Interstitial-Hydrogen-Modulated Subnanometer PdPtIrCoNiH High-Entropy Hydride Nanowires for Efficient Hydrogen Electrocatalysis

The slow Volmer step (water dissociation/formation) poses a fundamental challenge in alkaline hydrogen electrocatalysis. Here, we demonstrate that the integration of high-entropy design and interstitial hydrogen engineering in PdPtIrCoNiH 15 high-entropy hydride nanowires effectively overcomes this kinetic limitation. The PdPtIrCoNiH 15 nanowire catalyst (diameter ca. 1.21 nm) exhibits remarkable mass activities of 8.02 and 4.55 A mg PGM –1 at an overpotential of 0.05 V for the hydrogen oxidation reaction (HOR) in 0.1 M KOH and the hydrogen evolution reaction (HER) in 1.0 M KOH, respectively, outperforming commercial Pt/C and other control catalysts. Operando X-ray spectroscopies reveal that interstitial H induces lattice expansion in PdPtIrCoNiH 15 and buffers the structural distortion, which can promote water dissociation/*OH adsorption and boost catalytic activity/structural reversibility. Density functional theory (DFT) calculations reveal the gradient distribution of *H/*OH binding energy (HBE/OHBE) on the PdPtIrCoNiH 15 surface. The high-entropy effect and interstitial hydrogen could cause electron richness and deficiency on the Pd/Pt and Ir/Co/Ni sites, thus optimizing the HBE and OHBE on these sites, respectively. The gradient adsorption and optimized HBE/OHBE enable favorable channels for *H migration and lower the energy barrier of the Volmer step, thereby improving the catalytic activity. In an anion-exchange membrane fuel cell (AEMFC), the PdPtIrCoNiH 15 anode achieves a remarkable peak power density of 1.37 W cm –2 . As an AEM water electrolyzer (AEMWE) cathode, it requires only 1.626 V to reach 1 A cm –2 and maintains a slow degradation rate of 71 μV h –1 over 1000 h, representing one of the most active alkaline hydrogen electrocatalysts reported.