Atomic doping to enhance the p-type behavior of BiFeO3 photoelectrodes for solar H2O2 production

BiFeO3 is a semiconductor with a bandgap of similar to 2.2 eV and with conduction band minimum (CBM) and valence band maximum (VBM) positions straddling the water reduction and oxidation potentials. These features make BiFeO3 a promising photoelectrode candidate for use in a photoelectrochemical cell for solar fuel and chemical production. Previous studies have shown that both n-type and p-type BiFeO3 can be obtained without intentional extrinsic doping, which means that both donor- and acceptor-type defects can form readily. In this study, we prepared and compared p-type BiFeO3 with intrinsic doping (acceptor levels created by Bi vacancies) and extrinsic doping (acceptor levels created by substitutional doping of Na+ at the Bi3+ site) to understand their differences using combined experimental and computational studies. We show that Na-doped BiFeO3 can generate a significantly higher cathodic photocurrent density because Na doping enhances both photon absorption and electron-hole separation. Our computational results provide a microscopic understanding of their origins. We also demonstrate the use of a Na-doped BiFeO3 photocathode with Ag nanoparticle catalysts for solar O-2 reduction to H2O2 and evaluate how much photovoltage can be gained by the use of Na-doped BiFeO3 photocathode.