Mixed‐Valence Atomic‐Layer Iridium Patches Enhance Alkaline Hydrogen Evolution

Engineering structurally defined interfacial motifs between isolated atoms and nanoparticles offers a promising route toward high‐performance electrocatalysis, yet achieving such motifs with clear structure–function correlations remains difficult. Here, iridium (Ir) configurations comprising single atoms (SA), atomic‐layer patches (AL), and nanoparticles (NP) were constructed on tricopper phosphide nanowires as a model platform, yielding Ir SA /Cu 3 P, Ir AL /Cu 3 P, and Ir NP /Cu 3 P, respectively. This configuration‐defined catalyst series reveals distinct structure‐dependent alkaline hydrogen evolution behavior. The atomic‐layer iridium patches exhibit a mixed‐valence interfacial state and anisotropic lattice distortion, as established by complementary microscopy, spectroscopy, and scattering analyses. Theory further reveals an edge‐to‐core charge gradient and indicates that this electronically graded interface optimizes Ir 5d states to facilitate water dissociation and balance hydrogen adsorption/desorption. Consequently, the iridium atomic‐layer catalyst achieves an overpotential of 27 mV at 10 mA cm −2 and reaches 1 A cm −2 at a cell voltage of 1.68 V in an anion exchange membrane electrolyzer. This work establishes mixed‐valence atomic‐layer metal patches as a functional platform for interfacial electrocatalysis.