Copper oxide thin films as components for heterojunction formation with TiO2 for photocatalytic CO2 reduction

Abstract

The activity of copper oxide under irradiation is majorly attributed to the shape and purity of the synthesized materials. To achieve these characteristics, magnetron sputtering was introduced as an efficient technique. Although the stability of these materials is low in photoelectrochemical water splitting, they can be reasonably stable in CO₂ reduction. However, their activity is low due to the high charge recombination rate. Designing heterojunction architectures can be an efficient approach to achieving high activity in CO₂ reduction by increasing the lifetime of photogenerated excitons and decreasing the charge recombination rate. This study presents Cu_xO photocatalysts as promising candidates for creating the heterojunction structure with TiO₂. The thin copper oxide films were obtained with magnetron sputtering and successive ionic layer adsorption and reaction (SILAR) methods. The pristine and heterojunction bilayer films were profoundly investigated. The oxidation states of copper, crystalline form, and morphology of copper oxide and their heterojunction films were studied thoroughly. Furthermore, the photogenerated charges’ fate and direction in the heterojunction bilayer films were studied with the measured surface photovoltage (SPV), employing a Kelvin probe. The SPV and ToF-SIMS analysis confirmed the creation of a junction between copper oxide and titanium dioxide. The photo(electro)catalytic activity of the synthesized materials was studied in solar water splitting and CO₂ reduction. Herein, we additionally report the generation of oxygen during the CO₂ reduction. Moreover, the materials obtained using the SILAR method showed considerably higher activity than those obtained using magnetron sputtering.