Highly stable copper oxide composite as an effective photocathode for water splitting via a facile electrochemical synthesis strategy

TLDR

Photoelectrochemical water splitting with solar light is a clean, efficient route to hydrogen, yet most research has focused on n‑type metal oxide photoanodes, leaving p‑type photocathodes largely unexplored. The study aims to fabricate highly efficient, stable Cu₂O/CuO composite photocathodes using a simple two‑step electrochemical method. The composite is produced by electrodepositing Cu on ITO, anodizing to form a Cu₂O layer with a protective CuO film, and calcining; adjusting deposition potential and anodization current tailors composition and crystal orientation for enhanced PEC performance. The Cu₂O/CuO composite with Cu₂O (220) orientation delivers a stable −1.54 mA cm⁻² photocurrent at 0 V vs RHE under AM 1.5G, more than twice the bare Cu₂O, with 74.4 % stability versus 30.1 %, due to CuO’s corrosion protection and recombination inhibition.

Abstract

Hydrogen generation through photoelectrochemical (PEC) water splitting using solar light as an energy resource is believed to be a clean and efficient way to overcome the global energy and environmental problems. Extensive research effort has been focused on n-type metal oxide semiconductors as photoanodes, whereas studies of p-type metal oxide semiconductors as photocathodes where hydrogen is generated are scarce. In this paper, highly efficient and stable copper oxide composite photocathode materials were successfully fabricated by a facile two-step electrochemical strategy, which consists of electrodeposition of a Cu film on an ITO glass substrate followed by anodization of the Cu film under a suitable current density and then calcination to form a Cu2O/CuO composite. The synthesized Cu2O/CuO composite was composed of a thin layer of Cu2O with a thin film of CuO on its top as a protecting coating. The rational control of chemical composition and crystalline orientation of the composite materials was easily achieved by varying the electrochemical parameters, including electrodeposition potential and anodization current density, to achieve an enhanced PEC performance. The best photocathode material among all materials prepared was the Cu2O/CuO composite with Cu2O in (220) orientation, which showed a highly stable photocurrent of −1.54 mA cm−2 at a potential of 0 V vs reversible hydrogen electrode at a mild pH under illumination of AM 1.5G. This photocurrent density was more than 2 times that generated by the bare Cu2O electrode (−0.65 mAcm−2) and the stability was considerably enhanced to 74.4% from 30.1% on the bare Cu2O electrode. The results of this study showed that the top layer of CuO in the Cu2O/CuO composite not only minimized the Cu2O photocorrosion but also served as a recombination inhibitor for the photogenerated electrons and holes from Cu2O, which collectively explained much enhanced stability and PEC activity of the Cu2O/CuO composite. Thus, the electrochemical strategy proposed in this study for the synthesis of the Cu2O/CuO composite opens a new way to use copper oxides as photocathode materials in PEC cells for a highly stable and effective water splitting.