Photoelectrochemical water splitting using a photoelectrode is regarded as an alternative production method of hydrogen and expected to eventually replace fossil fuels. As a member of (oxy)nitrides family, BaTaO2N is one of the most attractive oxynitride compounds harvesting visible light up to 660 nm and possessing appropriate band edge potentials for water reduction and oxidation under visible light. As flux coating method allows fabricating the photocatalytic crystal layers with high crystallinity and adhesiveness to the substrate, we have employed a flux coating method using the BaCl2 flux to directly fabricate BaTaO2N photoelectrode in this work. The BaTaO2N crystal layers on Ta substrate were separately fabricated by two routes: (i) powder method and (ii) solution method. In powder method, 1.0 g of Ba(NO3)2 powder as a barium source and 2.0 g of BaCl2 powder as a flux were dry mixed. The well homogenized mixture was put on the top of Ta substrate placed in alumina cell and heated in a horizontal tubular furnace at 1000°C for 2 h under an NH3 flow (200 mL?min-1). In solution method, 200 μL of Ba(NO3)2 aqueous solution (0.1 M) as a barium source and 200 μL of BaCl2 aqueous solution (0.5 M) as a flux were used. The solution-deposited Ta substrate was dried and heated at 850°C for 1 h under an NH3 flow (200 mL?min-1). The XRD and SEM results revealed that the BaTaO2N crystal layers were successfully fabricated by powder- and solution-based flux coating methods on Ta substrate and crystals had a cubic shape with average size of less than 1 μm and 0.5 μm, respectively, as shown in Figure 1. The EDS mapping images confirmed that barium, tantalum, oxygen, and nitrogen were homogenously distributed in the BaTaO2N crystal layers, and the thicknesses of the BaTaO2N crystal layers fabricated by powder- and solution-based flux coating methods were about 5 and 1 μm, respectively.
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