Rational Design of Co(II) Dominant and Oxygen Vacancy Defective CuCo₂O₄@CQDs Hollow Spheres for Enhanced Overall Water Splitting and Supercapacitor Performance

Abstract

The hierarchical CuCo₂O₄@carbon quantum dots (CQDs) hollow microspheres constructed by 1D porous nanowires have been successfully prepared through a simple CQDs-induced hydrothermal self-assembly technique. XPS analysis shows the CuCo₂O₄@CQDs possesses the Co(II)-rich surface associated with the oxygen vacancies, which can effectively boost the Faradaic reactions and oxygen evolution reaction (OER) activity. For example, the as-synthesized 3D porous CuCo₂O₄@CQDs electrode exhibits high activity toward overall electrochemical water splitting, for example, an overpotential of 290 mV for OER and 331 mV for hydrogen evolution reaction (HER) in alkaline media have been achieved at 10 mA cm^-2, respectively. Furthermore, an asymmetric supercapacitor (ASC) (CuCo₂O₄@CQDs//CNTs) delivers a high energy density of 45.9 Wh kg^-1 at 763.4 W kg^-1, as well as good cycling ability. The synergy of Co(II)-rich surface, oxygen vacancies, and well-defined 3D hollow structures facilitates the subsequent surface electrochemical reactions. This work presents a facile method to fabricate energetic nanocomposites with highly reactive, durable, and universal functionalities.