Oxophilic Tm‐Sites in MoS₂ Trigger Thermodynamic Spontaneous Water Dissociation for Enhanced Hydrogen Evolution

Abstract 2D MoS₂ is acknowledged as a potential alternative to Pt‐based catalysts for hydrogen evolution reaction (HER) due to its suitable ^*H adsorption energy. However, the weak water adsorption capacity of MoS₂ in an alkaline solution limits its performance improvement toward HER. Herein, a novel rare‐earth Tm single atoms decorated MoS₂ (Tm SAs‐MoS₂) catalyst is proposed, and the key role of Tm SAs on the enhanced HER performance of MoS₂ is identified. It is verified that the Tm‐site in MoS₂ contributes to the asymmetric [Mo‐S‐Tm] unit site, which serves as the electron donor to disturb the electronic state and accelerate electron accumulation at surrounding Mo‐S site. The obtained Tm SAs‐MoS₂ exhibits significantly improved HER activity with a low overpotential of 80 mV at 10 mA cm⁻², robust stability and good selectivity in alkaline solution compared with pure MoS₂ and most MoS₂‐based catalysts. In situ Raman and theoretical calculations prove that the oxophilic Tm in [Mo‐S‐Tm] unit sites significantly improves the migration and thermodynamic spontaneous dissociation of interfacial H₂O molecules during HER by the Tm‐4f‐OH orbital overlap. Such [Tm‐S‐Mo] unit site allows the optimal G_*H location of Tm SAs‐MoS₂, which in turn reaches the apex of the theoretical HER volcano plot. This work is expected to open up new avenues for the design of novel alkaline HER catalysts and provide a valuable understanding of rare earth enhanced mechanisms.