Tandem Ru-Tm Sites on MoS₂ Tune Entropy-Enthalpy Tradeoff for Enhanced Alkaline Hydrogen Evolution

Rare earth (RE) regulation has emerged as an effective strategy for improving hydrogen evolution reaction (HER), but RE kinetic behaviors are widely discussed from an adsorption energy perspective, with neglectful apparent activation energy (E_a) and entropy (Δ^‡S) contributions. This work develops an effective tandem catalyst of Ru anchored on MoS₂ decorated with Tm single-atom sites (Ru/Tm SAs-MoS₂), and reveals a tandem Ru-Tm site-derived entropy-enthalpy tradeoff in alkaline HER. The Ru/Tm SAs-MoS₂ delivers a low overpotential of 8 mV at 10 mA cm^-2 toward HER and achieves 1.0 A cm^-2 at only 1.74 V with excellent operating life over 600 h in anion-exchange membrane water electrolysis. Temperature-dependent kinetic analysis reveals that Tm incorporation reshapes the HER kinetic origin through a potential-dependent entropy-enthalpy tradeoff mechanism. At low overpotentials, Tm reduces E_a to improve reaction activation; At elevated overpotentials, the amplified Δ^‡S contribution offsets the elevated energy barrier of HER. In situ and theoretical characterizations verify that Tm incorporation not only reorganizes an interfacial hydrogen-bond network to underpin Δ^‡S-correlated kinetic behavior, but also tunes the electronic structure of Ru and mitigates overabundant electronic reconstruction upon H* adsorption. This work provides a new insight into understanding the role of RE in regulating alkaline HER kinetics.