High‐Entropy Topologically Close‐Packed Ir Alloys Enable Interatomic Hydrogen Spillover for Hydrogen Evolution toward High‐Performing Anion Exchange Membrane Water Electrolyzers

Abstract The efficiency of alkaline hydrogen evolution reaction (HER) is strictly restricted by the insufficient active hydrogen supply. Here, we develop high‐entropy topologically close‐packed C15‐(IrRh) 2 PrNdTb nanocrystals with enhanced interatomic hydrogen spillover from oxophilic sites (Pr/Nd/Tb) to nucleophilic sites (Ir/Rh) as efficient HER electrocatalysts for anion exchange membrane water electrolyzers (AEMWEs). Compared to the disordered (A1) counterpart, intermetallic C15‐(IrRh) 2 PrNdTb features a higher coordination number for Pr/Nd/Tb and a more electron‐rich environment for Ir/Rh with compressed Ir–Ir(Rh) bonds. In 1.0 M KOH, C15‐(IrRh) 2 PrNdTb reveals an ultralow HER overpotential of only 8 and 34 mV to reach 10 and 100 mA cm −2 , respectively. The AEMWE with C15‐(IrRh) 2 PrNdTb cathode delivers an industrial‐level current density of 1 A cm −2 at only 1.69 V, and could be operated stably for over 2000 h (64 µV h −1 loss), representing one of the best alkaline HER catalysts ever reported. The markedly enhanced hydrogen adsorption/desorption kinetics on C15‐(IrRh) 2 PrNdTb demonstrates an additional active hydrogen migration step via hydrogen spillover during HER. Density functional theory (DFT) calculations indicate that the strong d ‐ f orbital coupling in C15‐(IrRh) 2 PrNdTb establishes efficient interatomic hydrogen spillover pathways through Pr(Nd/Tb)–Ir(Rh) hollow site to Ir(Rh)–Ir(Rh) bridge site to Ir(Rh)–Ir(Rh) hollow site, thereby accelerating HER kinetics.