Nanostructured Ta3N5 Films as Visible-Light Active Photoanodes for Water Oxidation

• Published in: Journal of physical chemistry. C 2012-09, Vol.116 (36), p.19225-19232
• Main Authors: Dang, Hoang X, Hahn, Nathan T, Park, Hyun S, Bard, Allen J, Mullins, C. Buddie
• Format: Article
• Language: English
• Subjects: Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electrochemistry; Electrodes: preparations and properties; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; General and physical chemistry; Nanocrystalline materials; Physics; Radiation effects on specific materials; Structure of solids and liquids; crystallography
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp307369z

Nanostructured Ta3N5 photoanodes (band gap of ∼2.0 eV) were synthesized via a two-step process: first, nanocolumnar Ta2O5 films were deposited by evaporation of tantalum metal in a vacuum chamber in a low pressure oxygen ambient followed by heating in an ammonia gas flow to convert Ta2O5 into orthorhombic Ta3N5. Under Xe lamp irradiation (∼73 mW/cm2), a 100 nm nanoporous Ta3N5 electrode achieved an anodic photocurrent of ∼1.4 mA/cm2 at +0.5 V versus Ag/AgCl in 1 M KOH solution. By comparison, a dense film achieved ∼0.4 mA/cm2 clearly illustrating the importance of nanostructuring for improving the performance of Ta3N5 photoanodes. However, Ta3N5 films suffered from inherent self-oxidation under light illumination, and application of a cobalt cocatalyst layer was found to improve the stability as well as photocatalytic activity of the Ta3N5 films.