Ag₂S/MoS₂ Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution...

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag₂S, MoS₂, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS₂ nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS₂ and MoS₂/RGO, the Ag₂S/MoS₂ anchored on the RGO surface (the ternary system Ag₂S/MoS₂/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (-190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of -10 mA/cm² and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag₂S/MoS₂/RGO ternary catalyst at an overpotential of -200 mV demonstrated a turnover frequency equal to 0.38 s^-1. Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge-transfer resistance (98 Ω) at -155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS₂ and Ag₂S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.