Millisecond synthesis of CoS nanoparticles for highly efficient overall water splitting

High performance and low-cost electrocatalysts for overall water splitting, i.e., catalyzing hydrogen and oxygen evolution reactions with the same material, are of great importance for large-scale, renewable energy conversion processes. Here, we report an ultrafast (~ 7 ms) synthesis technique for transition metal chalcogenide nanoparticles assisted by high temperature treatment. As a proof of concept, we demonstrate that cobalt sulfide (~ 20 nm in diameter)@ few-layer graphene (~ 2 nm in thickness) core-shell nanoparticles embedded in RGO nanosheets exhibit remarkable bifunctional electrocatalytic activity and stability for overall water splitting, which is comparable to commercial 40 wt.% platinum/carbon (Pt/C) electrocatalysts. After 60 h of continuous operation, 10 mA·cm^-2 water splitting current density can still be achieved at a low potential of ~ 1.77 V without any activity decay, which is among the most active for non-noble material based electrocatalysts. The presented study provides prospects in synthesizing highly efficient bifunctional electrocatalysts for large-scale energy conversion application via a simple yet efficient technique.