BIOMASS-DERIVED HIERARCHICAL POROUS CARBON DECORATED WITH ZNO NANOPARTICLES FOR ENHANCED ELECTROCHEMICAL ENERGY STORAGE

Abstract

The research aimed at the development of sustainable and highly-efficient electrodes is very important for increasing the storage of energy in supercapacitors. The hierarchical porous carbon (HPC), obtained from the biomass, serves as a cheap and porous conductor; however, the efficiency of the HPC as a material for storing energy might be insufficient due to the lack of pseudocapacitance activity. The same concerns the zinc oxide (ZnO), which possesses electrochemically active sites but has a low electrical conductivity. Thus, the combination of these two materials seems very promising; however, the effect of ZnO loading amount on the structure and electrochemical characteristics of the HPC, obtained from the rice husk, has not been sufficiently studied yet. In this paper, the HPC was synthesized from the rice husk using carbonization and KOH activation, and then ZnO nanoparticles were doped into the structure. Composites of HPC/ZnO with the mass ratios of 5%, 15%, and 20% ZnO were prepared and characterized. The electrochemical characterization was done by different methodologies such as cyclic voltammetry, galvanostatic charge-discharge analysis, electrochemical impedance spectroscopy, rate capability, cycling stability, and charge storage kinetics. HPC/ZnO-15 showed the highest specific capacitance of 380 F g⁻¹ among all the synthesized samples while the pristine HPC had the specific capacitance of 250 F g⁻¹ at the current density of 1 A g⁻¹. Moreover, the optimized composite maintained 75% capacitance at the current density of 10 A g⁻¹. An asymmetric supercapacitor prepared from the optimized composite was also evaluated for the potential applications in energy storage system.