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

Abstract

As a coordination polymer built of [Mo₃S₁₃]²⁻ clusters, amorphous nanoscale MoS_x (a-MoS_x) 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-MoS_x 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-MoS_x based catalysts, and shed light on the practical applications of non-precious electrocatalysts for their compatibility with low cost batch production.