Synthesis of activated carbon monolith derived from cocoa pods for supercapacitor electrodes application

ABSTRACT

Agricultural and agro-industrial residues are ordinary wastes in the forestry industry and their valorization is an important issue.Cocoa (Theobroma cacao) pods waste was chosen as an activated activated carbon material and studied as active materials for supercapacitor electrodes. The carbon electrode has been made using 0.3 M and 0.4 M Potassium Hydroxide (KOH) activators at 700°C. Physical properties were tested by measuring density, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), while the electrochemical properties were tested using the Cyclic Voltammetry (CV) method. Activated carbon electrodes were constructed by a combination of chemical activation, and physical activation methods. The technique of making carbon electrodes was started from pre-carbonization, milling, chemical activation, pellet making, carbonization, and physical activation. Analysis of dimensions, density, and specific capacitance in the manufacture of carbon electrodes showed the mass, diameter, thickness, and density of the electrodes decreased with the addition of KOH concentrations from 0.3 M to 0.4 M. While the specific capacitance value of the electrode was directly proportional to the increase of KOH concentration. In XRD measurement data, the values of 2θ in the range of 23.569°–24.747° was obtained for the reflection field 002, and 44.634°–44.781° for the reflection plane 100. X-ray diffraction curve data showed a 0.4 M at 700°C sample having an L_c value and a lattice distance smaller than the sample of 0.3 M at 700°C. Therefore, it could be indicated that the surface area of the sample of 0.4 M at 700°C was greater than the sample of 0.3 M at 700°C. The electrochemical test showed that the method of chemical activation variation of 0.4 M produced electrodes with better performance than 0.3 M. The specific capacitance value obtained at a concentration of 0.3 M was 90.2 F/gr with a density of 0.850 gr/cm³, while at a concentration of 0.4 M was 140.2 F/gr with a density of 0.802 gr/cm³. These results indicate the high potential of agricultural cocoa pods based activated carbon monoliths as supercapacitor electrode.

KEYWORDS:

• Cocoa
• activated carbon
• electrodes
• supercapacitors
• physical properties

Acknowledgments

An appreciation goes to Ministry of Education, Republic of Indonesia for the research funding provided through the Hibah Penelitian Dasar (Basic Research Grant) with contract Number: 042/PL9.1.4/PP/2019.