Cu/TiO₂ as a low-cost alternative to Pt/TiO₂ for hydrogen production via photocatalytic ethanol reforming: a direct comparison and mechanistic analysis

TiO₂ is one of the most studied photocatalysts for hydrogen evolution. As decoration with a metal co-catalyst is essential for catalytic formation of hydrogen, there is an ongoing search for low-cost alternatives to the currently predominant noble metals. In this work, we directly compare Cu and Pt co-catalysts on anatase TiO₂ in liquid ethanol photoreforming in the absence of water and oxygen. Under these conditions, high product selectivities are achievable on the carbonaceous side of the reaction. The activity of Cu is in the same order of magnitude as Pt, which makes Cu a prospective candidate. Our results also indicate that low metal loadings might be favorable to achieve high co-catalyst efficiencies. Additional insights into the photocatalyst behavior under reaction conditions complement the photocatalytic investigation. Namely, color changes and absorbance features in the visible indicate a reduction of both TiO₂ and the Cu co-catalyst when excluding water and oxygen from the reaction solution. The surface hydroxyls formed during the photooxidation of the alcohol likely take part in these processes, which can be comprehensively explained when considering previous insights from UHV experiments. Consequently, this work not only suggests Cu to be a suitable and cost-efficient replacement for Pt as a co-catalyst for hydrogen evolution but also indicates that surface hydroxyls might play a decisive role in complex photocatalytic reactions on TiO₂ in a liquid environment.