Vacancy Engineering of Selenium-Vacant NiCo₂Se₄ with Enhanced Electrochemical Performance for Supercapacitor

Vacancy engineering effectively modulates the electronic properties of electrode materials, thereby improving their electrochemical performance. In this study, we prepared selenium-deficient NiCo₂Se₄ (Se_v-NCS) using ethylene glycol as a reducing agent in NaOH alkaline environment, and investigated its potential as an electrode material for supercapacitors. Both theoretical and experimental results confirmed that the introduction of vacancies altered the morphology and electronic structure of NiCo₂Se₄, which in turn synergistically improved the conductivity and the diffusion capability of electrolyte ions. The optimized Se_v-NCS electrode achieved an excellent specific capacitance of 2962.7 F g^-1 at a current density of 1 A g^-1 and superior cycling stability with a capacitance retention of 89.5% even after 10,000 cycles. Furthermore, an asymmetric device composed of the optimized Se_v-NCS electrode as the positive electrode and activated carbon as the negative electrode achieved an energy density of 55.6 Wh kg^-1 at a power density of 800 W kg^-1. Therefore, this work offers novel insights into the role of vacancy engineering in improving the performance of transition metal compound-based electrode materials for supercapacitor.