Enhanced Stability and Photoelectrochemical Performance of Cu₂O-Based Photoelectrodes via In Situ Activation and Sequential Photodeposition of Protective Overlayer

Cuprous oxide (Cu₂O) is a promising p-type semiconductor material for solar energy conversion due to its earth-abundant nature and suitable bandgap (2 eV), corresponding to a theoretical photocurrent density of 14.7 mA cm^-2 upon integration of AM 1.5 illumination. However, its practical utilization is significantly hindered by severe photocorrosion and poor charge carrier dynamics. In this study, we demonstrate the activation of Cu₂O photoelectrodes through applied bias and solar irradiation, leading to the formation of a Cu₂O/CuO heterojunction (a-Cu₂O) that enhances charge separation and improves PEC performance. The a-Cu₂O photoelectrode exhibited anodic photocurrent generation under light irradiation, along with an anodic shift in the hydrogen evolution reaction (HER) onset potential by 200 mV. Using this n-type behavior, an iron oxyhydroxide (FeOOH) overlayer was deposited by photodeposition technique onto the a-Cu₂O surface to further enhance the stability of a-Cu₂O, forming the a-Cu₂O/FeOOH photoelectrode. FeOOH functioned both as a cocatalyst and a protective layer, effectively inhibiting the self-reduction and self-oxidation of Cu⁺ species. Structural and surface analyses using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) confirmed the formation of the Cu₂O/CuO heterojunction and successful FeOOH deposition. Linear sweep voltammetry (LSV) and chronoamperometry measurements demonstrated significantly improved photocurrent stability and performance in the a-Cu₂O/FeOOH photoelectrode, showing a 2-fold increase in photocurrent density at +0.5 V vs RHE compared to the bare Cu₂O electrode. This study presents a simple yet effective approach for improving both the PEC activity and stability of Cu₂O-based photoelectrodes through in situ activation and photodeposition techniques. The findings offer valuable insights into heterojunction engineering and protective layer strategies, contributing to the development of more efficient and durable Cu₂O-based photocathodes for solar-driven water splitting and other PEC applications.