Identification of pH-dependent synergy on Ru/MoS₂ interface: a comparison of alkaline and acidic hydrogen evolution

Engineering bifunctional interfaces for enhanced alkaline hydrogen evolution reaction (HER) kinetics is achieved by rational coupling of Ru nanoparticles and defect-rich MoS₂ nanosheets via a simple wet-chemical method. Comprehensive material characterizations, especially high-resolution transmission electron microscopy, reveal well-defined interfaces between both components, leading to interfacial synergy whereby Ru expedites water dissociation and nearby defect-rich MoS₂ enables favorable hydrogen adsorption for recombination into H₂. The designed Ru/MoS₂ material demonstrates remarkable catalytic activity towards alkaline HER (-13 mV at -10 mA cm^-2) with stable operation after 12 h or 1000 cycles, which is superior to almost all Ru-based and MoS₂-based electrocatalysts and even outperforms commercial 20 wt% Pt/C at overpotentials larger than -78 mV in alkaline media. No improved HER activity is observed for Ru/MoS₂ in acidic electrolyte (-96 mV at -10 mA cm^-2), which is even inferior to Ru/CP (-78 mV at -10 mA cm^-2). The correlation between alkaline and acidic HER results confirms that the intrinsic HER activity of this material originates from the desired synergistic effect under alkaline conditions.