Boosting highly active defect Mo^V sites for amorphous molybdenum sulfide from catalyst-substrate effect toward efficient hydrogen evolution

Simultaneously achieving abundant active sites and high intrinsic activity is a major challenge to developing highly efficient MoS_x-based materials for hydrogen evolution reaction (HER) since there might be a contradictory relationship between loading amounts and intrinsic activity of amorphous molybdenum sulfide (MoS_x). Herein, we have for the first time demonstrated a strategy for the electrochemical oxidation of carbon cloth (CC) followed by mild acidification employing (NH₄)₂MoS₄ as the precursor to boost highly active defect Mo^V sites (DMSs) for MoS_x toward efficient HER. In our strategy, a high potential at the anode results in a high concentration of O-containing groups on the surface of CC, which favors loading [Mo₃S₁₃]²⁻ clusters or MoS_x on CC (MoS_x/CC) for achieving abundant DMSs. Impressively, such oxidation does not disrupt the sp² hybridized carbon of the substrate. Hence, the excellent conductivity of CC guarantees high intrinsic activity of the as-synthesized MoS_x/CC samples. On the other hand, excessively high potential stimulates excessive growth and accumulation of [Mo₃S₁₃]²⁻ clusters for further increasing loading amounts of MoS_x. Nevertheless, such loading is at the expense of DMSs, indicating a great decrease in the quantity of active sites. Furthermore, excessive oxidation leads to unsatisfactory conductivity of CC, owing to breaking the sp²-conjugated system of CC. At the same time, the theoretical prediction and experimental investigation reveal that the intrinsic activity of DMSs will significantly decrease at excessively high potential. By regulating electrochemical potential to 1.8 V, a balance between the loading amounts of MoS_x and intrinsic activity of MoS_x/CC is achieved to boost highly active DMSs for efficient HER. Consequently, the optimal MoS_x/CC exhibit the most excellent HER activity among all counterparts, accompanied by reliable stability. This work presents a new strategy for realizing abundant active sites with high intrinsic activity for MoS_x-based materials toward efficient HER from the catalyst-substrate effect.