S, N co-doped carbon nanotube-encapsulated core-shelled CoS2@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/CoS2@Co) serving as a bifunctional catalyst, which exhibits excellent hydrogen evolution reaction performance (10.0 mA cm-2 at 0.112 V, and low Tafel slope for 104.9 mV dec-1) and oxygen evolution reaction performance (10.0 mA cm-2 at 1.57 V, and low Tafel slope for 76.1 mV dec-1), 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-2 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.