Electrodeposited Heterostructures of Cobalt Sulfide/Molybdenum Sulfide Trigger both Acidic and Alkaline HER

MoS 2 has attracted significant attention as a non-platinum group electrocatalyst for the hydrogen evolution reaction (HER). There have been extensive efforts demonstrating that by doping MoS 2 with various transition metals, such as Co, the HER activity of the catalyst is enhanced. In particular, this work has shown that various cobalt sulfide phases can act as a co-catalyst with MoS 2 . Here, we report on the electrodeposition of a c-CoS x /MoS 2 heterostructure catalyst for the HER reaction in both acidic and alkaline conditions. Using Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and scanning electron microscopy, it is demonstrated that depending on the precursor concentrations, various morphologies, grain size, and c-CoS x phases can be achieved, all of which have an impact on the activity and stability of the c-CoS x /MoS 2 catalysts. The most promising catalyst composition demonstrated excellent stability in both acidic and alkaline conditions with low overpotentials to reach 10 mA cm −2 of 112 mV and 60 mV and with Tafel slopes of 113 mV dec −1 and 81 mV dec −1 , respectively. This report demonstrates that the c-CoS x /MoS 2 heterostructure is one of the most catalytically active materials for HER, especially in alkaline conditions.