 Metastable hexagonal close-pact, HCP, iridium was successfully fabricated on top of metastable HCP nickel by using spherical aberration electron microscopy. This new material showed excellent catalytic properties in the alkaline hydrogen evolution reaction, HER, with a low overpotential of 17 MV at 10 milliampere CM2 and a high specific activity of 8.55 milliampere CM2. Theoretical calculations revealed that the metastable HCP iridium promoted both water adsorption and fast water dissociation, which contributed to its outstanding her activity. These findings suggest that the crystal phase-controlled synthesis of advanced noble metal nanomaterials could be used to develop more efficient catalysts for fundamental catalytic applications. This article was authored by Shi-Ai's Gung, Yu-Jin-Ji, Jechi-Soo, and others.