Relation between the nature of the surface facets and the reactivity of Cu2O nanostructures anchored on TiO2NT@PDA electrodes in the photoelectrocatalytic conversion of CO2 to methanol

This paper investigates the influence of morphology of Cu2O nanoparticles (cubes, NcCu2O; spheres, NsCu2O; octahedrons, NoCu2O), deposited on TiO2 nanotubes (TiO2NT) coated with PDA, in the photoelectrocatalytic conversion of CO2 to methanol. At low bias (+0.2 V) a production of 10.0, 6.0 and 5.4 mg L−1 of methanol was obtained for TiO2NT@PDA-NsCu2O, TiO2NT@PDA-NoCu2O, and TiO2NT@PDA-NcCu2O electrodes, with faradaic efficiencies of 27, 39, and 66%, respectively. The conversion to methanol was 357% higher with NcCu2O, compared to the TiO2NT@PDA electrode. The results indicated that both the optical properties and the photocatalytic performance of nanostructures were facet-dependent. The superior catalytic activity of NcCu2O was attributed to the higher concentration of oxygen vacancies on {100} facets, which promotes the activation of CO2 with an energy of −1.2 kcal mol−1. With a lower concentration of oxygen vacancies, CO2 molecule is only physisorbed on {111} facets with an energy of −8.8 kcal mol−1.