Structure evolution of oxygen removal from porous carbon for optimizing supercapacitor performance

Abstract

The presence of oxygen functional groups is detrimental to the capacitive performance of porous carbon electrode in organic electrolyte. In this regards, hydrogen thermal reduction has been demonstrated effective approach in removing the unstable surface oxygen while maintaining the high porosity of carbon matrix. However, the exact evolution mechanism of various oxygen species during this process, as well as the correlation with electrochemical properties, is still under development. Herein, biomass-based porous carbon is adopted as the model material to trace its structure evolution of oxygen removal under hydrogen thermal reduction process with the temperature range of 400–800 °C. The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700°C. XPS, TPR-MS and Boehm titration results indicate that the oxygen elimination undergoes three distinctive stages (intermolecular dehydration, hydrogenation and decomposition reactions). The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700 °C. Benefiting from the stable electrochemical interface and the optimized porous structure, the as-obtained HAC-700 exhibit significantly suppressed self-discharge and leak current, with improved cycling stability, which is attributable to the stabilization of electrochemical interface between carbon surface and electrolyte. The result provides insights for rational design of surface chemistry for high-performance carbon electrode towards advanced energy storage.