Boosting the electrocatalytic activity of amorphous molybdenum sulfide nanoflakes via nickel sulfide decoration.

As a coordination polymer built of [Mo3S13]2- clusters, amorphous nanoscale MoSx (a-MoSx) is an attractive electrocatalyst for the hydrogen evolution reaction (HER) due to its abundant active sites and scalable synthesis. However, clarifying the internal catalytic mechanism and achieving even higher HER performance with scalable size are still challenging. Herein, a new hybrid catalyst of a-MoSx flakes decorated with Ni3S2 nanocrystals (size < 10 nm) has been successfully synthesized on 10 × 20 cm2-sized Ni foam by a portable hydrothermal route. As the strong interaction of [Mo3S13]2- clusters with Ni3S2 is evidenced by comprehensive binding state and Raman characterization, the polymerization effect of [Mo3S13]2- itself and the perfect interfaces between [Mo3S13]2- clusters and Ni3S2 are also confirmed by density functional theory calculations. These two factors greatly lower the absorption energy of hydrogen nearly to zero, leading to much improved HER activity. Current densities of 100 and 600 mA cm-2 are achieved at overpotentials of 181 and 246 mV, respectively, which are so far the highest values approaching practical applications. The findings of this work provide a fundamental reference about the catalytic origin of a-MoSx based catalysts, and shed light on the practical applications of non-precious electrocatalysts for their compatibility with low cost batch production.