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.