Fabrication of BaTaO_2N Thin Films by Interfacial Reactions of BaCO_3/Ta_3N_5 Layers on a Ta Substrate and Resulting High Photoanode Efficiencies During Water Splitting

摘要

Thin films of barium tantalum oxynitride (BaTaO_2N) with thicknesses of 150–680 nm are grown on TaN/Ta substrates via the interfacial reaction of BaCO_3/Ta_3N_5 layers in a N_2 atmosphere. A TaN thin film is first deposited on a Ta substrate by the Ar/N_2 ion sputtering of a Ta target, and then covered with a TaO_x layer by Ar/O_2 sputtering. The TaO_x layer is subsequently nitrided in an NH_3 flow to a Ta_3N_5 layer. Finally, Ba metal is deposited on the Ta_3N_5/ TaN/Ta substrate under vacuum, oxidized, and carbonized to produce BaCO_3. The interfacial reaction between the BaCO_3 and Ta_3N_5 layers is conducted in a N_2 atmosphere at high temperatures. X-ray diffraction patterns confirm BaTaO_2N and Ta_2N phases on the Ta substrates, while cross-sectional scanning electron microscopy images show a three-layer BaTaO_2N/Ta_2N/Ta structure. Cobalt oxide (CoO_x)-deposited BaTaO_2N/Ta_2N/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 BaTaO_2N/Ta_2N/Ta electrode with similar photoanode performance is also obtained via the interfacial reaction between TaN and BaCO_3 layers.