Fabrication of BaTaO2N Thin Films by Interfacial Reactions of BaCO3/Ta3N5 Layers on a Ta Substrate and Resulting High Photoanode Efficiencies During Water Splitting

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Thin films of barium tantalum oxynitride (BaTaO2N) with thicknesses of 150–680 nm are grown on TaN/Ta substrates via the interfacial reaction of BaCO3/Ta3N5 layers in a N2 atmosphere. A TaN thin film is first deposited on a Ta substrate by the Ar/N2 ion sputtering of a Ta target, and then covered with a TaOx layer by Ar/O2 sputtering. The TaOx layer is subsequently nitrided in an NH3 flow to a Ta3N5 layer. Finally, Ba metal is deposited on the Ta3N5/TaN/Ta substrate under vacuum, oxidized, and carbonized to produce BaCO3. The interfacial reaction between the BaCO3 and Ta3N5 layers is conducted in a N2 atmosphere at high temperatures. X‐ray diffraction patterns confirm BaTaO2N and Ta2N phases on the Ta substrates, while cross‐sectional scanning electron microscopy images show a three‐layer BaTaO2N/Ta2N/Ta structure. Cobalt oxide (CoOx)‐deposited BaTaO2N/Ta2N/Ta photoanodes for water oxidation provide a high photocurrent of 4.6 mA cm−2 at 1.23 V (vs RHE) and an incident photon‐to‐current conversion efficiency of 9% at 600 nm under simulated AM1.5G irradiation. The efficiency of this photoanode is remarkably improved compared with previously reported photoanode thin films. Interestingly, a BaTaO2N/Ta2N/Ta electrode with similar photoanode performance is also obtained via the interfacial reaction between TaN and BaCO3 layers.