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

Abstract

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.

Time-Retrenched Synthesis of BaTaO2N by Localizing an NH3 Delivery System for Visible-Light-Driven Photoelectrochemical Water Oxidation at Neutral pH: Solid-State Reaction or Flux Method?

“…Such behavior is caused by a charge transfer favored with high overpotentials. Compared with the previously reported photocurrent densities of BaTaO 2 N, 15,52 the photocurrent densities of the BaTaO 2 N samples in this study are lower due to different pH values of electrolyte solutions. It is important to mention that K 3 PO 4 electrolyte (pH = 13) has been used in previous studies, while electrolyte based on Na 2 SO 4 (pH around 7) was used in this study.…”

“…Further, a 4.6 mA•cm −2 photocurrent was yielded for BaTaO 2 N upon combination with Ta 2 N/Ta and modification with CoO x cocatalyst at 1.2 V vs RHE, while 9% incident photon-to-current efficiency (IPCE) at 600 nm was realized during simulated sunlight-driven water oxidation reaction. 15 Annealing of inactive as-synthesized BaTaO 2 N particles in Ar was found to be advantageous to maximize the photocurrent to 6.5 mA•cm −2 at 1.23 V vs RHE, which showed good stability over 24 h (79% initial photocurrent was retained). 16 Very recently, Castelli and co-workers 17 found that the theoretical overpotential of the TaO 2 N-(100) surface of BaTaO 2 N can be effectively decreased to 0.37 V under (photo)electrochemical conditions by applying 1% tensile uniaxial strain.…”

Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial Visible Light-Induced Photocatalytic H2 and O2 Evolution over BaTaO2N

“…13 The CoO x -deposited BaTaO 4.6 mA cm −2 at 1.2 V vs RHE and exhibited a 9% IPCE at 600 nm during water oxidation under simulated sunlight. 14 Further, an unprecedented photocurrent of 6.5 mA cm −2 at 1.23 V vs RHE was achieved for Ar-annealed BaTaO 2 N during sunlightdriven water oxidation. 15 Although the photocatalytic and photoelectrochemical water-splitting efficiencies of BaTaO 2 N have been progressively improved, it is still far from the requirements set for practical applications.…”

Active BaTaO2N photocatalysts prepared from an amorphous Ta2O5 precursor for overall water splitting under visible light

“…This outcome is in agreement with the results obtained from previous photoelectrochemical analyses of BaTaO 2 N electrodes, in which oxygen evolution was enhanced at higher pH values. 20 Fig. 10 plots the apparent quantum yield (AQY) obtained from Rh/Cr 2 O 3 /IrO 2 -loaded BaTaO 2 N, together with the optical absorption of the material.…”