Fabrication of an Efficient BaTaO₂N Photoanode Harvesting a Wide Range of Visible Light for Water Splitting

Abstract

Photoanodes made from BaTaO2N that can harvest visible light up to 660 nm wavelength were fabricated on Ti substrates for achieving efficient water splitting. Both pre-treatment of BaTaO2N particles with an H2 stream and post-necking treatment with TaCl5 effectively increased the photocurrent due to the decreased electrical resistance in the porous BaTaO2N photoanode. A combination of pre-loading of CoO(x) on the BaTaO2N particles and post-loading of RhO(x) significantly improved both the photocurrent and stability under visible light irradiation, along with an obvious negative shift (ca. 300 mV) of the onset potential for water oxidation, while sole loading resulted in a lower photocurrent or insufficient stability. The IPCE value was estimated to be ca. 10% at 1.2 V vs RHE under 600 nm, which is the highest among photoanode materials that can harvest light beyond 600 nm for water oxidation. Photoelectrochemical water splitting into H2 and O2 under visible light was demonstrated using RhO(x)/CoO(x)/BaTaO2N/Ti photoanodes under an externally applied bias larger than 0.7 V to a Pt counter electrode.