Synergetic Electrocatalytic Effects of Cu2O-TiO2 Heterostructures in a Solar Driven PEC Device for CO2 Reduction to >C1 Chemicals

Abstract

A solar driven photo-electro-catalytic (PEC) device for CO₂ reduction/water oxidation is here presented. The electrodes are engineered to be used in the n-type configuration, without using precious metals or rare/expensive raw materials. Specifically, the photoanode for water oxidation is made of TiO₂ nanotube arrays prepared via controlled anodic oxidation, while Cu₂O-TiO₂ heterostructures, synthesised by ultra-sonicated assisted co-precipitation and then spray-coated over a carbon-based gas diffusion layer (GDL), are used as electrocathode materials for CO₂ reduction. All the tests are performed without applying external bias or adding sacrificial donors, in a compact homemade PEC reactor in comparison with a conventional slurry photoreactor. The catalytic performances are evaluated in terms of formic acid and acetic acid production, the latter involving the formation of C-C bond. The effect of the presence of TiO₂ is investigated in comparison with a bare cuprous oxide (Cu₂O) film. Results for the bare Cu₂O/GDL electrode (no TiO₂) show 31.8 and 80.6 µmol h^-1 g_Cu^-1 as formic acid and acetic acid production rates, respectively. Cu₂O-TiO₂/GDL electrode, instead, shows more than one order of magnitude higher productivity (0.69 and 2.59 mmol h^-1 g_Cu^-1, respectively). The Faradaic efficiency (FE) to acetic acid is much higher for Cu₂O-TiO₂/GDL electrodes (61.9 %) considering the higher number of electrons involved for acetic acid with respect to formic acid (8 vs. 2). This behaviour can be ascribed to the synergetic electrocatalytic effects of the as-formed Cu₂O-TiO₂ heterostructures, favouring the formation of C-C bond for the sustainable production of >C1 chemicals and fuels.