NiCo2S4 sub-micron spheres: an efficient non-precious metal bifunctional electrocatalyst.

Urchin-like NiCo2S4 sub-micron spheres integrated with nano-sized and micro-sized structures, which were synthesized via a facile one-pot method, deliver efficient electrocatalytic activities for oxygen reduction and evolution reactions. The excellent electrocatalytic property of NiCo2S4 sub-micron spheres is originated from their unique urchin-like microstructure, composition and d-electronic configurations of the transition metal ions.