Enhancing Interfacial Capacitance by Boron Doping in Vertically Porous Carbon Toward High‐Performance AC Filtering Electrochemical Capacitors

Abstract Electrochemical capacitors (ECs) show great perspective in alternate current (AC) filtering once they simultaneously reach ultra‐fast response and high capacitance density. Nevertheless, the structure‐design criteria of the two key properties are often mutually incompatible in electrode construction. Herein, it is proposed that combining vertically oriented porous carbon with enhanced interfacial capacitance (C_i) can efficiently solve this issue. Theoretically, the density function theory calculation shows that the C_i of a carbon electrode can be enhanced by boron doping due to the corresponding compact induced charge layer. Experimentally, the vertical‐oriented boron‐doped graphene nanowalls (BGNWs) electrodes, whose C_i is enhanced from 4.20 to 10.16 µF cm⁻² upon boron doping, are prepared on a large scale (480 cm²) using a hot‐filament chemical vapor deposition technique (HFCVD). Owing to the high C_i and vertically oriented porous structure, BGNWs‐based EC has a high capacitance density of 996 µF cm⁻² with a phase angle of − 79.4° at 120 Hz in aqueous electrolyte and a high energy density of 1953 µFV² cm⁻² in organic electrolyte. As a result, the EC is capable of smoothing 120 Hz ripples for 60 Hz AC filtering. These results provide enlightening insights on designing high‐performance ECs for high‐frequency applications.