Homogeneous Metastable Hexagonal Phase Iridium Enhances Hydrogen Evolution Catalysis

Catalytic reactions are surface‐sensitive processes. Fabrication of homogeneous metastable metals can be used to promote phase‐dependent catalytic performance; however, this has been a challenging task. Herein, homogeneous metastable hexagonal close‐packed (hcp) Ir is epitaxially grown onto metastable phase hcp Ni, as demonstrated using spherical aberration electron microscopy. The as‐fabricated metastable hcp Ir exhibits high intrinsic activity for the alkaline hydrogen evolution reaction (HER). In particular, metastable hcp Ir delivers a low overpotential of 17 mV at 10 mA cm(−2) and presents a high specific activity of 8.55 mA cm(−2) and a high turnover frequency of 38.26 s(−1) at −0.07 V versus the reversible hydrogen electrode. Owing to its epitaxially grown structure, metastable hcp Ir is highly stable. Theoretical calculations reveal that metastable hcp Ir promotes H(2)O adsorption and fast H(2)O dissociation, which contributes to its remarkable HER activity. Findings can elucidate the crystal phase‐controlled synthesis of advanced noble metal nanomaterials for the fundamental catalytic applications.