Ultrastable molybdenum disulfide-based electrocatalyst for hydrogen evolution in acidic media

Despite the incredible success in reducing the overpotential of nonprecious catalysts for acidic hydrogen evolution reaction (HER) in the past few years, the stability of most platinum-free electrocatalysts is still poor. Here, we report an ultrastable electrocatalyst for acidic HER based on two-dimensional (2D) molybdenum disulfide (MoS₂) doped with trace amount of palladium (<5 μg cm^-2), which creates sulfur vacancies (S-vacancies). The optimized catalyst shows stable operation over 1000 h at 10 mA cm^-2 with overpotential of 106 mV. The MoS₂ catalyst is stabilized on a defective vertical graphene support, where the strong interaction at the 2D-2D interface increases the adhesion between the catalyst and the support. Palladium (Pd) doping generates rich sulfur vacancies in MoS₂ that have a twofold role: (1) increasing hydrogen adsorption energy, which enhances activity; and (2) further increasing the adhesion between graphene support and defective MoS₂, and thus enhancing stability. Complementary theoretical studies reveal the reaction pathways for substitutional doping, where the Mo-vacancy sites are prior to be doped by Pd. Our work thus offers a strategy for making stable, efficient, and earth-abundant HER catalysts with strong potential to replace platinum for PEM electrolysis.