Plasma Electrolytic Oxidation Synthesis of Heterostructured TiO 2 /Cu x O Films for Photoelectrochemical Water Splitting Applications

TiO 2 is a versatile photo-/electrochemically active material that finds a wide variety of applications in industry and science alike. Its main but often overlooked advantage is the abundance of Ti in nature, as it is the 9th most commonly found element in the Earth’s crust. Despite some drawbacks (e.g., large band gap) that limit its light conversion efficiency in comparison to some other materials, it is particularly inert in corrosive media, and its properties can be modified by various means. In this study TiO 2 films are synthesized by an anodization-like procedure called plasma electrolytic oxidation. By varying synthesis conditions different morphologies and structures are obtained. Moreover, successful heterostructuring is achieved by adding a copper precursor into the solution. The TiO 2 /Cu x O films are comprehensively characterized for their structural, optical, and photoelectrochemical properties. Interpretation of XPS and XANES spectra suggest that the content of Cu 2+ increases in relation to the maximum voltage reached during synthesis. The UV–vis absorption was also found to display a distinct Cu 2+ absorption footprint, as well as lower optical band gap values for the heterostructures. A comprehensive photoelectrochemical characterization for water splitting in 1 M KOH reveals that the TiO 2 /Cu x O films exhibit improved activity overall.