Investigation of non-stoichiometric delafossite photoelectrodes composed of cuprous oxide and iron oxide for enhanced water-splitting

Photoelectrochemical energy conversion is the ultimate approach for converting sunlight energy into value-added chemical fuels. The path of achieving economically feasible, highly efficient, and earth-abundant material-based photoelectrodes can be a driving force for realizing PEC on a global scale. Copper-based delafossite photoelectrodes are attractive candidates because they exhibit appropriate absorption properties and structural stability in an aqueous system. In this study, delafossite Cu _xFe _2−xO ₂ films of varying compositions ranging from 0 ≤ x ≤ 2 are prepared by adjusting the Cu/Fe composition via radio frequency plasma co-sputtering to evaluate the fundamental optoelectronic properties. The optical bandgap of the CuFeO ₂ films tuned from 1.4 to 1.65 eV, with the maximum carrier concentration of 5.9 × 10 ¹⁷ cm ⁻³ noticed in Cu _1.5Fe _0.5O ₂ film. The X-ray photoelectron spectroscopy measurements confirm the existence of a high level of oxygen-deficient sites in CuFeO ₂ film photoelectrodes that are suitable for PEC performance. The fabricated non-stoichiometric photoelectrode exhibits an excellent hydrogen evolution reaction of 4.3 μmol/hcm ², nearly 1.8 times improvement over Cu ₂ O photoelectrode with a long-term photostability even in an aqueous system. The ability to fabricate tunable electronic structures photoelectrodes along with oxygen-deficient surface defects facilitates to localize band edge closer to the HER of water, and the Fermi level is slightly away from the reduction potential of Cu ₂O, which supports to improve PEC performance by suppressing photo-induced corrosion to retain greater photostability.