Photoelectrochemical oxidation of water using La(Ta,Nb)O₂N modified electrodes

Lanthanum tantalum niobium oxynitride [La(Ta,Nb)O₂N] powders were prepared with different Nb/Ta ratios by conventional solid state reaction. La(Ta,Nb)O₂N photoanodes were fabricated by electrophoretic deposition of La(Ta,Nb)O₂N suspension in acetone onto ITO substrate. The La(Ta,Nb)O₂N photoanodes were found to exhibit photoelectrochemical activity for water oxidation reaction in alkaline solution. Subsequently, a cobalt-phosphate based oxygen evolution catalyst (CoPi-OEC) was photodeposited onto the surface of the La(Ta,Nb)O₂N catalyst to improve the photoelectrochemical performance. In the presence of CoPi catalyst, the photocurrent-voltage characteristics of the La(Ta,Nb)O₂N electrodes were enhanced with its effect more pronounced at lower potentials. A stable photocurrent density of 20 mA/cm² at 1.2 V vs SCE was achieved under the illumination using alkaline phosphate solution with pH 13. Relative to the La(Ta,Nb)O₂N photoanodes, nearly three times higher photocurrent density was observed at 1.2 V vs SCE for a CoPi/La(Ta,Nb)O₂N photoelectrode. Perovskite-based oxide-nitrides modified with suitable cocatalyst of CoPi, have been shown as a new pathway towards substantial photoelectrochemical current gain during the PEC water splitting reaction.