Characterization and Analysis of Activated Carbon from Coconut Shells Applied to Supercapacitors

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Sainstek: Jurnal Sains dan Teknologi

Vol 15 No 2, December 2023 ISSN: 2085-8019 (p), ISSN: 2580-278x (e)

128

Characterization and Analysis of Activated Carbon from Coconut Shells Applied to Supercapacitors

Andi Ikhtiar Bakti

¹

*, Handy Indra Regain Mosey

¹

, Jumriadi

¹

1Physics Department, Universitas Sam Ratulangi Jl. Kampus UNSRAT Kleak Kota Manado, Indonesia

*email: [email protected]

Article History

Received: 7 October 2023 Reviewed: 20 November 2023 Accepted: 27 December 2023 Published: 31 December 2023

Key Words

Activated carbon; Coconut shells; Supercapacitor;

Conductivity.

Abstract

Activated carbon is used materials as an electrode for supercapacitors. The aim of this research is to characterize and analyze activated carbon for results with high specific surface area, chemical resistance, electrical conductivity, and affordability. The pyrolysis technique is used in the activation process to remove water content and achieve optimal carbonization at an activation temperature of 600°C. For chemical activation, the carbon is immersed in 10% KOH and 10% Na2CO3 activating agents. The X-RD results in crystalline phases of graphite at peaks 25° and 44°, showing diffraction peaks of carbon and graphite. SEM characterization microstructure morphology at 3000 times magnification, with a 10 µm image size, the formation of porosity that carbon activation. The iodine adsorption measurement KOH- activated carbon sample is 630.70 mg/g, and Na2CO3 activation at 567.89 mg/g. Conductivity measurement results indicate that the conductivity values of activated carbon with the addition of KOH and Na2CO3 activation, measuring 1724.10 S/m and 1660.60 S/m.

INTRODUCTION

One of the energy storage media currently being intensively investigated is capacitors and supercapacitors.

Supercapacitors, also known as electrochemical capacitors, are electrical double layers in the form of electrodes separated by a separator (Nuradi et al., 2022).

The aim of this research is to characterize and analyze activated carbon for results with high specific surface area, chemical resistance, electrical conductivity, and affordability.

Supercapacitors store energy depending on the electrostatic charge that accumulates at the electrochemical double- layer capacitor, such as carbon. The energy storage mechanism is also due to the

reversible redox reactions of transition metal oxides and reversible doping/de-doping in conducting polymers or hybrid capacitors (Rustamaji et al., 2022). Batteries, supercapacitors and fuel cells belong to the system of electrochemical energy storage that forms an integral part of the renewable energy group. Although the battery is the number one choice as a storage device, nonetheless, much attention is currently being paid to supercapacitors due to the high power density that is multifold of that of batteries, high specific capacitance and extended cycle life (Abioye & Ani, 2020).

Carbon and carbon-based electrodes have gained widespread applications in various energy storage systems because they are low- cost and have thermochemical stability,

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processability, structural tenability, and

textural characteristics to achieve the necessities of the particular applications (Ahmad et al., 2023). Compared to conventional batteries or capacitors, the charging time of a supercapacitor is much less and can discharge like a regular battery.

Comparatively, these are lightweight and environmentally friendly (Gautham Prasad et al., 2019).

Coconut shells are rich in cellulose, containing carbon that makes them a viable source of raw material for producing activated carbon. The process of creating activated carbon from coconut shells involves pyrolysis, wherein the coconut shell is converted into charcoal, followed by an activation process. The activation process comprises both physical and chemical activation methods. Physical activation entails subjecting the material to high temperatures (400-1000°C) through carbonization. On the other hand, chemical activation involves immersing the coconut shell charcoal in a chemical solution with specific concentrations of substances like ZnCl2, Na2CO3, KOH, or KCl (Tumimomor & Palilingan, 2018). Given this background, there is a need to research utilizing activated carbon derived from coconut shell waste as an electrode material in supercapacitors. The research will involve characterizing the activated carbon using XRD and SEM-EDX instruments while assessing its iodine adsorption capacity, conductivity, and capacitance through various tests (Bakti & Gareso, 2018) (Bakti et al., 2018).

METHOD Raw Material

The coconut shells were cleaned with distilled water several times to remove dust and dirt. Afterward, the coconut shell samples were dried in an oven at 100°C for 24 hours to eliminate surface moisture, and then ground to the desired size.

Activated Carbon

The coconut shells were activated using physical activation by placing them in a

pyrolysis reactor heated by an electric tube furnace. The reactor was then heated to a temperature of 600°C and held for one hour.

After the activation process was completed, the activated carbon was cleaned with distilled water and dried in an oven at 100°C for thirty minutes. The coconut shell carbon that has been pyrolyzed at 600°C was soaked in a 10%

KOH and 10% Na2CO3 solution, and then stored at room temperature for 24 h. After the activation process was completed, the activated carbon was cleaned with distilled water and dried in an oven at 100°C for 30 m.

Following that, the carbon was sieved using ASTM Standard Test Sieves with a mesh size of 100-200 Mesh. The sieve model used consisted of three layers of sieves. The sieved samples were then characterized and analyzed.

Iodine Adsorption Test

Involved weighing 2 grams of activated carbon and mixing it with 10 ml of 0.1 N iodine solution. The mixture was shaken using a shaker for 15 minutes. Afterward, it was transferred to a centrifuge tube until the activated carbon settled, then 10 ml of the liquid was taken and titrated with 0.1 N sodium thiosulfate solution. If the yellow color in the solution starts to fade, add 1%

amylum solution as an indicator. Titrated again until the dark blue color turned clear.

The formula for calculating iodine adsorption capacity is as eq.1.

𝐼 =(𝑉1𝑥𝑁1−𝑉2𝑥𝑁2)𝑥126,9𝑓𝑝

𝑤 (1)

where I is the adsorbed iodine in mg/g, V1 is the volume of iodine solution used for analysis in ml, V2 is the volume of sodium thiosulfate solution required in ml, N1 is the normality of iodine in N, N2 is the normality of sodium thiosulfate in N, W is the weight of the sample in g, and fp is the dilution factor.

Creation of Parallel Plate Capacitors Parallel plate capacitors are used for measuring electrical conductivity and dielectric constant of activated carbon. The first step involves creating capacitor plates from PCB boards measuring (3x3) cm. The

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PCB plates cut to the specified size, are placed

into a rectangular container with a 6 mm spacing between the plates. Design the parallel plates using the PCB boards as shown in the image. Next, apply adhesive to the PCB

to affix them to the container walls. Connect the designated terminal parts with connecting cables by soldering. Seal the top of the container with tape to make it airtight.

Figure 1. The XRD spectrum of activated carbon in crystalline phases of graphite

Conductivity Test

Activated carbon 1.5 grams with concentrations of 10% KOH and 10% Na2CO3

activator were placed into the rectangular container with PCB measuring 3.0x3.0 cm and a gap distance of 6.0 mm. Subsequently, electrical property testing was conducted, including resistance measurement using the Sanfix BM4070 LCR meter. The resistance mode R on the LCR meter was activated, and each electrode was connected to the plates.

The input frequency used for this measurement was 10 kHz, and the resistance value displayed on the LCR meter was recorded. The obtained resistance values from the measurements can then be used to determine the electrical conductivity using the eq. 2

𝜎 = ^𝐿

𝐴𝑅 (2)

where σ is the electrical conductivity in S/m, L is the length of the cross-section in m, A is the cross-sectional area in m², and R is the resistance in Ω.

RESULTANDDISCUSSION XRD Analysis

The XRD spectrum of activated carbon illustrates the presence of several

crystalline phases, primarily graphite, around the peaks at 24° and 44° for the (002) and (101) hkl planes (see Figures 1). These two broad diffraction peaks can be associated with the presence of both carbon and graphite, indicating signs of crystalline carbon structure formation, resulting in improved layers (Rani et al., 2014). Both activated carbon samples display two broad diffraction peaks located at 2θ = 40°-50°, revealing an irregularly stacked amorphous structure attributed to carbon rings and beneficial in producing adsorbed pores.

For unladen carbon, sharp peaks at 44° are observed, caused by the indicated K and Na species used during the activation process (Hidayu & Muda, 2016).

The findings of this activated carbon align with prior studies by Kushwaha et al. and Rani et al. (Kushwaha et al., 2013). Post-pyrolysis, both samples exhibit two broad diffraction peaks associated with the presence of carbon and graphite (Hidayu et al., 2013).

SEM Analysis

Scanning Electron Microscopy (SEM) is used to observe the physical morphology of sample surfaces. Shows the SEM morphology (see Figure 2) of

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microstructures at a magnification of 3000

times, with a picture size of 10 µm, revealing the formation of pores and porosity, explaining the successful carbon activation results from the active carbon microstructure with KOH and Na2CO3. Demonstrate that the activation stage produces an extensive external surface with sufficiently sized pores (Xiong et al., 2023). High porosity is observed on the external surface of KOH and Na2CO3.

SEM morphology illustrates that the pores are visible on the KOH and Na2CO3 samples, indicating a successful active carbon process (Pradhan, 2011). Although the cavities are inhomogeneously distributed, still this type of open structure can be successfully used for energy storage applications (Ahmed et al., 2018). The difference between the two images is that the porosity of the activation KOH is more clear than the Na2CO.

Figure 2. Morphology on the surface of activated carbon magnification of 3000x (a) AC KOH (b) AC Na2CO3

Iodine Adsorption and Conductivity The results of the iodine adsorption test (see Table 1) show that the maximum iodine adsorption capacity is found in KOH- activated carbon, at 630.70 mg/g. Meanwhile, the minimum iodine adsorption capacity is found in Na2CO3-activated activated carbon, at 567.89 mg/g. This is due to the surface area of pores being a critical parameter in determining the quality of activated carbon as an adsorbent. The surface area of pores is one of the factors influencing the adsorption capacity of an adsorbent. The reactivity of activated carbon can be observed through its ability to adsorb substrates. This adsorption ability is demonstrated by the iodine number, which indicates how much the adsorbent can adsorb iodine. The higher the iodine number, the greater the adsorption capacity of the adsorbent.

The results of the conductivity measurements indicate that the conductivity values of activated carbon tend to increase with the addition of KOH and Na2CO3

activation, with values of 1724.10 S/m for AC KOH and 1660.60 S/m for activated carbon with Na2CO3. This may be due to the reduction of impurities such as water content, volatile components, and minerals, resulting in an increase in electrical conductivity in KOH-activated AC. According to theory, the conductivity values obtained approach the conductivity of graphite, which is approximately 3400 S/m (Ahmed et al., 2018).

The one-step KOH and Na2CO3 impregnation turned out to be more suitable for producing a combination of micro- and mesopores on activated carbon monolith which contributed to the high capacitive properties (Taer et al., 2020).

Table 1. Results of iodine adsorption and conductivity testing

Sample (mL/bar) Iodine Absorption Test (mg/g) Conductivity (S/m)

AC KOH 630,70 1724,10

AC Na2CO3 567,89 1666,60

a b

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132 Characterization and analysis of

the

XRD spectrum of activated carbon illustrate the presence of several crystalline phases, primarily graphite, around the peaks at 24° and 44° for the (002) and (101) hkl planes. , indicating signs of crystalline carbon structure formation, resulting in an n improved layer. SEM morphology of microstructures at a magnification of 3000 times, with a picture size of 10 µm, revealing the formation of pores and porosity, explaining the successful carbon activation results from the active carbon microstructure with KOH and Na2CO3. SEM morphology illustrates that the pores are visible on the KOH and Na2CO3

samples, indicating a successful active carbon process. Although the cavities are inhomogeneously distributed, still this type of open structure can be successfully used for energy storage applications. The maximum iodine adsorption capacity is found in KOH- activated activated carbon, at 630.70 mg/g.

Meanwhile, the minimum iodine adsorption capacity is found in Na2CO3-activated activated carbon, at 567.89 mg/g. This may be due to the reduction of impurities such as water content, volatile components, and minerals, resulting in an increase in electrical conductivity in KOH- activated AC. According to theory, the conductivity values obtained approach the conductivity of graphite, which is approximately 3400 S/m.

Conductivity measurement results indicate that the conductivity values of activated carbon tend to increase with the addition of KOH and Na2CO3 activation. Activated carbon produced from coconut shells is a conductor material. The one-step KOH and Na2CO3

impregnation turned out to be more suitable for producing a combination of micro- and mesopores on activated carbon monolith which contributed to the high capacitive properties.

ACKNOWLEDGEMENT

The researcher expresses gratitude to LPPM Unsrat and funded by RDTU3 of the Unsrat scheme in 2023 contract number 906/UN12.13/LT/2023

for this research, as well as to the parties assisting the integrated

researchers who aided in this study.

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