Computational screening of M₁/PW₁₂O₄₀ single-atom electrocatalysts for water splitting and oxygen reduction reactions

A cost-effective and highly-efficient electrocatalyst with excellent catalytic activity and stability is essential for practical applications in water splitting, including oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). Single-atom catalysts (SACs) have provided the opportunity for revolutionizing industrial catalysis owing to their remarkable advantages, such as efficient atom utilization, strong metal-support interactions, unsaturated coordination configurations, single active sites, and the potential to achieve high catalytic performance and selectivity. In this study, we have applied spin-polarized density functional theory (DFT) to systematically investigate the electrocatalytic performance of transition metal-phosphotungstic acid (M₁/PTA) clusters-based SACs for HER, OER, and ORR. The theoretical analysis revealed that the single metal adatoms (SMAs) bind most favorably to the fourfold hollow (4H) sites on the PTA cluster, which exhibits higher stability and catalytic activity, allowing fast electron transfer kinetics through catalysis. The Volmer-Heyrovsky pathway results in nearly optimal ΔG_H* values (ΔG_H* = 0), leading to decent catalytic performance towards the HER for M₁/PTA (M = Ru, Pt, Ti, V, and Rh). Metals such as Co₁/PTA (0.39 V) and Pt₁/PTA (0.47 V) demonstrate comparable overpotentials to phosphomolybdic acid (Co₁/PMA), MoC₂, IrO₂, and RuO₂, making them active and selective OER catalysts. A non-noble metal Co₁/PTA, with an overpotential of 0.52 V, was found to be a promising electrocatalyst for ORR, with an overpotential close to the most favorable Fe₁/PMA (0.42 V) catalyst among the best candidates. Pt₁/PTA shows potential as a multifunctional electrocatalyst for overall water splitting (−0.08 V for HER and 0.47 V for OER) and metal-air battery (0.55 V for ORR) catalysts. To provide an understanding of the superior catalytic performance of Co₁ and Pt₁ SACs in OER and ORR, we further explored the kinetic potential energy barrier. The findings demonstrate that the kinetic activation barrier estimation for all PCET steps corresponds well to the thermodynamic results. In addition, the bonding interactions between M₁/PTA and H₂O or O₂ molecules were analyzed using frontier molecular orbitals and radial distribution function (RDF). This study revealed that the PTA cluster has low-cost and highly efficient electrocatalytic activity under ambient reaction conditions, making it a promising single-atom support for the HER, OER, and ORR.