Nanodome Structured BiVO₄/GaO_xN_{1− x} Photoanode for Solar Water Oxidation

A nanodome structured BiVO₄/GaO_xN_{1− x} (BVO/GaON) bilayer photoanode that is prepared by a facile solution method, and that exhibits an improved photoelectrochemical water-oxidation performance is reported. GaON porous nanospheres with an average size of ≈300 nm are first synthesized by a nitridation (NH₃ flow, 800 °C) of Ga₄(OH)₁₀SO₄ nanospheres. The GaON nanospheres are coated by a slurry coating method, and then the BVO layer is uniformly deposited by a sol–gel spin-coating method to form the nanodome structure. Band alignment, light absorption, and relative electrochemical active surface area are investigated to elucidate the advantages of the nanodome structure, using UV–vis spectroscopy, Mott–Schottky analysis, and electrochemical measurements, respectively. It is found that the resulting nanodome structured BVO/GaON photoanode forms a type I heterojunction, in which the GaON layer acts as a hole mirror, and thus reduces interfacial recombination. More importantly, the nanodome structured BVO/GaON exhibits larger electrochemical surface area and improved light absorption properties compared to the planar-type BVO/GaON photoanode, which originates from its unique nanodome structure. When combined with a CoO_x electrocatalyst, the nanodome structured BVO/GaON shows largely improved photocurrent generation (water oxidation activity), and reduced onset potential values.