Effect of structural and compositional alterations on the specific capacitance of hazelnut shell activated carbon

Abstract Hazelnut shell activated carbon materials (HSACs) are promising electrode materials used for supercapacitors, due to their superior natural performance. In this research, characterizations of surface features and electrochemical performance on a series of HSACs prepared with changing calcination temperature and mass ratio of activators showed that HSACs with larger specific surface area experienced lower specific capacitance. Further structural and compositional evaluations of the HSACs by Raman and X-ray photoelectron spectroscopy revealed that upon increasing calcination temperature or activator content, the specific surface area increased, but the carbon sp2/sp3 ratio and the concentration of acidic surface oxide groups decreased, and the population of basic surface oxide groups increased. These latter trends might be responsible for the decrease of specific capacitance of HSACs. The more Zn(NO3)2 activator was suppressed, the more basic surface oxide groups generated. In conclusion, this study clarified that the capacitance performance of HSACs was affected by the combined effect of micropore features and structural characteristics of HSACs, including electrical conductivity of sp2 C˭C bonds, various functional groups content, and groups inducing changes in adsorption property.