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

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)2PrNdTb 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)2PrNdTb 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)2PrNdTb 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)2PrNdTb 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)2PrNdTb 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)2PrNdTb 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.