Elaeis guineensis Jacq.waste-derived as an supercapacitor electrode material with low cost and environmentally friendly

The increasingly rapid development of environmentally friendly porous activated carbon (AC) materials has attracted the attention of researchers. Moreover, the material can be produced from organic waste which is abundantly available. This time, porous active carbon based on green material (palm frond waste) has been successfully prepared and characterized. The application of more efficient, environmentally friendly and cost-effective, methods and production instrument has been optimized in this research. Integrated pyrolysis with carbonization (N2; 600 °C) and physical activation (H2O; 800 °C) produces activated carbon with a high purity level of up to 80 %. Through reviewing N2 gas absorption, it was confirmed that palm frond AC has a specific surface area of 356 m2 g−1, with a rough morphological structure and very rich surface nanopores. Furthermore, XRD characterization confirmed the purity of carbon through good amorphorosity properties with the presence of two wide peaks at diffraction angles of 22-24° and 42-44°. These findings show that the development and innovation of activated carbon production that is more environmentally friendly and cost-effective from palm frond waste is capable of producing active carbon with extraordinary physical characteristics. This palm tree AC has high potential for developing applications such as as an absorption material in air purifiers and water purifiers. Apart from that, these extraordinary characteristics also make palm frond AC suitable for use as electrode material in components of energy storage devices, supercapacitors with specific capacitance 86 F g−1.


Introduction
Recently, activated carbon materials applied to various electronic device components have attracted attention because they have unique geometries.In addition, its thermal stability and electrochemical conductivity are outstanding.Activated carbon materials with unique morphological pore structures have become very promising, composed of superior microstructures with tunable porosity and good electrochemical performance.The production of activated carbon with abundant pore structure has been carried out using a simple approach in the experimental stage.Precarbonization and pyrolysis are stages that can be improved so that the process of making supercapacitor electrodes becomes more environmentally friendly and cost effective.
Increasing activated carbon production in terms of equipment is carried out by replacing the use of electric ovens with energy-saving furnaces.Precarbonization using a furnace can maximize carbon production up to 200 times more than using an electric oven.In the one-stage integrated pyrolysis stage, scale-up is carried out by replacing the absorption of carbon dioxide gas (CO 2 ) into water vapor (H 2 O) to open the carbon pore structure during the physical activation process which saves costs and is environmentally friendly.In addition, to obtain uniform electrochemical performance from this lowcost activated carbon, less efficient chemical activation methods were eliminated.Based on previous research, porous activated carbon can be produced through a more complex method from biomass waste as a base material to be applied to components of energy storage devices, water purification and CO 2 gas absorption [1].The choice of biomass as a consideration for global problems in the sustainable development of active carbon needs to be considered.Palm oil is a type of plantation commodity that plays a strategic role in supporting Indonesia's economic development.As a consideration, according to data from the Central Statistics Agency (BPS), palm oil production in Indonesia is very high, reaching 45.12 million tons in 2022.Indonesia is also the largest palm oil producing country in the world with production reaching 42.5 %, followed by Malaysia, Thailand, Colombia, and Nigeria.Palm oil is a plant that produces cooking oil with quality that is recognized by the world.Apart from processing palm oil into oil, by-products are also produced from palm oil waste such as stems, empty bunches, fronds, fruit and leaves.The handling of palm oil waste has been optimized in various industrial fields as an excellent absorbent media.Referring to Ayinla Ridwan Tobi and John Ojur Dennis has prepared a 3D carbon framework using bio-palm oil waste composite base material through a series of carbonization processes.This research produces activated carbon with porosity that is accessible to charged ions which can increase specific capacitance [1].Kotchaphan Kanjana, et al considered rubber seed shell biomass as a potential carbon precursor to produce 3D porous carbon through a physical activation-carbonization process with KOH impregnation.These results also show the high electrochemical performance of rubber seed shell activated carbon as a basic material for supercapacitor electrodes [2].
Until now, research using palm frond waste as a material for making porous carbon, especially for electrodes in supercapacitor cell components, is still in the early stages (laboratory scale).Palm fronds have a characteristic dark green color and reach a size of 2 meters.Here, palm frond waste is a potential basic material because it is rich in natural fibers composed of cellulose (50 %), hemicellulose (23 %), and lignin (21.7 %), as well as high levels of carbon and oxygen which are expected to be able to provide physical properties.superior chemistry for application as a base material for porous activated carbon.Carbon-producing nanocellulose is mostly produced from plants with non-wood structures, one of which is palm fronds.The conversion of palm fronds into porous activated carbon is carried out using improved methods and tools as well as the elimination of chemical carbon synthesis, so that the process becomes simpler and more cost-effective.
The novelty of this research lies in manufacturing porous activated carbon through a scale-up approach while maintaining green technology that is energy efficient, time efficient and without the addition of expensive and dangerous chemicals.The novelty of this research is the discovery of natural precursors from palm frond waste as the basic material for carbon electrodes for components of supercapacitor energy storage devices which have the ability in terms of uniform electrochemistry, eco-friendly, low cost and sustainable energy through increased production.The emphasis of research activities is directed at green technology approaches through precarbonization and pyrolysis innovations to realize supercapacitors on a commercial scale.For the first time, we used potential biomass waste from palm fronds through improved methods (precarbonization and physical activation) as the only basic material for making active carbon through a simple synthesis, with onestage integrated pyrolysis (carbonization-physical activation) to obtain porous carbon promising.A physical activation temperature of 800 °C is provided during the pyrolysis process which contributes to controlling the optimization of pore structure formation.The specific capacitance produced from palm frond waste-based activated carbon electrodes is also supported by the interesting features of the resulting pore system and the provision of active sites between the electrode and the appropriate electrolyte during the electrochemical process.The selection of potential biomass waste precursors from palm fronds as material for making carbon electrodes is a very suitable and promising strategy as opening a new path for energy storage devices towards a commercial scale that is sustainable, renewable, environmentally friendly and cost-effective.

Materials and methods
The research method for making porous carbon electrodes based on palm frond waste is divided into several stages, namely initial preparation, precarbonization, advanced preparation, integrated pyrolysis, and characterization.Palm fronds were obtained from palm oil plantation residues in the Rumbai area, Pekanbaru, Riau.Previously, the precursor was cleaned and cut into small pieces of 5-10 cm to speed up the drying process in the sun, until the sample mass reduction was <6 %.Next, precarbonization was carried out by increasing the production scale by changing the use of electric ovens to furnaces.Typically, precarbonization is carried out using an electric oven from a temperature of 50-250 °C for 2.5 hours with a sample mass of 30 g.Meanwhile, using a modified furnace, precarbonization can be carried out with a larger amount of precursor up to 10 kg with a burning time of 1 hour to turn the sample into charcoal and soften the sample texture.Then, the carbon precursor obtained was washed using distilled water to remove residual combustion ash or the degree of acidity of the sample was neutral (pH=7).The neutral carbon is dried under the hot sun for 3 days to dehydrate the remaining water content.After that, the sample particles were ground to a micrometer scale using a mortar and ball milling tool.Smoothing with mortar is done by grinding the sample manually.Meanwhile, grinding with ball milling is carried out by utilizing the collision between carbon particles and steel balls in a vacuum.Next, uniformize the carbon particle size by sieving <60 μm.Next, the carbon powder is pyrolyzed using a one-stage integrated method with carbonization at a temperature of 30-600 °C N 2 gas and physical activation at a temperature of 800 °C H 2 O gas.Then, the sample was printed into a monolith coin shape using a hydraulic press.Next, the pH of the activated carbon sample was neutralized using 1L of distilled water using the immersion method, and dried again for characterization.

Crystallinity structure analysis
Identification of the microcrystallinity structure of palm frond activated carbon was reviewed through X-ray diffraction testing.This characterization was carried out in the diffraction angle range of 10-60° using Cu-Kα atoms as source electrons.The wavelength of the Cu atom = 1.54 Å, has almost the same value as X-rays.X-ray waves that hit the surface of solid palm frond activated carbon are scattered with a spectrum as shown in Figure 1.The results of this X-ray diffraction confirm the porous amorphous nature of palm frond active carbon which is confirmed by the presence of two sloping peaks at a diffraction angle of 2θ (22.17-24.65 and 42.35-44.61)°.The first sloping peak in the 002 plane confirms amorphous carbon with a disturbed structure.Apart from that, there were also a few sharp peaks with higher intensity, namely at angles 29.51, 32.17, 35.23, 39.28, and 47.12, which were indicated by bonds of carbon atoms with oxygen and natural elements of palm frond biomass.The XRD spectrum display of active carbon from palm fronds is in accordance with previous findings which discuss the properties of biomass-based amorphous carbon such as carbon aerogels [3] and wheat husk [4].Based on tests on the composition of active carbon, it is known that there are elements other than carbon such as Mg, Ca, and Si in very small amounts.The value d 002 = 3.65 Å is a normal value for biomass-based activated carbon materials.Meanwhile, the d 100 =1.98 obtained is in accordance with the graphin carbon value.The other lattice parameters show L c values that are smaller than L a .It has been claimed that smaller L c values can support large surface areas.Therefore, these results support the characteristics of active carbon based on palm frond biomass with high surface area values.

Morphological analysis
The appearance of the surface pore structure of the palm frond activated carbon sample was reviewed using scanning electron microscopy (SEM) with a resolution of 5000x and 40000x as shown in Figures 2a and 2b.One-stage integrated pyrolysis with N 2 carbonization at 600 °C and physical activation at 800 °C creates a regular pore structure.Using IC measure software, it is known that the sample surface pore particle size is 9-206 nm.The opening of these regular nanopores is supported by carbonization and physical activation at high temperatures with the encouragement of H 2 O vapor.At 5000x magnification (Figure 2a) the surface pore structure is displayed like chunks of solid particles.A structure like this is a natural form of activated carbon from biomass which experiences bonds breaking due to heating at high temperatures.Apart from that, the H 2 O provided is able to encourage the formation of larger pore structures which are characterized by the shape of carbon particles like broken chunks.It is even clearer when the sample is viewed at a higher resolution of 40000x (Figure 2b), with the review focused on the more regular pore microstructure.This shows larger pore particles with very rich surface pores.The available nanopores can facilitate storage space for electrically charged ions in supercapacitor electrode components.The appearance of the morphological structure obtained is similar to the pore structure of biomass-based activated carbon that has been studied previously, such as Areca catechu Husk Waste [5], and Boropukuria coal [6].

Analysis of constituent elements
The composition of the active carbon constituents of palm fronds was identified through energy dispersive spectroscopy (EDS) characterization using back scattered electron (BSE) atomic sources.This element was examined at 3000x magnification with an energy range of 0-20 keV.It is known that pure activated carbon is produced from the carbonization process of inert gas (N 2 ) in a vacuum.Where, N 2 gas facilitates the release of carbon bonds with other atoms through an evaporation process from ambient temperature (30 °C) to 600 °C using a Payuntech vacuum furnace.These results show that the sample has high carbon and oxygen contents, namely 59.90 % and 33.13 % with several other volatile elements in very small amounts.The availability of carbon and oxygen can be a combination of active carbon constituent elements which can improve the performance of the supercapacitor electrodes being made.More clarity regarding the acquisition of parameters for the constituent elements of activated carbon is shown in Figure 3.The remaining volatile elements are Mg, Si, and Ca in small percentages (4.57, 2.08 and 0.32) %.The presence of this element in biomass-based activated carbon samples is because Mg, Si, and Ca are natural elements that make up palm fronds.Several previous studies have reported the carbon content of activated carbon materials derived from other biomass such as rubber wood sawdust with (87.41 %) [7], aromatic agricultural waste (87.58 %) [8] and waste banana bract (63.87 %) [9].Physical parameters such as specific surface area, pore size and pore volume were investigated by measuring the volume of N 2 gas that could be absorbed by palm frond activated carbon under vacuum conditions at a temperature of 77.35 K. Surface area measurements using the BET method confirmed the existence of maximum micro pores and few meso pores in activated carbon surface.This is confirmed from the shape of the type IV isotherm curve with an open hysteresis loop as shown in Figure 4a.The specific surface area (SSA, multipoint BET) of palm frond AC reached 356.735 m 2 g -1 with details of microporous SSA being 304.345 m 2 g -1 and mesoporous SSA being 52.39 m 2 g -1 .The existence of a combination of micro and meso pores can support the potential of palm frond activated carbon to be applied to supercapacitor electrode components.Where, the high surface area can provide a large electrode storage medium for storing charged ions.It is known that the abundant micropores available on the surface of activated carbon can support an increase in energy density.Meanwhile, the availability of mesopores in optimal quantities and in accordance with sample conditions can contribute to increasing the power density which will facilitate smooth transport of ions to fill the electrode pores.Furthermore, it was found that the total pore volume available in palm frond AC reached 0.2096 cm 3 g -1 with V micro = 0.1555 cm 3 g -1 and V meso = 0.0541 cm 3 g -1 .The ratio of the number of pore volumes corresponds to the specific surface area value.The availability of pores in the dominant microrange is also confirmed from the measured average value of pore diameter, namely 1.175 nm.Pore size distribution is shown in Figure 4b.This physical condition of activated carbon supports its application as a supercapacitor electrode material with high absorption capacity, and can be compared with the capabilities of other biomass-based active carbons that have been studied previously such as corn straw [10], wheat straw [11], and hemp fiber [12].The electrochemical performance of palm frond waste-based carbon electrodes produced in an environmentally friendly and low-cost manner was reviewed through testing using the cyclic voltammetry method.Using two symmetrical electrodes prepared as electrical charge storage, it was tested over a voltage range of 0-1 V with a scanning speed of 1 mV s -1 .Both electrodes are in acidic conditions (1 M H 2 SO 4 , liquid) which acts as a source of electrolyte carrying electrically charged ions.Voltammetric cycling of the relationship between voltage and current resulting from the sample produces a CV curve like a distorted rectangle, (Figure 5).The shape of the CV curve for palm frond electrodes is a general representation of electrochemical measurements of the CV method for biomass carbon-based carbon electrodes.Carbonization of N 2 at 600 °C produces pure active carbon by evaporating elements other than carbon contained in it.The release of elements other than carbon leaves an empty space which is used as a storage medium on the supercapacitor electrode.Furthermore, the physical activation of H 2 O at a high temperature of 800 °C results in the development of a structure and pore size that supports access to transport of electrolyte ions carrying electrical charges.These two stages support the optimization of the specific capacitance of the carbon electrode in an environmentally friendly and cost-effective manner.In addition, the purity of the carbon and oxygen composition greatly supports the durability of the electrode.Based on the calculation of the test results using the voltammetry cycle method, the specific capacitance value produced by this electrode was 86 F g -1 with an energy density of 11.94 Wh kg -1 and a power density of 43.04 W kg -1 .This value is extraordinary for supercapacitor electrodes produced from carbon materials based on biomass waste without additional chemical and physical activating substances which are of course very environmentally friendly and low cost.Furthermore, these results can be compared with the performance of other biomass-based carbon electrodes that have been studied previously such as date stone (126.5 F g -1 ) [13], stinky bean seedpod (193 F g -1 ) [14], and torch ginger (285.89F g -1 ) [15].

Conclusion
In short, maximized production methods and materials include the selection of potential materials, no hassle, physical activation of water vapor that is environmentally friendly and low cost.The evaporation of elements other than carbon which leaves empty space and increases the carbon purity to 56.38 %.This method produces palm frond activated carbon with a BET surface area of 356.735 m 2 g -1 with a nanopore particle pore size of 1.175 nm.Next, the electrochemical capabilities such as apecific capacitance, specific energy and specific power of 89 F g -1 , 11.94 Wh kg -1 and 43.04 W kg -1 , respectively.These results show that the production of porous activated carbon based on potential biomass waste, using an environmentally friendly and cost-effective process, shows high potential for application as a carbon electrode in supercapacitor components as a renewable energy storage device.

Figure 1 .
Figure 1.X-ray diffraction pattern of palm frond activated carbon samples

Figure 2 .
Figure 2. View of the morphological structure of palm frond activated carbon samples

Figure 3 .
Figure 3. Acquisition parameters for active carbon constituents of palm fronds 3.4.N 2 gas absorptionPhysical parameters such as specific surface area, pore size and pore volume were investigated by measuring the volume of N 2 gas that could be absorbed by palm frond activated carbon under vacuum conditions at a temperature of 77.35 K. Surface area measurements using the BET method confirmed the existence of maximum micro pores and few meso pores in activated carbon surface.This is confirmed from the shape of the type IV isotherm curve with an open hysteresis loop as shown in Figure4a.The specific surface area (SSA, multipoint BET) of palm frond AC reached 356.735 m 2 g -1 with details of microporous SSA being 304.345 m 2 g -1 and mesoporous SSA being 52.39 m 2 g -1 .The existence of a combination of micro and meso pores can support the potential of palm frond activated carbon to be applied to supercapacitor electrode components.Where, the high surface area can provide a large electrode storage medium for storing charged ions.It is known that the abundant micropores available on the surface of activated carbon can support an increase in energy density.Meanwhile, the

Figure 4 .
Figure 4. (a) BET isotherm curve and (b) surface pore size distribution of palm frond activated carbon samples 3.5.Electrochemical performance analysisThe electrochemical performance of palm frond waste-based carbon electrodes produced in an environmentally friendly and low-cost manner was reviewed through testing using the cyclic voltammetry method.Using two symmetrical electrodes prepared as electrical charge storage, it was tested over a voltage range of 0-1 V with a scanning speed of 1 mV s -1 .Both electrodes are in acidic conditions (1 M H 2 SO 4 , liquid) which acts as a source of electrolyte carrying electrically charged ions.Voltammetric cycling of the relationship between voltage and current resulting from the sample produces a CV curve like a distorted rectangle, (Figure5).The shape of the CV curve for palm frond electrodes is a general representation of electrochemical measurements of the CV method for biomass carbon-based carbon electrodes.Carbonization of N 2 at 600 °C produces pure active carbon by evaporating elements other than carbon contained in it.The release of elements other than carbon leaves an empty space which is used as a storage medium on the supercapacitor electrode.Furthermore, the physical activation of H 2 O at a high temperature of 800 °C results in the development of a structure and pore size that supports access to transport of electrolyte ions carrying electrical charges.These two stages support the optimization of the specific capacitance of the carbon electrode in an environmentally friendly and cost-effective manner.In addition, the purity of the carbon and oxygen composition greatly supports the durability of the electrode.Based on the calculation of the test results using the voltammetry cycle method, the specific capacitance value produced by this electrode was 86 F g -1 with an energy density of 11.94 Wh kg -1 and a power density of 43.04 W kg -1 .This value is extraordinary for supercapacitor electrodes produced from carbon materials based on biomass waste without additional chemical and physical activating substances which are of course very environmentally friendly and low cost.Furthermore, these results can be compared with the performance of other biomass-based carbon electrodes that have been studied previously such as date stone (126.5 F g -1 )[13], stinky bean seedpod (193 F g -1 )[14], and torch ginger (285.89F g -1 )[15].

Figure 5 .
Figure 5. Electrochemical performance of palm frond activated carbon samples using the CV method

Table 1 .
Performance of palm frond based carbon electrodes and comparison with different biomass based electrodes.