High-entropy alloys in a radial mesostructured TiO2 support for efficient hydrogen evolution.

High-entropy alloys (HEAs) have emerged as promising electrocatalysts as their multi-element synergistic effects and tunable electronic structures offer unusual opportunities to optimize catalytic pathways while reducing noble-metal usage. However, HEA nanoparticles still suffer from aggregation during synthesis and structural degradation during long-term electrochemical operation, which severely limits their practical performance. Here, a spatial confinement strategy that combines cooperative self-assembly with a solvothermal process is developed to uniformly encapsulate PtCuFeCoNi HEA nanoparticles within radially ordered mesoporous TiO2 channels, affording a composite catalyst denoted as HEA-meso-TiO2. Benefiting from the synergistic interplay of HEA composition, mesoporous confinement, strong metal-support interaction, and rapid mass transport, HEA-meso-TiO2 exhibits outstanding hydrogen evolution reaction (HER) activity in alkaline electrolyte, requiring an overpotential of only 31 mV at 10 mA cm-2, together with a low Tafel slope of 24 mV dec-1 and excellent durability over 200 h. The catalyst also shows favorable hydrazine oxidation kinetics and enables energy-efficient overall hydrazine splitting when employed as both the anode and the cathode. At 1000 mA cm-2, the cell voltage is reduced by 1.25 V compared to conventional overall water splitting, while stable operation is maintained for 50 h at high current densities. This work establishes a viable strategy for integrating high-entropy alloys with ordered mesoporous oxide supports toward highly active and durable electrocatalysts for energy-saving hydrogen production.