CO₂-derived hierarchical porous carbon for electrode materials of membraneless electrochemical capacitor

Abstract

Aqueous redox electrochemical capacitors (redox ECs) generally suffer from low energy density and uncontrolled cross diffusion of soluble redox components, causing serious self discharge and capacity fade. This study has designed a membraneless potassium bromide electrochemical capacitor (ML PBEC) single cell generating high energy density with reduced self discharge. From the perspective of CO2 utilization, highly porous carbon with a hierarchical porosity was synthesized from CO2 gas and the change of the electrochemical performance by doping nitrogen on the CO2 derived carbon materials was investigated. Using the synthesized carbon as electrodes with a Br--/Br3 redox active aqueous electrolyte, the designed ML PBEC single cell produced enhanced energy density due to suppressed cross diffusion of soluble bromine molecules through electrostatic interaction between the protons of N doped sites and polybromide anions even without membrane. The designed single cell provided a high energy density equivalent to the highest energy density of membrane contained aqueous electrochemical capacitors, 14.3 Wh kg -1 at 2 A g -1 over 10000 cycles.