Plasma Electrolytic Oxidation Synthesis of Heterostructured TiO₂/Cu_xO Films for Photoelectrochemical Water Splitting Applications

Abstract

TiO2 is a versatile photo-/electrochemically active material that finds a wide variety of applications in industry and science. Its main but often overlooked advantage is the abundance of Ti in nature, as it is the ninth 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 other materials, it is particularly inert in corrosive media, and its properties can be modified by various means. In this study TiO2 films were synthesized by an anodization-like procedure called plasma electrolytic oxidation. By varying synthesis conditions, different morphologies and structures were obained. Moreover, successful heterostructuring was achieved by adding a copper precursor to the solution. The TiO2/CuxO films were comprehensively characterized for their structural, optical, and photoelectrochemical properties. Interpretation of X-ray phototelectron and X-ray absorption near edge spectra suggest that the content of Cu2+ increases in relation to the maximum voltage reached during synthesis. UV-Vis absorption spectra were also found to display a distinct Cu2+ absorption footprint, as well as lower optical band gap values for the heterostructures. A comprehensive photoelectrochemical characterization for water splitting in 1 M KOH revealed that the TiO2/CuxO films exhibit improved activity overall.