Earth-Abundant-Based Photocatalysts for Efficient and Selective H₂ Production through Reforming of Formic Acid under Visible Light

Abstract

Hydrogen is considered one of the most promising future solar fuels. Nowadays, particular attention is directed to H2 production through the photoreforming of formic acid (FAc). However, acceptable conversion of FAc into H2 is usually observed only at relatively high temperatures or in the presence of expensive noble metal catalysts. In this study, Cu2O was combined with selected semiconducting metal oxide, namely, CuO, CeO2, Fe2O3, Cu–Fe–O spinel, Nb2O5, TiO2, and Fe3O4, and applied for FAc dehydrogenation at room temperature under visible irradiation. It was found that the type of semiconductor has a significant impact both on the activity and reaction selectivity of the Cu2O-based catalysts. A synergetic activity with the highest FAc conversion (9.89 mmol·g–1·h–1) and selectivity to H2 (>99%) was observed for the Earth-abundant Cu2O/Fe3O4 composite. This synergetic enhancement, with respect to monocomponent ones, originates from an efficient separation of the photogenerated charge carrier according to Z-scheme mechanism accompanied by an in situ restructuring of Cu2O into Cu0/Cu2O. In addition, as-formed Cu0 particles, resulting from the restructuring, are found to be an active component responsible for highly efficient H2 production over Cu2O/Fe3O4. The density functional theory calculations confirm this hypothesis and highlight the role of Cu0 in the reaction mechanism.