Solution-Processed Synthesis of Copper Oxide (Cu O) Thin Films for Efficient Photocatalytic Solar Water Splitting

This article reports a solution-processed synthesis of copper oxide (Cu O) to be used as a potential photocathode for solar hydrogen production in the solar water-splitting system. Cu O thin films were synthesized through the reduction of copper iodide (CuI) thin films by sodium hydroxide (NaOH), which were deposited by the spin coating method from CuI solution in a polar aprotic solvent (acetonitrile). The phase and crystalline quality of the synthesized Cu O thin films prepared at various annealing temperatures were investigated using various techniques. The X-ray diffraction and energy dispersive X-ray spectroscopy studies confirm the presence of Cu₂O, CuO/Cu₂O mixed phase, and pure CuO phase at annealing temperatures of 250, 300, and 350 °C, respectively. It is revealed from the experimental findings that the synthesized Cu O thin films with an annealing temperature of 350 °C possess the highest crystallinity, smooth surface morphology, and higher carrier density. The highest photocurrent density of -19.12 mA/cm² at -1 V versus RHE was achieved in the photoelectrochemical solar hydrogen production system with the use of the Cu O photocathode annealed at a temperature of 350 °C. Therefore, it can be concluded that Cu O synthesized by the spin coating method through the acetonitrile solvent route can be used as an efficient photocathode in the solar water-splitting system.