Hierarchical Porous P-Doped NiCo Alloy with α/ε Phase-Defect Synergy to Boost Alkaline HER Kinetics and Bifunctional Activity

Non-precious catalysts for alkaline hydrogen evolution reaction (HER) face a fundamental multi-scale challenge: lack of synergy between electronic structure tuning for balancing H adsorption and water dissociation, active site stabilization for boosting intrinsic turnover frequency (TOF), and mass transport. Even Pt loses 2-3 orders of magnitude activity in alkaline media due to inefficient water dissociation, a synergistic gap unresolved by the Sabatier principle alone. Existing strategies only address isolated aspects: phase engineering optimizes electronic structure but not active site stability; heteroatom doping introduces defects unlinked to mass transport; and nanostructuring enhances mass transfer but not atomic-level activity. None of them address multi-scale mechanistic synergy. Herein, we design a hierarchically porous P-doped NiCo alloy (hpP-NiCo) with an aim of achieving this synergy via integrating α-FCC/ε-HCP phases, P-induced defects, and 3D porosity. The formed α/ε interface tunes the d-band center to balance H adsorption and water dissociation; and the doped P stabilizes metal-vacancy sites to boost TOF. In addition, porosity matches mass transport with active site accessibility. In 1 M KOH, hpP-NiCo reaches 1000 mA cm^-2 at 185 mV overpotential and has a Tafel slope of 43.1 mV dec^-1, corresponding to electrochemical desorption as the rate-limiting step and verifying Volmer acceleration. Moreover, it also exhibits bifunctional oxygen evolution reaction (OER), achieving 100 mA cm^-2 at potential of 1.55 V. This work establishes a mechanistic synergy model for non-precious HER catalysts.