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 IrSA/Cu3P, IrAL/Cu3P, and IrNP/Cu3P, 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.