High capacitance performance of hierarchically SiO2 self-doped porous activated carbon derived from palm empty fruit bunches

Abstract

Porous activated carbon derived from empty fruit bunch (EFB) has garnered significant attention as an electrode material for supercapacitors due to its low cost, abundance, and sustainability in real energy storage applications. However, there is still room for improvement in their performance compared to other renewable biomass resources. In our study, we successfully converted EFB biomass into porous activated carbon with outstanding performance, achieving a remarkably high specific capacitance of 459.28 F/g at 0.5 A/g, along with a moderate specific surface area (SSA) of 1215.38 m2/g. Furthermore, the quasi-solid-state supercapacitor assembled from the AC700 sample demonstrated excellent energy density, reaching 15.39 Wh/kg at a power density of 50 W/kg. Additionally, it exhibited remarkable cycling stability, with a capacitance retention of 93 % after 10,000 cycles. These exceptional results were achieved by simply adjusting the activation temperature. We utilized KOH as the activating agent and carbonized it at temperatures of 600 °C, 700 °C, and 800 °C for 2 h under an N2 atmosphere. The superior capacitive performance of the AC700 sample can be attributed to the combined effects of its high SSA, surface functional groups, and optimal pore size distribution. The optimum activation temperature of 700 °C resulted in the formation of porous activated carbon with the most structural defects, as well as an appropriate distribution of micropores (63.41 %) and mesopores (31.70 %), facilitating ion diffusion and providing multiple sites for charge storage. Additionally, the AC700 sample exhibited the highest SiO2 content, measuring at 34.33 %, and the lowest contact angle of 75°. The presence of SiO2 in the carbon framework promotes the formation of more hydrophilic active sites, thereby enhancing the pseudocapacitance performance and facilitating sufficient wetting between the electrolyte and electrode interface.