Mesoporous nitrogen, sulfur co-doped carbon dots/CoS hybrid as an efficient electrocatalyst for hydrogen evolution

Hydrogen is an ideal energy carrier for renewable energy, but a high overpotential is required to achieve reasonable H-2 evolution, which makes the design of highly active electrocatalysts for hydrogen evolution reaction (HER) urgent. Here, we report a nitrogen, sulfur co-doped carbon dots (NSCDs)/CoS hybrid with a three-dimensional mesoporous sponge-like nanostructure, fabricated via heat-treatment, which as electrocatalyst exhibits the desired electrocatalytic activity for electrochemical HER. A series of NSCDs/CoS hybrids with different contents of NSCDs were prepared by adjusting the concentration of NSCDs, of which the NSCDs/CoS hybrid with 20 mg L-1 NSCDs exhibits the best electrocatalytic activity towards HER with an onset potential of 0.095 V, an overpotential at 10 mA cm(-2) of 165 mV, a small Tafel slope of 56 mV per decade, and a good stability in 0.5 M H2SO4. The excellent electrocatalytic activity of NSCDs/CoS for HER is attributed to synergetic effects of NSCDs and CoS, in which the NSCDs could protect the CoS from dissolution/agglomeration under acidic conditions, and the increased surface area of the NSCDs/CoS hybrid and the high charge transfer efficiency between NSCDs and CoS via Co-S-C bonding enhanced the HER performance.