Bi-Directional Electrolytic Reduction of CO₂ to Mesoporous Carbons with Regulated Structure and Surface Functional Groups for Zn-ion Capacitors

Zn-ion capacitors (ZICs) take advantage of batteries and supercapacitors in delivering high energy and power densities for energy storage by using porous carbons due to their low cost, lightweight, high conductivity, and good stability. However, it remains a grand challenge to regulate the mesoporous structures of carbons, including pore sizes and surface functional groups, which are essential for ion transport and electrochemical reactions of ZICs. Herein, a bi-directional electrolysis strategy is developed to directly reduce CO2 to oxygen-rich mesoporous carbons (OMCs) with adjustable pore sizes and oxygen-bearing functional groups, which are preferred for ZICs as theoretically proved by density functional theory (DFT). The designed OMCs exhibit a remarkable energy density of 216.6 Wh kg(-1) and performance retention of 90% after 15000 cycles. When assembled in the flexible ZICs, the OMCs demonstrate a high capacitance of 329.5 mAh g(-1). This work presents a novel strategy for synthesizing OMCs through a decarbonization process and reveals the crucial role of microstructure and surface functional groups in promoting the performance of ZICs.