Parameter screening of FTO etching and Cu/NiO layers for Cu₂O PEC performance

Efficient utilisation of solar energy is crucial for sustainable power generation, with photoelectrochemical (PEC) water splitting being a promising approach. Cuprous oxide (Cu₂O) is particularly attractive to be utilised as photoelectrodes because of their high efficiency and low cost in relation to other materials despite their poor photostability. Therefore, a novel strategy of protected cuprous oxide photocathode with copper (Cu) underlayer and substrate modification was presented in this preliminary study. The fluorine-doped tin oxide (FTO) substrate etching and copper underlayer will enhance the performance of the cuprous oxide photocathode, while the protected nickel oxide (NiO) layer will improve its stability in the electrolyte. The two-level factorial design was utilised to measure and analyse the effects of FTO etching time, copper electrodeposition (ED) voltage, copper and cuprous oxide ED time, cuprous oxide reduction cycle, nickel ED time, and annealing temperature and time on the photocatalytic activity. The morphological, elemental composition and PEC features of the samples are characterised using field emission scanning electron microscopy and a current–voltage monitoring system. Under 100 mW/cm² of simulated sunlight, the photoelectrode exhibits a maximum current density of −54.53 × 10⁻²mA/cm² at 0 V_RHE.