Electrocatalytic and Photoelectrochemical Reduction of Carbon Dioxide at Hierarchical Hybrid Films of Copper(I) Oxide Decorated with Tungsten(VI) Oxide Nanowires

Unique hybrid systems for electroreduction of CO2 under both conventional and visible-light-induced conditions are proposed and designed here by over-coating copper(I) oxide with tungsten(VI) oxide nanowires. When Cu2O and WO3 nanostructures are sequentially deposited on glassy carbon substrate, the resulting system has exhibited high electrocatalytic activity toward reduction of CO2 in phosphate buffer of pH = 6.1. By introducing WO3, the Cu-based system becomes more selective against the competitive hydrogen evolution and exhibits higher CO2-reduction currents relative to the performance of single components. During electroreduction, highly catalytic Cu sites are generated or intercalated within WO3 nanowires partially reduced to mixed-valence hydrogen-absorbing tungsten(VI,V) oxide bronzes, HxWO3, co-existing with sub-stoichiometric tungsten(VI,IV) oxides, WO3-y. Strong adsorption and activation of CO2 molecule has been demonstrated at the WO3-decorated Cu2O interface. Under photoelectrochemical conditions involving illumination with sun-light, the proposed hierarchical system of Cu2O semiconductor deposited onto the transparent fluorine-doped conducting glass electrode and decorated with WO3 nanowires is well-behaved and active toward CO2-reduction in the Na2SO4 neutral medium. In addition to the Cu2O stabilization effect, the heterojunction formed by p-type Cu2O and n-type WO3 semiconductors seems to facilitate charge distribution and separation at the photoelectrochemical interface.