The immiscibility of crystallographic facets in multi‐metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face‐centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close‐packed (hcp) Ni is 49.8 %. Hence, in a series of Ni−In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18–20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h−1 H2 is evolved at −385 mV with mass activity of 57.5 A g−1 at—400 mV, 200 h stability at −0.18 V versus reversible hydrogen electrode (RHE), and Pt‐like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH− ions and the prevention of catalyst poisoning.

The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H 2 production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of NiÀ In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18-20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni 0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h À 1 H 2 is evolved at À 385 mV with mass activity of 57.5 A g À 1 at-400 mV, 200 h stability at À 0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH À ions and the prevention of catalyst poisoning.