Pulsed Electrodeposition of Co₃O₄ Nanocrystals on One-Dimensional ZnO Scaffolds for Enhanced Electrochemical Water Oxidation

Pulsed electrodeposition has been introduced to deposit ultrathin flakes of Co₃O₄ nanocrystals on ZnO nanorods. By fixing the seeding process, the scaffolding function of ZnO nanorods was studied by varying deposition times (30 s, 60 s, and 90 s) of Co₃O₄ at a nucleation current of −1.0 mA cm⁻². The amount of deposited Co₃O₄ has a strong influence on the oxygen evolution performance with ZnO scaffolds. To deliver a current density of 10.0 mA cm⁻² in neutral solutions (0.5 M K₂SO₄), the presence of ZnO scaffold electrodes negatively shifted the overpotential by ∼200 mV. In particular, the Co₃O₄/ZnO hybrid nanostructured electrode (60 s) exhibits the lowest onset potential of 1.5 V (vs. reversible hydrogen electrode, RHE). Electrochemical impedance spectra and double layer capacitance showed that the enhanced oxygen evolution activities originated from the improved charge transfer capability and the increased electrochemically active interface between Co₃O₄ and ZnO.