Engineering RuO2 on CuCo2O4/CuO nanoneedles as multifunctional electrodes for the hybrid supercapacitors and water oxidation catalysis

Currently, designing and constructing multifunctional electrodes is highly desirable for energy conversion and storage devices. Spinel cobaltites have attracted considerable attention owing to the relative high conductivity and rich redox chemistry, but the limited electroactive sites and poor surface chemical reactivity are the highly concerned issues. Taking Co-Cu oxides as the model material, here we demonstrate that a surface restructuring strategy by constructing core-shell arrays can achieve simultaneous modulation of electroactive sites and surface chemical reactivity. Strating from the hydrothermal and annealing process, CuCo2O4/CuO nanoneedles are synthesized directly on the conductive Ni foam, and followed by electrodeposited RuO2 nanoparticles (denoted as CuCo2O4/CuO@RuO2). Core-shell CuCo2O4/CuO@RuO2 arrays show a high areal capacity up to 862.5 mAh cm(-2) and a high capacity retention of about 90.1% after 8000 cycles. Moreover, the hybrid supercapacitor by CuCo2O4/CuO@RuO2 and activated carbon can achieve 0.84 mWh cm(-2) energy density at 8 mW cm(-2) power density, as well as good long-term stability. In addtion, working as water oxidation catalysis, CuCo2O4/CuO@RuO2 shows the low overpotential of 279 mV at 10 mA cm(-2), as well as a low Tafel slope and stable long-term performance. This work provides a novel strategy to engineer surface nanostructure for energy conversion and storage devices. (C) 2020 Elsevier B.V. All rights reserved.