A Self-Supported Porous Hierarchical Core–Shell Nanostructure of Cobalt Oxide for Efficient Oxygen Evolution Reaction

Increasing the active surface area of an electrocatalyst is crucial for effective oxygen evolution reaction (OER). Here, a sophisticated electrode that uses the advantages of porous/hollow nanostructure, hierarchical nanostructure, and self-supported structure simultaneously is demonstrated for the first time. A self-supported porous hierarchical core–shell structure (PHCS) of cobalt oxide is synthesized by the combination of electrochemical deposition and electrochemical treatment. The treatment introduces numerous pores into the core of a core–shell structure, and it decreases the particle size of cobalt oxide to <5 nm, markedly increasing the surface area of the resultant structures. The electrochemical surface area of PHCS is 1.6 greater than that of hierarchical core–shell cobalt oxide, and is ∼20 times greater than that of cobalt oxide nanowires. The PHCS is extremely active in the OER, with the overpotential required for a current density of 100 mA cm –2 being as small as 300 mV. The Tafel slope is 40.3 mV dec –1, and the PHCS can work stably for more than 40 h.