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

Abstract

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 CuxFe2−xO2 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 CuFeO2 films tuned from 1.4 to 1.65 eV, with the maximum carrier concentration of 5.9 × 1017 cm−3 noticed in Cu1.5Fe0.5O2 film. The X-ray photoelectron spectroscopy measurements confirm the existence of a high level of oxygen-deficient sites in CuFeO2 film photoelectrodes that are suitable for PEC performance. The fabricated non-stoichiometric photoelectrode exhibits an excellent hydrogen evolution reaction of 4.3 μmol/hcm2, nearly 1.8 times improvement over Cu2O 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 Cu2O, which supports to improve PEC performance by suppressing photo-induced corrosion to retain greater photostability.