Boosting carrier separation and transport in CuGaO2 photocathodes by coupled effects of surface polarization and facet-junction

[Display omitted] •Flower-like micro-nano hierarchical structure CuGaO2 microspheres have been easily prepared by one-pot hydrothermal method.•CuGaO2 microspheres are self-assembled from nanosheets by electrostatic force.•CuGaO2 nanosheets as building blocks show prominent surface polarization effects.•The facet-junction that is formed by the crossed CuGaO2 nanosheets can promote the collection of photo-generated carriers.•Flower-like CuGaO2 microspheres combine nanoscale surface polarization effect and microscale facet-junction effect. This study investigates the synergistic enhancement of carrier separation and transport in CuGaO2 photocathodes, achieved through the coupled effects of surface polarization and facet-junction engineering. Delafossite CuGaO2 microspheres, which exhibit a flower-like micro-nano hierarchical structure, are synthesized facilely through a one-pot hydrothermal process. These microspheres self-assemble from CuGaO2 nanosheets, driven by electrostatic forces among crystal facets. Morphology and size are systematically modulated by pH values, solvent composition, and reaction temperature. The CuGaO2 nanosheets, serving as fundamental building blocks, manifest notable surface polarization effects that facilitate the efficient transport of photo-generated carriers. The facet-junction formed between intersecting CuGaO2 nanosheets facilitates the collection of photo-generated electrons and holes on both sides of the interface, leading to spatial separation. Consequently, the CuGaO2 microspheres synergistically combine nanoscale surface polarization and microscale facet-junction effects, promoting the effective separation and rapid transport of electron-hole pairs generated under visible-light irradiation. The resulting simple bare photocathode, constructed using CuGaO2 microspheres, demonstrates a photocurrent density of 32 μA/cm2 at zero-bias, with a peak incident photon-to-current efficiency of 12.72 % at a 450 nm wavelength. Further optimization of the CuGaO2 photocathode yields a better photocurrent density of 138 μA/cm2 at 0.33 VRHE. These results underscore the significance of integrating nanoscale surface polarization effects with microscale facet-junction effects to achieve efficient separation and rapid transport of photo-generated carriers in photoelectrochemical cells.