Transition Metal Single-Atom-Anchored PdN2 Monolayer for Superior Alkaline Hydrogen Oxidation Reactions

The sluggish kinetics of alkaline hydrogen oxidation reaction (HOR) and high cost of Pt–based catalysts have long hindered large–scale deployment of alkaline membrane fuel cells. Via first–principles calculations, we designed a series of 3d transition metal single atoms anchored on PdN2 monolayer (TM–PdN2, TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and evaluated their alkaline HOR performance. Ti-, Cr-, Fe-, Co-, Ni-modified systems exhibit excellent thermodynamic and electrochemical stability under operating conditions. Single-atom doping tunes the p-band center of N and d-band center of metal sites, enabling precise modulation of H and OH adsorption strengths. Mechanistic analysis reveals HOR follows H2 + 2OH* → H* + OH* + H2O → 2H2O, with the final step as rate-determining step. H adsorption contributes 3.45 times more to HOR activity than OH adsorption. Fe–PdN2 delivers the best performance, with an ultra–low barrier of 0.11 eV and a rate constant of 2.82 × 1010 s–1·site−1, values that significantly outperform those of Pt(111) (0.22 eV, 4.5 × 109 s−1·site−1). This work provides theoretical guidance for rational design of high–performance alkaline HOR electrocatalysts.