Electron-enriched Co-Eu-B nanoclusters confined in mesoporous Al2O3 enable ultrafast room-temperature NaBH4 hydrolysis

Amorphous Co-Eu-B nanoclusters confined in mesoporous Al 2 O 3 were fabricated by an impregnation–chemical-reduction route. Their hydrogen-evolution performance during NaBH 4 hydrolysis was benchmarked against Co-B and Eu-modified Co-B analogues. Structure-activity correlations reveal a three-fold synergy. Geometric confinement by the Al 2 O 3 scaffold prevents nanoparticle agglomeration. Mixed-valent Eu 3+ /Eu 2+ injects electrons into Co via concurrent B → Co and Eu → Co pathways, generating an electron-rich Co δ− core. The Eu-Al-O interface markedly increases Lewis-acid site density, facilitating H 2 O polarization and B-H bond cleavage. Owing to this coupling, the optimised Co-Eu-B/Al 2 O 3 catalyst (Eu/Co = 0.17) delivers a peak hydrogen-generation rate of 2987.81 mL min −1 g −1 at 30 °C, lowers the apparent activation energy to 39.21 kJ mol −1 , and retains full activity over five consecutive cycles-outperforming previously reported Co-based systems. The study elucidates, for the first time, how rare-earth dopants and support engineering co-operate through structural, electronic and acid–base regulation, providing a transferable blueprint for low-cost, highly active and durable hydrolysis catalysts suitable for portable fuel cells and distributed hydrogen technologies.