Visible-light-induced electron density enrichment of the active sites in the core-satellite structured CuWO4@NiO for fast hydrogen generation from ammonia borane methanolysis

Abstract

Catalytic dehydrogenation of ammonia borane (AB) is an integrated technology for producing hydrogen with promising applications in mobile fuel cells. However, its commercial prospect is significantly hampered by the high expenditure of precious metal catalysts. Herein, a low-cost and efficient Z-schemed core-satellite structured CuWO4@NiO nanocomposite catalyst was developed for the methanolysis of AB for fast hydrogen production. The experimental and theoretical calculation results revealed charge transfer between CuWO4 (core) and NiO (satellite), thus creating active Ni and Cu sites for the adsorption and activation of methanol and AB, respectively. When the CuWO4@NiO catalyst was irradiated with visible light, numerous photogenerated electrons were accumulated in the conduction band of NiO of CuWO4@NiO by virtue of the special Z-scheme heterojunction, resulting in the electron density enrichment of Ni sites. The electron-enriched Ni sites effectively activated the adsorbed methanol, thus making the O–H bond cleavage easier, which was identified as the rate-determining step in AB methanolysis using kinetic isotope effect experiments. Based on the special electronic and energy band structures, our CuWO4@NiO catalyst exhibited outstanding catalytic activity with a turnover frequency of 26.5 min−1 in AB methanolysis, surpassing most noble-metal-free catalysts reported in the literature. Our findings show that visible light can be applied as a useful tool to optimize the electronic states of both active sites of catalysts and adsorbed reactants. This study provides insight into the design of more efficient catalytic systems toward AB methanolysis for fast hydrogen evolution.