Electrochemical Synthesis and Characterization of p-CuBi2O4 Thin Film Photocathodes

We report the synthesis of visible-light-active thin films of p-CuBi2O4 utilizing electrodeposition for the first time. Bimetallic films of Cu and Bi were deposited from a single bath onto fluorine-doped tin oxide (FTO) substrates and thermally oxidized in air. The effects of deposition parameters such as potential, time, and bath concentration were investigated. In general, the films consisted of interconnected particles roughly 250 nm in diameter and showed an onset of light absorption at 680 nm (1.8 eV). The films were characterized by photoelectrochemical (PEC) techniques in order to provide insight into the critical PEC properties of CuBi2O4 such as flat-band potential, photocurrent stability, and incident photon-to-current efficiency (IPCE). Despite the narrow band gap and quite suitable band edge positions for PEC H2 generation, the films’ stable calculated AM1.5G photocurrents in N2 degassed Na2SO4 were relatively small (44–55 μA/cm2 at −0.2 V vs Ag/AgCl) due to maximum UV quantum yields of ∼1–2% that decreased significantly throughout the visible range, becoming negligible near 700 nm. Film stability tests under constant illumination revealed that the films were unstable in acidic electrolyte (pH 3.5) due to the reduction and dissolution of Cu but were stable in basic electrolyte (pH 10.8) after an initial ∼50% decrease in performance.