Waste materials as precursors for supercapacitor electrodes

This work highlights the potential to use waste biomass to produce electrodes for cost-effective energy storage systems based on renewable resources. Porous carbon electrodes for supercapacitors were prepared from waste coffee grounds, sugar cane bagasse, pine wood sawdust, and sucrose by activation with ZnCl2. The double-layer capacitances of these carbon electrodes were evaluated in two-electrode supercapacitor cells with 1 M H2SO4. The choice of carbon precursor and activation conditions determine the electrochemical performance, with surface area, pore size distribution, electrical conductivity, and electrochemically active surface functional groups all affecting specific capacitance. The activated carbons from sucrose, pinewood and coffee grounds all exhibited good electrochemical capacitance and stable cycling performance in H2SO4. The activated carbon from coffee grounds achieved the highest specific capacitances at low current loads, with capacitances as high as 368 F g-1 in H2SO4. The good electrochemical performance of the carbons from sucrose, pinewood and coffee grounds is predominantly attributed to well developed pore structures. Although the bagasse carbon has a surface area of 1155 m2 g-1, the bagasse carbons achieved lower specific capacitance and poor stability due to residue silica and ash content