LAUSR

Abstract Copper oxide (CuxO) photocathode has received an enormous amount of attention for photoelectrochemical (PEC) green fuel generation, such as hydrogen, methane, ethane, methanol, and ethanol. Although CuxO is highly photoactive, it is limited by the mismatched charge diffusional length and light absorption depth near the band gap. Recent progress on the effort to alleviate this problem is presented in this review, including the state of the art in morphological modulation of CuxO as a photocathode. While the issue associated with the incongruity of semiconductor property is progressively manageable, another issue related to stability in photoelectrochemical hydrogen evolution reaction (PEC-HER) is rather challenging. Continuous efforts to mitigate the stability issue include multilayer heterojunction, buffer layer, metal doping, and chemical bias. Conversely, the PEC reduction of CO2 (PECRC) is proven to encourage the stability of CuxO because of the reversible phase phenomenon. However, the efficiency remains low owing to the competitive reaction with the hydrogen evolution reaction. Efforts to mitigate this issue are in progress and are also reviewed in this work. A recent PEC performance of all oxide nanostructured CuxO set a new benchmark at par with Cu-based complex heterojunction and a noble metal–toxic element incorporated type of photoelectrode. A low-cost material and fabrication technique for a highly photoactive and stable CuxO photocathode film are expected to be realized for this green application in the near future.