Se vacancy-driven nickel cobalt selenide electrode enhancing reaction kinetics for boosting supercapacitive performance

Abstract

Nickel cobalt selenide presents a typical Faraday charge storage mechanism, but its electrochemical performance is limited due to its poor reaction kinetics. As a common defect type, vacancy defects can eliminate the limitations of intrinsic chemical and structural characteristics, thereby improving the reaction kinetics of the electrode. Herein, we report a V_a-NiCo₂Se_x nanomaterial with adjustable Se vacancy concentrations achieved by NaBH₄ induction, realizing an enhancement of the performance of the supercapacitor. This adjustment of vacancy concentrations can not only essentially regulate the adsorption site and ion valence state and enhance the adsorption capacity and redox activity of ions, but also reveal the significant improvement of vacancy modification on the surface reaction kinetics of electrode materials through density functional theory (DFT) calculation. The electrochemical results show that the V₂-NiCo₂Se_x electrode material with optimal vacancy concentrations has the highest specific capacity of 310.8 mA h g⁻¹ at 1 A g⁻¹. The assembled hybrid supercapacitor V₂-NiCo₂Se_x//AC-HSC can provide a high energy density of 76.5 W h kg⁻¹ at a power density of 800.1 W kg⁻¹. This work provides an effective strategy for exploring the structure–function relationship between vacancy concentrations and electrochemical performance.