Hydrogen production by photoreforming of formic acid in aqueous copper/TiO2 suspensions under UV-simulated solar radiation at room temperature

A new photocatalytic system consisting of two subsystems – Cu⁰/Cl⁻/H⁺/UV_ssr and Cu^II/H⁺/TiO₂/formic acid/UV_ssr – is proposed as a tool to produce hydrogen by reforming an organic species. Formic acid is used as hole scavenger during the experimental runs. An experimental campaign is carried out to demonstrate that the systems can generate hydrogen and to assess how the generation rate depends upon experimental conditions such as copper and TiO₂ loads, chloride and proton ions, and formic acid concentrations. A strong dependence of the Cu⁰/Cl⁻/H⁺/UV_ssr subsystem reactivity upon copper load, chloride concentration and pH is observed. The investigation on the complete system, starting from zero-valent copper, indicates that the addition of TiO₂ and formic acid to the Cu⁰/Cl⁻/H⁺/UV_ssr subsystem does not result into any gain in terms of hydrogen produced and, renders the system totally unreactive under some conditions. On the other hand, when a complete system, starting from cupric ions, is adopted, hydrogen production is observed also for prolonged reaction times with a surplus of hydrogen production with respect to that generated by the Cu⁰/Cl⁻/H⁺/UV_ssr subsystem with the same Cu⁰ starting load and in absence of TiO₂ and sacrificial agent.