Photoelectrochemical reduction of CO2: Stabilization and enhancement of activity of copper(I) oxide semiconductor by over-coating with tungsten carbide and carbide-derived carbons

Hybrid photocathode materials, which are composed of hierarchically deposited (onto the transparent fluorine-doped conducting glass electrode) copper(I) oxide (inner layer) and robust carbon structures, such as carbide derived carbons (CDC) or mixture of CDC with 70% (weight) tungsten carbide (WC-CDC), have been fabricated and examined using electrochemical methods, X-ray diffraction and various spectroscopic approaches including Raman technique. The resulting systems have been characterized by good stability and have exhibited high photoelectrochemical activity toward reduction of CO2 upon illumination with sunlight in the Na2SO4 neutral medium. While the semiconducting properties of Cu2O are not largely affected by the interfacial modification with CDC and WC-CDC, the photostability of the hybrid photocathode is significantly improved. The stabilization effect should reflect the capacitive properties of CDC and WC-CDC. The capability of CDC and WC-CDC over-layers to undergo efficient double-layer-type charging/discharging should facilitate collection and transport of photoelectrons and inhibit recombination of photogenerated electron-hole pairs. The relatively higher photoelectrochemical activity of the Cu2O system over-coated with WC-CDC, relative to the one containing CDC only, seems to reflect specific interactions between CO2 and WC-CDC thus inducing reduction of CO2 adsorbates.