Achieving high-capacity aqueous supercapacitors via anion-doped construction of dual redox centers in NixCo1−xSeO3

Abstract

In asymmetric supercapacitors, transition metal selenates are promising electrodes, but their capacity are limited by a single redox center. To further enhance the performance of transition metal selenates, Ni_xCo_1−xSeO₃ (NCSeO) doped with N and Cl was prepared on nickel-plated carbon cloth (NCSeO–NCl–NiCC). During electrochemical reactions, NCSeO can be converted to M(OH)₂ (M = Ni/Co) and OH⁻ is replaced by N and Cl. Two redox centers, M(OH)₂/MOOH and M(OH)_xN_2−x/NO₃⁻, are formed during charging and discharging, which is attributed to the increased capacity of the NCSeO–NCl–NiCC electrode. On NCSeO, the substitution of Cl facilitates the regulation of the electronic structure and enhances the stability of N-doping. The optimised electrode exhibits a high capacity of 417 mA h g⁻¹ at 1 A g⁻¹ and an impressive rate capability of 235 mA h g⁻¹ at 50 A g⁻¹. Asymmetric supercapacitors with this design have an ultra-high energy density of 73.6 W h kg⁻¹, as well as an excellent rate and cycling performance with a capacitance retention of 97.8% after 20 000 cycles at a current density of 20 A g⁻¹.