ECS Electrochemistry Letters

A novel electrochemically induced method for ammonia synthesis (eU2A) on demand from urea in alkaline media was demonstrated. A Nickel based electrode was employed as the active catalyst. The effective rate of ammonia generation of the eU2A process at 70°C is ∼28 times higher than the thermal hydrolysis (THU) of urea. The eU2A operates at lower temperature (55% lower) and pressure (6 times lower) than the THU; this could lead to significant energy savings. The process finds applications on selective catalytic reduction (SCR) for the removal of nitride oxide from combustion systems (e.g., diesel vehicles, power plants, etc.).

Lithium-ion batteries are prone to failure at low temperatures and dendrite growth during charging is one suspect. We attempt to understand lithium dendrite growth by observing their number, initiation time and growth rate at ambient and sub-ambient temperatures: −10°C, 5°C, and 20°C using an in-situ optical microscopy cell (Li⁰|Li⁰). We find that while dendrites initiate quickly at −10°C, the cells at 5°C short-circuit most rapidly due in part to a favorable morphology at this temperature. The experimental approach has broad applicability to other electrochemical energy storage technologies where mass transport limitations are present at low temperatures, particularly Li-air, Li-S, and Zn-air batteries.

We synthesized a copper rubeanate metal organic framework (CR-MOF) which has the potential to improve the catalytic activity of electrochemical reduction of CO₂ due to its characteristics of electronic conductivity, proton conductivity, dispersed reaction sites, and nanopores. Synthesized CR-MOF particles were dropped on carbon paper (CP) to form a working electrode. The onset potential for CO₂ reduction of a CR-MOF electrode was about 0.2 V more positive than that observed on a Cu metal electrode in an aqueous electrolyte solution. Our analysis of the reduction products during potentiostatic electrolysis showed formic acid (HCOOH) to be virtually the only CO₂ reduction product on a CR-MOF electrode, whereas a Cu metal electrode generates a range of products. The quantity of products from the CR-MOF electrode was markedly greater (13-fold at −1.2 V vs. SHE) than that of a Cu metal electrode. Its stability was also confirmed.

This study examined the feasibility of using a sintered Ag/AgCl electrode as a combined reference (RE) and counter electrode (CE) for polarization measurements in thin film solutions. The combined electrode provided uniform current distribution without altering the thin film electrolyte composition. This approach avoids the problems of distorted current distributions inherent in the use of reference and counter electrodes positioned away from the working electrode (WE) under thin film conditions.

Two procedures to introduce a lithium metal reference electrode into commercially manufactured lithium-ion pouch cells (Kokam SLPB 533459H4) are described and compared. By introducing a stable reference potential, the individual behavior of the positive and negative electrodes can be studied in operando under normal cycling. Unmodified cells and half-cells made from harvested electrode material were cycled under identical conditions to the modified cells to compare capacity degradation during cycling and thus validate each modification procedure for degradation testing. A configuration that did not affect the performance of the cell over 20 cycles was successfully developed.

Electroplating of aluminum (Al) on silicon (Si) substrates has been demonstrated in an above-room-temperature ionic liquid for the metallization of wafer-Si solar cells. The electrolyte was prepared by mixing anhydrous aluminum chloride and 1-ethyl-3-methylimidazolium tetrachloroaluminate. The plating was carried out by means of galvanostatic electrolysis. The structural and compositional properties of the Al deposits were characterized, and the sheet resistance of the deposits revealed the effects of pre-bake conditions, deposition temperature, and post-deposition annealing conditions. It was found that dense, adherent Al deposits with resistivity in the high 10⁻⁶ Ω-cm range can be reproducibly obtained directly on Si substrates.

Polyacrylic acid (PAA) as a binder in the aqueous solvent is applied in the preparation of sulfur cathode for lithium-sulfur battery. Electrochemical performances are investigated by a charge-discharge cycle test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV and EIS tests indicate that the PAA sulfur cathode has smaller resistance and better kinetics characteristics than that of the poly(vinylidene fluoride) (PVDF) sulfur cathode using PVDF as a binder in N-methy-2-pyrrolidone (NMP) solvent. The charge-discharge tests show that the discharge capacity and the coulombic efficiency of the PAA sulfur cathode are 325 mAh g⁻¹ and 89.5% at the 50th cycle at the current density of 335 mA g⁻¹. Compared with the PVDF sulfur cathode, the PAA sulfur cathode shows considerably a better cyclability. These results show that the PAA binder has great potential for lithium-sulfur battery applications.

A P2-layered oxide using copper as the active redox metal has been discovered. It has a composition of Na_⅔Cu_⅓Mn_⅔O₂, and can withstand a thousand cycles, maintaining 61% of its original capacity. We demonstrate that copper can enable not only high voltage, but also excellent stability. This work opens up a new avenue of oxide design for high energy, cost effective battery systems.

In situ X-ray diffraction (XRD) technique combined with electrochemical analysis was used for investigating the structural changes of nickel hydroxide catalysts in alkaline media and to provide a better understanding of the reaction mechanism of urea electrooxidation for applications in hydrogen production, fuel cells, and sensors. The evolution of XRD patterns reveals Ni(OH)₂ is electrochemically oxidized to NiOOH at cell voltages from 1.2 to 1.6 V. The generated NiOOH reacts with urea and thus is reduced back to Ni(OH)₂, while urea is concurrently oxidized. The technique can be extended to other electrochemical systems (alkaline rechargeable batteries, supercapacitors, and fuel cells).

A CeO₂ supported membrane electrode assembly (MEA) was fabricated by hot-pressing CeO₂-coated electrodes and a PFSA ionomer membrane. Upon application of a combined chemical and mechanical accelerated stress test (AST), the CeO₂ supported MEA showed six times longer lifetime and 40 times lower fluoride emission rate than a baseline MEA without cerium. The membrane in the CeO₂ supported MEA effectively retained its original thickness and ductility despite the highly aggressive AST conditions. Most of the cerium applied on the anode migrated into the membrane and provided excellent mitigation of joint chemical and mechanical membrane degradation.