Photoelectrochemical water oxidation over fibrous and sponge-like BiVO4/β-Bi4V2O11 photoanodes fabricated by spray pyrolysis

Two different heterojunction photoanodes were made by one-pot spray pyrolysis deposition of BiVO4/Bi4V2O11 directly onto a conductive FTO substrate or on a previously deposited SnO2 layer onto an FTO substrate (sample BiVO4/Bi4V2O11/SnO2). The direct deposition onto FTO produced fibrous-like BiVO4/Bi4V2O11, whereas the deposition onto SnO2 gave sponge-like BiVO4/Bi4V2O11 morphologies. The photoactivity of these photoelectrodes was investigated for photoelectrochemical water oxidation under visible light irradiation. The fibrous-like BiVO4/Bi4V2O11 exhibited higher photoactivity than that of the sponge-like BiVO4/Bi4V2O11/SnO2 film. The transient photocurrent decay studies revealed that the time of e−/h+ recombination is higher in fibrous-like BiVO4/Bi4V2O11 than sponge-like BiVO4/Bi4V2O11/SnO2 film, which suggests that the electrons might accumulate in the SnO2 layer, thus causing a higher e−/h+ recombination and a lower photoactivity. Electrochemical impedance data showed that the hole transfer from the semiconductor to the water takes place more readily in fibrous-like BiVO4/Bi4V2O11 than sponge-like BiVO4/Bi4V2O11/SnO2 films. Consequently, the overall photoelectrochemical cell efficiencies for fibrous-like BiVO4/Bi4V2O11 and sponge-like BiVO4/Bi4V2O11/SnO2 films were 0.14 and 0.11%, respectively, without using oxygen evolution catalysts. These photoanodes prepared by spray pyrolysis are thus promising for use in PEC water splitting cells.