S, N co-doped carbon nanotube-encapsulated core-shelled CoS@Co nanoparticles: efficient and stable bifunctional catalysts for overall water splitting.

Hydrogen, serving as a clean, sustainable energy source, may be mainly produced from electrolysis water. Herein, we report cobalt disulphide encapsulated in self-catalyzed carbon nanotubes (S, N-CNTs/CoS@Co) serving as a bifunctional catalyst, which exhibits excellent hydrogen evolution reaction performance (10.0 mA cm at 0.112 V, and low Tafel slope for 104.9 mV dec) and oxygen evolution reaction performance (10.0 mA cm at 1.57 V, and low Tafel slope for 76.1 mV dec), meanwhile with a strong stability at various current densities. In-depth study reveals that the excellent catalytic properties can be mainly attributed to the increased catalytic sites induced by S, N co-doping, the improved electronic conductivity derived from the carbon nanotubes, and Mott-Schottky effect between the metal cobalt and semiconductive cobalt disulfide. Notably, when the bifunctional catalysts are applied to overall water splitting, a low potential of 1.633 V at the current density of 10.0 mA cm is achieved, which can compete with the precious metal catalyst benchmarks in alkaline media, demonstrating its promising practicability in the realistic water splitting application. This work elucidates a practicable way to the design of transition metal and nano-carbon composite catalysts for a broad application in the fields of energy chemistry.