Spherical Sacrificial ZnO Template–Derived Hybrid Ni/Co3O4 Cubes as Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Heterostructure transition metal derivatives have been extensively studied in electrocatalysis, but most of the hybrid samples are on nanoscale with low stability and tap density. ZnO microspheres are applied as a sacrificial template, followed by alkaline etching and aluminum reduction to construct Ni/Co 3 O 4 microcubes. The porous hybrid microcubes show stirring performance in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). For HER, it exhibits comparable overpotential of 145 mV at 10 mA cm −2 as Pt/C (101 mV) and desirable stability. For OER, it outperforms RuO 2 with lower overpotential when the current exceeds 17.8 mA cm −2 and much smaller Tafel slope of 34 mV dec −1 versus RuO 2 (72 mV dec −1 ). The potential activity is assigned to the charge transfer at the heterointerfaces, and the synergic effects of the Ni/Co 3 O 4 phases, which possibly will cast light on the design of microscale bifunctional electrocatalysts.