Photoelectrochemical performance and charge dynamics of supersonic cluster beam deposited CuFe2O4 thin films

Developing efficient and stable photoelectrodes is a major challenge in photoelectrochemical energy conversion technologies. Although CuFe2O4 is a promising p-type semiconductor, its implementation as a photocathode has been limited by the difficulty of synthesizing uniform and stable films and by the scarce investigation of its\r\ncharge-transfer kinetics. In this work, a 70 nm thick CuFe2O4 layer was fabricated for the first time by supersonic cluster beam deposition, enabling the direct growth of a homogeneous and nanogranular film on a FTO substrate. After air annealing at 400 ◦C, compositional and structural characterizations revealed the formation of a polycrystalline\r\ntetragonal spinel-type CuFe2O4 film, with a CuxO segregation at the surface. Despite its low thickness, the electrode displayed strong visible light absorption and a p-type photoelectrochemical activity in neutral electrolyte (0.1 M Na2SO4), with a good electrochemical stability. Interestingly, below 0.4 V vs. RHE applied bias, the charge injection kinetic constant drop corresponds to the reduction of Cu2+ surface species to Cu+. The absorbed photon to current conversion efficiency spectra revealed a peak efficiency at 2.8 eV and confirmed a bias-dependent feature associated with the CuxO interfacial layer.