*, overcoming limitation of pure Cu. However, these catalysts fabricated by sequential deposition of promoter metals on copper have limits in difficulty of controlling proximity between activated CO production sites and copper surfaces.

Carbon is known for good supporter for the electrocatalyst due to the good electrical conductivity and electrochemical stability. In addition, Doped nitrogen in the pyridinic or pyrrolic configurations acts as the active site of CO2 reduction to CO. However, many researches have been reported carbon as supporter or catalyst producing CO gas, not as CO supplying co-catalyst with Cu. This may be caused by difficulty of composing nitrogen uniformly in carbon and in the proximity of Cu. Here, we have developed a new organic-metal hybrid tandem catalyst composed of Cu particles embedded in N-doped carbon nanofiber (Cu/N-CNF) and N atoms located on the periphery of Cu particles via "one-pot selective oxidation".

In order to fabricate Cu/N-CNF, electrospun copper acetate (CuAc: Cu(CO₂CH₃)₂)/polyacrylonitrile (PAN: (C₃H₃N)_n) nanofibers were calcinated at thermodynamically designed oxygen-controlled conditions based on Ellingham diagram. Cu-embedded undoped carbon nanofiber (Cu/CNF) catalysts were also synthesized by same process as Cu/N-CNF using polyvinyl alcohol (PVA : (C₂H₄O)_n) instead of PAN. During calcination, temperature was maintained at 800 ºC for 5 h under 50 mTorr of pO₂ at which the carbon is combusted and the copper is reduced, besides, the nitrogen hardly reacted with oxygen during calcination. It was confirmed that metallic Cu particles are successfully formed in all catalysts by SEM and TEM analysis. Also, Cu/N-CNFs contains pyridinic N predominantly than other N species by SEM and XPS analysis.

The activity and faradaic efficiency (FE) of each product were examined by flow cell reactor with 5 M KOH electrolyte. Cu/N-CNFs show higher current densities compared to Cu/CNF catalyst at measured potential range (-0.2 ~ -0.8 V vs. RHE). Furthermore, Cu/N-CNF shows maximum C₂H₄ selectivity (62%) at much lower overpotential of -0.57 V vs. RHE compared to undoped Cu/CNF (-0.75 V vs. RHE). It can be inferred that increased CO production by doped N promotes CO* dimerization, whereas, without doped N, lower CO* generation limits the maximum amount of CO* dimerization. Furthermore, decrease of the CO dimerization energy barrier by CO production of doped N around Cu particles also will be discussed by DFT calculations.

The rising level of CO₂ in the atmosphere poses a major threat to our global climate [1]. Renewable energy are promising alternatives but the utilization of renewable energy is challenging because of its intermittency. The key solution is to develop an energy storage system that can store energy and then release it as needed. CO₂ reduction reaction (CO₂RR) uses abundant CO₂ present in the atmosphere and renewable energy as the input power. Therefore, increasing interest has been focused on electrochemical routes to transform CO₂ into useful products. However, the reduction of CO₂ is thermodynamically and kinetically unfavorable. To overcome the energy barrier of CO₂RR, the development of high efficiency and high selectivity catalysts is a key goal of CO₂RR research.

Metallic catalysts have attracted much attention for CO₂RR and have achieved some successes. However, most metallic catalysts exhibit large CO₂RR overpotentials and insufficient selectivity. Also, the high price of noble metals is a key obstacle to scale-up and commercialization of these materials for CO₂RR.

Carbon is a very promising candidate to advance CO₂RR due to its high specific surface areas and good conductivity. However, carbon atoms are electrically neutral and therefore it is difficult to activate the CO₂ molecules and adsorb the intermediate. Therefore, it is necessary to develop novel carbon catalysts to enhance their catalytic activity for CO₂RR. Nitrogen is the most commonly used carbon doping atom due to its high electronegativity, which leads to polarization of the adjacent carbon atoms, thus enhancing the electronic/ionic conductivity [2]. Many carbon materials, such as carbon nanotubes and graphene, have been doped with N and investigated as CO₂RR catalysts [3][4], with some N-doped materials exhibiting a 85% Faradaic efficiency towards CO production[5].

In this work, a nitrogen-doped templated nanoporous carbon scaffold (N-doped NCS) was investigated as a catalyst material for electrochemical CO₂ reduction. The NCS is a novel, templated, binder-free, self-supported, fully tunable mesoporous carbon material[6] that gives a high active site density and good conductivity.

NCS material, having a pore size of either 12, 50 or 85 nm, was heated in NH₃ gas at 700 °C for 7 hours to prepare N-doped NCS. SEM and TEM were used to confirm the NCS morphology, while XPS, EDX and elemental analysis were used to determine the N content of the NCS material. The electrochemical performance of the N-doped NCS was carried out first using CV in CO₂ sat. 0.1 M KHCO₃ in a glass cell. After that, a membrane electrode assembly (MEA) CO₂ electrolyzer was used to determine the CO₂ reduction activity. An N-doped NCS (IrO₂-coated) was used as the anode and an anion exchange membrane (AEM) was used as the separator during CO₂ electrolysis, with humidified CO₂ gas used at the cathode side. The gas products were collected from the cathode outlet and injected into a gas chromatography system for analysis. No liquid products were observed in the solution that was released to the cell outlet.

The performance of N-doped NCS will be presented based on the results obtained in various solution-flow cell configurations. Effect of N-doped NCS preparation optimization will also be discussed. Based on both the CV results and the MEA CO₂ electrolyzer data, the onset potential of CO₂RR was comparable to what has been reported by others for N-doped carbons, but the high internal surface area of the NCS, combined with its high extent of N doping, may give the N-doped NCS some advantages. A maximum 90% FE_CO was achieved and the stability of the catalytic material was also studied in the flow cell systems.

References

[1] C. Costentin, M. Robert, and J.-M. Savéant, "Catalysis of the electrochemical reduction of carbon dioxide," Chem. Soc. Rev., 2013.

[2] T. Zheng, K. Jiang, and H. Wang, "Recent Advances in Electrochemical CO₂ -to-CO Conversion on Heterogeneous Catalysts," Adv. Mater., vol. 30, no. 48, p. 1802066, Nov. 2018.

[3] X. Wang et al., "Emerging Nanostructured Carbon-based Non-precious Metal Electrocatalysts for Selectively Electrochemical CO₂ Reduction to CO," J. Mater. Chem. A, 2019.

[4] H. Cui, Y. Guo, L. Guo, L. Wang, Z. Zhou, and Z. Peng, "Heteroatom-doped carbon materials and their composites as electrocatalysts for CO₂ reduction," J. Mater. Chem. A, vol. 6, no. 39, pp. 18782–18793, 2018.

[5] T. Ma et al., "Heterogeneous electrochemical CO₂ reduction using nonmetallic carbon-based catalysts: current status and future challenges," Nanotechnology, vol. 28, no. 47, p. 472001, Nov. 2017.

[6] Birss, Viola, L. I. Xiaoan, and Dustin Banham. "Porous carbon films." U.S. Patent Application No. 15/124,847.

Finding cost effective catalysts for the oxygen reduction reaction (ORR) is one of the most overriding challenges in the field of electrochemistry [1]. Carbon-based materials emerge as one of the promising candidates due to their remarkable advantages of low cost, abundant structural variety, tailorable surface chemistry, and good conductivity. Tremendous efforts have been made to improve the performance of carbon-based materials for the ORR, mainly through modifying the inherent structures of carbon by doping heteroatoms (e.g., B, N, P) or combining with metal/metal oxides. We have demonstrated recently that modifying Pt-based catalysts by a minor amount of ionic liquid (IL, e.g., [BMIM][NTf₂], [MTBD][NTf₂]) could significantly boost their ORR activity [2-5]. This innovative strategy has also been successfully transferred to some non-precious metal Fe-N-C catalysts, on which an ionic liquid ([BMMIM][NTf₂]) modification is found to boost both their activity and stability [6]. In the current contribution, we will present our latest progress toward boosting the emerging zeolitic imidazolate framework (ZIF)-derived carbons (ZDC) for the ORR using IL modification strategy. First we verified again the boosting effect of IL toward the ORR on the as-synthesized ZDC materials. The half wave potential of ORR on these ZDCs is positively shifted by up to 18 mV and their intrinsic kinetic current (@ 0.85 V) is increased by a factor of 2 after being modified with [BMMIM][NTf2]. At the same time, it is observed that the boosting effect from IL modification is highly sensitive to the exact loading amount of the IL. Exceeding a specific loading amount, however, leads to a mass transport related activity drop. Moreover, it is also unraveled that the IL takes effect by increasing electrochemically accessible surface area, as reflected by the significantly enhanced double layer capacitance of ZDCs after IL modification. These results again demonstrate the great promise of the IL modification strategy as a generic method to improve ORR catalysts, and at the same time are anticipated to form the basis for an unprecedented perspective in developing high-performing non-precious metal catalysts for low temperature fuel cell applications.

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