Correlation studies between pore structure and electrochemical performance of activated polymer-based hard carbon with various organic and aqueous electrolytes

Summary In this study, activated polymer-based hard carbon (APHC) was first prepared using CO2 activation. Then electrochemical measurements of APHC-applied electrodes were used to evaluate these electrodes for application to electric double-layer capacitors. The APHCs were prepared under different conditions of activation temperature and time. The APHCs that were activated at 1000°C for 40 and 50 minutes showed good textural properties (specific surface area: 2440 and 2210 m2/g, mesopore fraction: 43.5% and 63.1%, respectively). These properties were observed using the N2/77 K adsorption isotherm, and APHCs have favorable pore structures for ion adsorption in electrolytes. Electrochemical techniques such as galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopy were used to assess the capacitive behaviors and rate performance of the APHCs in various electrolytes. The specific capacitance of the APHCs showed different results depending on the electrolytes used. APHC-10-50 showed 117 F/g of specific capacitance in propylene carbonate (PC), but only 106 F/g in acetonitrile (AcN), very different from APHC-10-40 (77 F/g in PC and 120 F/g in AcN). Although APHC-10-50 had a smaller specific surface area than that of APHC-10-40, it exhibited a high mesopore fraction with pore size optimal for PC electrolyte, which has larger ions and clusters than AcN does. This can lead to a relatively higher specific capacitance of APHC-10-50 in PC electrolyte than that of APHC-10-40 due to the high mesopore fraction.