Polyoxometalate-based single-atom catalysts (POM–SACs) offer precise control over the structural and electronic environment of anchored transition metals (TMs) and their supports. In this study, we explored the catalytic performance of TMs anchored on a Lindqvist-type hexavanadate cluster, [(V₆O₁₉)]8−, forming TM@POV catalysts for the hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR) reactions. Using density functional theory (DFT), we evaluated their thermodynamic, structural, and thermal stability at the most favorable three-hollow (3H) sites of the POV framework. The complete HER mechanism was investigated via the Volmer, Volmer–Heyrovsky, and Volmer–Tafel pathways. The lowest HER overpotentials were observed for Sc@POV (ΔGH⁎ = −0.03 eV) and Ni@POV (ΔGH⁎ = 0.03 eV) through the Volmer–Tafel pathway. Electronic descriptors including the d-band center (εd), Bader charge (q/e), projected density of states (PDOS), and charge density difference (CDD) revealed efficient charge redistribution between metal centers and hydrogenated/oxygenated intermediates. For OER, Co@POV exhibited the lowest overpotential (ηOER = 0.43 V) at the second step (OH⁎ → O⁎), while Ni@POV achieved the best ORR performance (ηORR = 0.65 V) at the final step (OH⁎ → H₂O). Incorporating solvation effects through the VASPsol model further enhanced catalytic activity. The explicit solvation model with one water molecule achieved the lowest overpotentials (ηOER/ηORR = 0.32/0.44 V), demonstrating improved charge transfer and proton coupling. Overall, these findings provide fundamental insights into designing low-cost, thermally stable, and highly efficient TM@POV-based multifunctional electrocatalysts for hydrogen production (H2) and sustainable energy conversion.
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