Hierarchical hollow urchin-like NiCo2O4 nanomaterial as electrocatalyst for oxygen evolution reaction in alkaline medium

Hierarchical hollow urchins of NiCo2O4 (HU-NiCo2O4) were synthesized by a hard templating method followed by thermal decomposition. The structure consists of three levels of hierarchy i.e., zero-dimensional nanoparticle with a diameter of about 6 nm, one-dimensional chain, and three-dimensional hollow urchin, respectively. Nanoparticle aggregates of NiCo2O4 (NA-NiCo2O4) were also synthesized by the same procedure in the absence of the hard template. Relative to NA-NiCo2O4, HU-NiCo2O4 features a well-connected three-dimensional porous structure, which is beneficial for diffusion of oxygen.. Consequently, HU-NiCo2O4 displayed superior electrocatalytic activity towards oxygen evolution processes with lower overpotential, higher current density, and higher stability than NA-NiCo2O4. (C) 2014 Elsevier B.V. All rights reserved.