Catalytic Hydrogen Evolution Reaction Enhancement on Vertically Aligned MoS₂ by Synergistic Addition of Silver and Palladium

Hybrid electrodes containing MoS₂ with metals active for the hydrogen evolution reaction (HER) are highly desirable as they can provide a cost-effective and active route for producing hydrogen. It is well known that the technique used to facilitate such hybrid formation plays a critical role in the activity and stability of the electrode. Here we utilized a novel method for hybridization based on electron-beam deposition of Ag, Pd, and Mo to make precursor films which, upon sulfurization, formed hybrid electrodes based on vertically aligned molybdenum disulfide (VA-MoS₂). We further modified the surface of these electrodes by exploiting galvanic replacement of palladium. Surprisingly, both hybridization techniques showed a synergistic effect between Pd and Ag, and enhanced activity was enabled by the presence of both metals. XPS, XRD, Raman spectroscopy, and FIB-EM were used to explore the root cause of the synergy. It appears that enhanced performance is based partially on the mutual solubility of Pd−Ag and the facile diffusion of Ag through the MoS₂ film. Ag/VA-MoS₂ modified by galvanic replacement provided 10 mA/cm² at 210 mV of overpotential and was stable for up to 4000 cycles, surpassing the stability of previously reported Pd/MoS₂ hybrids, making these techniques of interest for future generations of hybrid HER electrodes based on MoS₂.