Theoretical Investigation of Hydrogen Production from Alkaline Media Through TiO2-Supported Triple-Atom Catalysts

Developing low-cost, non-noble-metal electrocatalysts to replace platinum-based benchmarks for the alkaline hydrogen evolution reaction (HER) remains a critical challenge. Using density functional theory (DFT) calculations combined with the computational hydrogen electrode (CHE) model, we systematically investigate the thermodynamics, kinetics, and intrinsic reaction mechanism of HER on a TiO2-supported Ni3 trimer (Ni3/TiO2) in alkaline media. We find that the Ni3 trimer, rather than the TiO2 support, provides multiple active sites for intermediate adsorption. The trimeric Ni3 motif generates delocalized electronic states, leading to electron-rich active sites that significantly lower the barrier for water dissociation, facilitate intermediate desorption, and sustain catalytic turnover. The reaction proceeds predominantly via the Volmer–Heyrovsky pathway, where either water dissociation or H2 desorption can be the rate-determining step, depending on the applied potential. Crucially, the significantly reduced reaction barrier heights demonstrate that the alkaline HER activity of Ni3/TiO2 is comparable to that of benchmark Pt1/TiO2 single-atom catalysts (SACs). This work establishes a promising design strategy for constructing high-performance non-noble metal few-atom catalysts (FACs) to replace noble metal SACs for multi-step electrocatalytic reactions.