Enhanced solar water splitting using bismuth ferrite photoanodes grown by direct liquid injection chemical vapor deposition

Near-stoichiometric, Fe-rich, and Bi-rich bismuth ferrite (BiFeO3) thin films have been deposited on fluorine doped tin oxide (FTO) coated glass substrates using the direct liquid injection chemical vapor deposition (DLI-CVD) technique. While near-stoichiometric films exhibit the expected X-ray diffraction (XRD) pattern of mostly pure BiFeO3, the Fe-rich samples contain mixed phases of Bi2Fe4O9 and BiFeO3. In comparison, the XRD pattern of Bi-rich BiFeO3 (BFO–B) samples show mixed phases of Bi2O3 and Bi25FeO40 in addition to BiFeO3. Photoelectrochemical characteristics of the three samples have been investigated, with the Fe-rich films exhibiting improved performance as compared with near-stoichiometric and Bi-rich BFO films. The Fe-rich film, containing additional Bi2Fe4O9 phase, shows a red shift in the absorption edge leading to higher visible range absorption that increases the charge separation efficiency as compared to BFO–S and BFO–B. The BFO–F photoanode shows an optimized photocurrent density of 0.47 mA/cm2 at 1.23 V vs RHE as compared to 0.44 mA/cm2 for BFO–S and a very low value (<0.02 mA/cm2) for BFO–B. The incident photon-to-current conversion efficiency (IPCE) at 420 nm are found to be ∼18% and ∼17.5% and ∼13% for BFO–F, BFO–S and BFO–B, respectively. Overall, this work suggests that BFO electrodes containing mixed but opto-electronically active phases of BiFeO3 and Bi2Fe4O9 are promising electrodes for photoelectrochemical water splitting.