Synthesis of magnetic activated carbon-supported cobalt(II) chloride derived from pecan shell (Aleurites moluccana) with co-precipitation method as the electrode in supercapacitors
Muhammadin Hamid
a,⇑, Susilawati
a, Suci Aisyah Amaturrahim
b, Ivi Briliansi Dalimunthe
a, Amru Daulay
caDepartment of Physics, Universitas Sumatera Utara, Medan 20155, Indonesia
bDepartment of Chemistry, Universitas Sumatera Utara, Medan 20155, Indonesia
cResearch Center for Mining Technology, National Research and Innovation Agency (BRIN), Jl. Ir. Sutami, Km. 15, Tanjung Bintang, South Lampung, Lampung Province, Indonesia
a r t i c l e i n f o
Article history:
Received 22 February 2023 Revised 14 April 2023 Accepted 16 April 2023 Available online 20 April 2023
Keywords:
Activated carbon Pecan shell Cobalt(II) chloride Electrode Supercapacitors
a b s t r a c t
The synthesis of materials on magnetic activated carbon is of concern, with a simple and environmentally friendly. The research used pecan shell (Aleurites moluccana) as a carbon source. The breakthrough made in this research is to make magnetic activated carbon electrodes in supercapacitors. Obtained on the XRD diffractograms show the graphite lattice, respectively. Also, a sharp, narrow peak is seen at 2h= 26°in the carbon samples spectrum, showing a highly graphitized fraction. FESEM-EDX showed AC20/80 that the shape of the particles was like plates indicating that the particles had been formed. AC80/20 is the surface morphology in which particles with irregular shapes indicate that particles have been formed, where the shape of the particles is irregular. The composition between C and O is also balanced. AC80/20 has lower Co content than AC20/80, AC40/60, AC60/40, and AC50/50 and it appears that AC80/20 is better than the others. The magnitude of the coercivity states that AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 are strong magnets. The lower the value of the open circuit potential, it will show electrochemical stability.
The Nyquist plots of magnetic activated carbon show a straight vertical indicating the process of charge transfer resistance at the low electrode. Obtained specific capacitance AC80/20 at 150F/g.
Ó2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Because of high specific capacitance, superior cycle perfor- mance, lengthy service life, quick rate of charging and discharging, safety during use, and ease of maintenance, supercapacitors have attracted much interest[1–3]. Supercapacitors have been used in many areas, like hybrid cars, power tools, and rail transit [4–6].
Based on how it stores charge, supercapacitors can be divided into two categories: electric double-layer capacitors and pseudo- capacitors [7]. Supercapacitor electrodes are mainly constructed of carbon-based materials, conductive polymers, and metal com- pounds [8]. Due to low-conduct electricity, high cost and poor cycle performance, metal compounds and conductive polymers are unacceptable[1,9].
Activated biomass carbon compounds often do not exhibit sig- nificant improvements in electrochemical performance. It is because low mesoporosity and weak conductivity could be con- strained by electron transfer and ion transport[10]. Finding new
ways to adjust the electronic conductivity and porous architectures for supercapacitors is still challenging because of how the activa- tors operate. It has been claimed that FeCl3can support the graphi- tization process during biomass pyrolysis. The graphitization and activation processes may coincide if FeCl3and ZnCl2are utilized as activators[11]. Therefore, graphitic porous carbon, which typi- cally has strong conductivity, should be produced via bimetallic activation. During pyrolysis, biomass can also produce unique nanoparticles when exposed to a metal salt like MgCl2[12,13].
Several studies have worked on carbon electrode materials and made many carbon materials, such as activated carbons[14], gra- phene[15], and carbon nanotubes[16]. Carbon nanotubes and gra- phene, for example, are hard to make and expensive, which makes it hard to make large amounts of them. Activated carbons made from cheap and plentiful biomass have been suggested as possible electrode materials because they are cheap, renewable, and good for the environment [14]. Also, activated carbons from biomass work well as supercapacitor electrodes because they have a high specific surface area and a unique porous structure. Biomass mate- rials can make hierarchically porous carbons with a large surface area and functional groups containing oxygen and nitrogen[17].
https://doi.org/10.1016/j.mset.2023.04.004
2589-2991/Ó2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
⇑Corresponding author.
E-mail address:[email protected](M. Hamid).
CHINESE ROOTS GLOBAL IMPACT
Contents lists available atScienceDirect
Materials Science for Energy Technologies
j o u r n a l h o m e p a g e : w w w . k e a i p u b l i s h i n g . c o m / e n / j o u r n a l s / m a t e r i a l s - s c i e n c e - f o r - e n e r g y - t e c h n o l o g i e s
The nature of biomass materials makes it possible to get unique porous properties that can be used to make electrode materials [18,19]. Biomass carbons can be made with porous and intercon- nected structures[20]. It makes it easier for ions to move through the carbon and electrolytes to get into it. Due to biomass materials’
complex structures and compositions, many problems remain when making active carbons with high electrochemical perfor- mance efficiently and effectively.
Pecan shells (Aleurites moluccana), which are organic waste, cause environmental problems. Many people do not know the ben- efits of hazelnut shells, and the waste is thrown away. Disposal of hazelnut shell waste can endanger pedestrians because the broken hazelnut shells are sharp and hard[21]. This hard waste texture can be used as a coarse aggregate mixture to manufacture concrete [22,23]. Another solution in utilizing candlenut shells is to make charcoal briquettes to manufacture paint, varnish, ink, soap, and hair oil to manufacture activated carbon[24]. Recent studies have succeeded in processing pecan shells into carbon for applications in biodiesel[25], photocatalysts, biomass[26], and supercapacitors [27].
Several methods for the synthesis of activated carbon from pecan shells have been researched, such as steam activation[28], oxidation [29], and pyrolysis [30]. This study used pecan shells (Aleurites moluccana) with a co-precipitation method to synthesize magnetic activated carbon-supported cobalt(II) chloride from bio- mass for the application electrode in supercapacitors. XRD, FESEM- EDX, VSM, and N2adsorption characterized the obtained activated carbon. For application, electrodes in supercapacitors were used CV, EIS, and GCD.
2. Materials and method 2.1. Materials
Pecan shells (Aleurites moluccana) were obtained from Deli Ser- dang, Indonesia. Distilled water was purchased CV. Rudang Jaya.
Cobalt(II) chloride (CoCl2 98 wt%), Sodium hydroxide (NaOH 98 wt%), acetic acid (CH3COOH 98 wt%), ethanol (EtOH 98 wt%), Sodium sulfate (Na2SO4 98 wt%), acetylene black, polytetrafluo- roethylene, and nickel foil were purchased by Sigma-Aldrich. All the chemical reagents as approved without additional purification.
2.2. Preparation of magnetic activated carbon
The raw material for pecan shells (Aleurites moluccana) contains a chemical composition of 74.3% C, 21.9%, 0.2% Si, 1.4 % K, 0.5% S, and 1.7% P [31–33]. The high carbon content makes it potential to synthesize magnetic activated carbon. First, wash the pecan shells using distilled water, then dry them in the sun for 4 h. The dried pecan shells were mashed using a hammer mill, and the pecan shells were crushed using a ball mill. The sample prepara- tion begins by weighing each fine powder of pecan shells and CoCl2
with a predetermined composition (variation powder pecan shells:
CoCl2that were 20:80, 80:20, 40:60, 60:40, and 50:50). Then, dis- solved in a beaker glass with 15 mL of the acetic acid solution and stirred for 1 h at a speed of 500 rpm and a temperature of 80°C.
After the pecan shells dissolved, CoCl2was added until the two ingredients were homogeneous. After that, prepare 150 mL of dis- tilled water in the next beaker. Then add NaOH 2 M and stir at a speed of 700 rpm for 30 min. After the NaOH becomes a solution, it is slowly added to the homogeneous with CoCl2solution and stir- red for 3 h. After 3 h, the solution was washed 10 times to lower the pH to 7 (the fifth and eighth washings used 100 mL of ethanol).
Then the samples were dried in an oven for 8 h at 80°C to form a powder. The sample powder was dried at 100 °C for 2 h. The
obtained powder is ground using a mortar. The 5 samples were named AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50, where 20/80, 80/20, 40/60, 60/40, and 50/50 refer to variation powder pecan shells: CoCl2. The scheme of preparation of magnetic acti- vated carbon can be seen inFig. 1.
2.3. Characterization
X-ray diffraction (XRD) was also carried out in a 2h range between 10°and 90°(voltage: 40 kV; current: 40 mV; wavelength:
0.154 nm; step size: 6°min 1; integration time: 790 s). Field emis- sion scanning electron microscopy- energy dispersive X-ray (FESEM-EDX JEOL JED-2300) operates at 15 kV to investigate the morphology, elemental mapping, and analyze the element (wt%).
Vibrating sample magnetometer (VSM VSM250 - P2F). N2adsorp- tion carried out quantachrome Instruments, NOVA touch 4LX). The Barret–Joynerv–Halenda (BJH) method obtained the pore size distribution.
2.4. Fabrication of the electrode and electrochemical measurements
Three-electrode device was used to test the electrochemical performance of prepared electrodes with activated carbon samples using cyclic voltammetry (CV), electrochemical impedance spec- troscopy (EIS), and galvanostatic charge discharge (GCD) on the electrochemical workstation (Corrtest) with 1 M Na2SO4solution.
In the three-electrode system, the counter electrode was a plat- inum plate, and the reference electrode was a calomel electrode.
The working electrode was made from activated carbon by follow- ing the steps below. First, activated carbon, acetylene black, and polytetrafluoroethylene with variation 85:10:5 were mixed in ethanol to make a slurry. The slurry was then put into a nickel foil and dried in a 105°C oven for 12 h. The working electrode was put into a 1 M Na2SO4solution for 24 h.
Fig. 1.The scheme of preparation of magnetic activated carbon.
3. Results and discussions 3.1. Analysis of XRD
XRD diffractogram patterns were made to study the crystal structure of magnetic activated carbon materials can be seen in Fig. 2. In the XRD diffractogram of the samples, two diffraction peaks are at 2h= 22°and 2h= 42°. These are the diffractions of the (0 0 2) and (1 0 1) planes of the graphite lattice, respectively [34–36]. Noting that these two diffraction peaks are low in height and wide, which shows that graphitic carbons were formed during the activation process, is essential. Also, a sharp, narrow peak is seen at 2h = 26° in the spectrum of the carbon samples, which shows that a highly graphitized fraction is present[37,38]. So, it is clear that the samples were amorphous carbons with some gra- phitic structures[39].
3.2. Analysis of FESEM-EDX
FESEM-EDX characterization was carried out to determine mor- phology and elemental composition. The element can be analyzed inFig. 3. Morphological observations inFig. 3a showed AC20/80 that the shape of the particles was like plates indicating that the particles had been formed. Changes on the surface of these parti- cles occur due to the combination ofAleurites Moluccanapowder with Cobalt Chloride.Fig. 3b showed AC80/20 the surface morphol- ogy in which particles with irregular shapes indicate that particles have been formed, where the shape of the particles is irregular like plates.Fig. 3c,d showed AC40/60 and AC60/40 that the material is not evenly distributed and is still porous between particles. The reason for the occurrence of pores between particles is that there has not been perfect diffusion between particles.Fig. 3d showed AC50/50 the porous carbon surface looks uneven and untidy. In the activation process, these structures and pores are formed [40,41].
Elemental analysis (wt%) from the EDX spectra can be seen in Fig. S1,Table 1and Elemental mapping can be seen inFig. S2. It can be seen that AC20/80 has a lower C composition than O. The Co composition is also high. It shows that the activated carbon that is formed is not perfect. The AC80/20, AC40/60, AC60/40, and AC50/50 have balanced C and O compositions. It shows that the activated carbon that is formed is considered successful. However, due to the addition of Co, it is hoped that the activated carbon formed will have a low Co content. Because the Co content in acti- vated carbon affects the electrochemical performance of the super- capacitor electrode [42,43]. AC80/20 has lower Co content than AC20/80, AC40/60, AC60/40, and AC50/50. The composition between C and O is also balanced. Even though the amount of C is more than O, the bond between C occurs, and no unbonded O exists[44]. Based on SEM images and EDX spectra. It appears that AC80/20 is better than the others.
3.3. Analysis of VSM
VSM is a tool used to measure magnetic properties. By using VSM, the magnetic properties are described in the form of a hys- teresis curve. From the hysteresis curve, the magnitude of the mag- netic properties in coercivity, remanence, and saturation Fig. 2.XRD diffraction of magnetic activated carbon.
Fig. 3.SEM images of (a) AC20/80, (b) AC80/20, (c) AC40/60, (d) AC60/40, and (e) AC50/50.
magnetization will be obtained due to changes in the external magnetic field [45,46]. The results of the hysteresis curve of the VSM can be seen inFig. 4, and the analysis data inTable 2show that saturation magnetization, remanence, coercivity, and H max values are obtained. The coercivity value of a magnet is more than 10 Oe, and it is to be a strong magnet (hard magnetic). However, intrinsic properties such as crystal structure cannot always deter- mine the magnitude of the coercivity[47,48]. Extrinsic properties such as grain size, secondary phase (impurities), and morphology can also determine coercivity. Coercivity is used to distinguish between hard magnets and soft magnets. The greater the coercivity force, the harder the magnetic properties. Materials with high coercivity do not easily lose magnetism[49]. Based on the table, the coercivity values for each are 381.03 Oe, 1075.96 Oe, 837,28 Oe, 1019.78 Oe, and 770.00 Oe. The magnitude of the coercivity states that AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 are strong magnets.
3.4. Analysis of N2adsorption
N2adsorption magnetic activated carbon can be seen inTable 3.
The BET Surface area of AC20/80, AC80/20, AC40/60, AC60/40, and
AC50/50 were 14.88 m2g 1, 13.43 m2g 1, 59.86 m2g 1, 24.20 m2g 1, and 24.93 m2g 1. It can be seen that the AC80/20 has the lowest surface area compared to the others. Shows that the small addition of CoCl2causes a lower surface area. However, the highest surface area is AC40/60, where CoCl2is not higher than AC20/80. It Table 1
The component ratio magnetic activated carbon by EDX spectra of C, O, and Co.
Sample Element Element (Wt%)
AC20/80 C 28.58
O 54.07
Co 15.68
AC80/20 C 56.30
O 39.30
Co 1.60
AC40/60 C 51.53
O 41.22
Co 5.24
AC60/40 C 43.76
O 44.86
Co 9.79
AC50/50 C 43.72
O 43.33
Co 10.61
Fig. 4.VSM curve magnetic activated carbon of (a) external field and (b) specific magnetic moment.
Table 2
Parameters of the magnetic properties of activated carbon.
Sample The saturation magnetization (em/g) remanence (emu/g) Coercivity (Oe) H Max
(kOe)
AC20/80 1480.09 61.86 381.03 20.30
AC80/20 222.72 56.32 1075.96 20.24
AC40/60 767.13 50.22 837.28 20.22
AC60/40 458.59 46.61 1019.78 20.28
AC50/50 671.18 46.81 770.00 20.30
Table 3
Physical properties of magnetic activated carbon.
Sample BET surface area (m2g 1) Average pore size (nm)
AC20/80 14.88 3.8
AC80/20 13.43 3.9
AC40/60 59.86 3.2
AC60/40 24.20 3.1
AC50/50 24.93 2.9
Fig. 5.CV curve magnetic activated carbon of relationship potential with current density.
shows that a large number of CoCl2 ratios causes a low surface area, but the correct addition of CoCl2 can create a high surface area. It aligns with Tanget al.’s research on mesoporous carbon and the results that adding CoCl2increases the surface area[50].
Pore sizes of AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 were 3.8 nm, 3.9 nm, 3.2 nm, 3.1 nm, and 2.9 nm. It shows AC80/20 has the largest pore size of the others. It shows that add- ing CoCl2can reduce the formation of pore size. Zhenget al. also conducted research related to pyrolysis by adding CoCl2 and showed that CoCl2could reduce pore size[51].
3.5. Analysis of CV
CV curve activated carbon of relationship potential with current density and time with current density can be seen inFig. 5. For activated carbon, the redox peaks were easy to see. The reversible redox reaction between the active electrode materials and the elec- trolyte was thought to be responsible for the activated carbon’s good redox behavior. Due to the polarization effect and electron transfer rates on the carbon surface, the results got stronger as the scan rate and peak shifted toward positive and negative poten- tials [52]. The chemical composition and shape of the activated carbon in supercapacitors were strongly linked to improved elec- trochemical behavior.
The relationship between time with current density provides information about the electrolyte solution with charge transfer
barriers in the electrolyte. There was an increase in current density in the second peak, but at the third peak, a drastic decrease. It is due to the difficulty of penetrating the electrical signal into the deeper pores and smaller particles, resulting in a longer transfer of electrons in the holes and a higher resistance.
The parameter of the specific capacity and open circuit from cyclic potential voltammetry can be seen inTable 4. It can be seen that AC80/20 has a higher capacitance compared to AC20/80, AC40/60, AC60/40, and AC50/50. It shows that the electrochemical ability of AC80/20 is better than others. An open circuit potential indicates it. An open circuit potential is established between the working electrode (activated carbon) and the environment con- cerning a reference electrode, which will be placed in the elec- trolyte close to the working electrode. The lower the value of the open circuit potential, it will show electrochemical stability. There- fore it was found that AC80/20 has good electrochemical capabili- ties[53].
3.6. Analysis of EIS
EIS test to determine resistance to electrochemical processes using magnetic activated carbon. The Nyquist plots can be seen inFig. 6. The Nyquist plots of magnetic activated carbon show a straight vertical indicating the process of charge transfer resistance at the low electrode. AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 show no difference in charge transfer resistance. How- ever, AC80/20 shows a lower charge transfer resistance than the others. Lower charge transfer resistance will impact the electrode’s ability on the supercapacitor[54]. The lower charge transfer resis- tance causes a better supercapacitor[55].
3.7. Analysis of GCD
GCD curves at different current densities can be seen inFig. 7.
From the GCD curve, the specific capacitance of the supercapacitor Table 4
Parameter of the specific capacity and open circuit from cyclic potential voltammetry.
Sample Capacitance (F/g) Open circuit potential (V)
AC20/80 37.03 0.56
AC80/20 41.26 0.45
AC40/60 31.85 0.61
AC60/40 25.00 0.48
AC50/50 31.89 0.57
Fig. 6.Nyquist plot magnetic activated carbon.
electrode is obtained. Specific capacities with current density for magnetic activated carbon can be seen inFig. S3. Obtained specific capacitance at AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 at 2 A/g were 142F/g, 150F/g, 136F/g, 121F/g, and 116F/g. Based on the specific capacitance generated from GCD, AC80/20 is the best.
Based on charge transfer resistance (Fig. 6), it is found that AC80/20 has the lowest charge transfer resistance compared to
the others. It causes AC80/20 to have the highest capacitance com- pared to the others based on CV analysis (Fig. 5). Based on GCD analysis, it also has a higher specific capacitance than the others.
Table 5shows the electrochemical performance of different car- bon materials. It was found that AC80/20 has a specific capacitance that is not much different from the others. It shows that activated carbon derived from pecan shell biomass has a promising potential in supercapacitor electrodes.
4. Conclusion
Synthesis of magnetic activated carbon-supported cobalt(II) chloride from biomass with co-precipitation method from pecan shell for the application electrode in supercapacitors has been suc- cessfully carried out. Obtained on the XRD diffractograms show the graphite lattice. Also, a sharp, narrow peak is seen at 2h= 26°in the carbon samples spectrum, showing a highly graphitized fraction.
FESEM-EDX showed AC20/80 that the shape of the particles was like plates indicating that the particles had been formed.
AC80/20 is the surface morphology in which particles with irregu- lar shapes indicate that particles have been formed, where the shape of the particles is irregular, like plates. AC40/60 and Fig. 7. GCD curves at different current densities of (a) AC20/80, (b) AC80/20, (c) AC40/60, (d) AC60/40, and (e) AC50/50. (f) Comparison of specific capacitance with a current density of magnetic activated carbon.
Table 5
The electrochemical performance of different carbon materials.
Electrode Specific Capacitance (F/
g)
Ref
AC/g/Na2SO4@KBr 127 [56]
AC/BSAC 53.49 [57]
KOH activated carbon nano-onion 115 [58]
Porous aerogel composed of carbon onion
157 [59]
VN/MWCNT 160 [60]
Co2P4O12/AC 156 [61]
Acid-treated AC 106 [62]
AC80/20 150 This
study
AC60/40 that the material is not evenly distributed and is still por- ous between particles. AC50/50, the porous carbon surface looks uneven and untidy. In the activation process, these structures and pores are formed. The composition between C and O is also balanced. AC80/20 has lower Co content than AC20/80, AC40/60, AC60/40, and AC50/50 and it appears that AC80/20 is better than the others. The magnitude of the coercivity states that AC20/80, AC80/20, AC40/60, AC60/40, and AC50/50 are strong magnets.
The lower the value of the open circuit potential, it will show elec- trochemical stability. The Nyquist plots of magnetic activated car- bon show a straight vertical indicating the process of charge transfer resistance at the low electrode. Obtained specific capaci- tance AC80/20 at 150F/g. It shows that activated carbon derived from pecan shell biomass has a promising potential in supercapac- itor electrodes.
CRediT authorship contribution statement
Muhammadin Hamid: Supervision, Conceptualization, Methodology, Software.Susilawati:Data curation, Writing – orig- inal draft.Suci Aisyah Amaturrahim:Visualization, Investigation.
Ivi Briliansi Dalimunthe: Software. Amru Daulay: Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing finan- cial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The author would like to thank the Universitas Sumatera Utara for the TALENTA Universitas Sumatera Utara with contract number 2 /UN5.2.3.1/PPM/KP-TALENTA/2022 and Serpong Advanced Char- acterization Laboratory, National Research and Innovation Agency through E-Science Services, National Research and Innovation Agency (BRIN) for scientific and technical support to authors.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.org/10.1016/j.mset.2023.04.004.
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