Boosting Electrocatalytic Oxygen Evolution: Superhydrophilic/Superaerophobic Hierarchical Nanoneedle/Microflower Arrays of CexCo3-xO4 with Oxygen Vacancies.

The oxygen evolution reaction has become the bottleneck of electrochemical water splitting for its sluggish kinetics. Developing high-efficiency and low-cost non-noble-metal oxide electrocatalysts is crucial but challenging for industrial application. Herein, superhydrophilic/superaerophobic hierarchical nanoneedle/microflower arrays of Ce-substituted Co3O4 (CexCo3-xO4) in situ grown on the nickel foam are successfully constructed. The hierarchical architecture and superhydrophilic/superaerophobic interface can be facilely regulated by controlling the introduction of Ce into Co3O4. The unique feature of hierarchical architecture and superhydrophilic/superaerophobic interface is in favor of electrolyte penetration and bubbles release. In addition, the presence of oxygen vacancy and Ce endows the catalyst with enhanced intrinsic activity. Benefiting from these advantages, the optimized Ce0.12Co2.88O4 catalyst shows a superior electrocatalytic performance for the oxygen evolution reaction (OER) with an overpotential of 282 mV at 20 mA cm-2, and a Tafel slope of 81.4 mV dec-1. The turnover frequency of 0.0279 s-1 for Ce0.12Co2.88O4 is 9.3 times larger than that for Co3O4 at an overpotential of 350 mV. Moreover, the optimized Ce0.12Co2.88O4 catalyst shows a robust long-term stability in alkaline media.