Ta-Doped porous TiO ₂ nanorod arrays by substrate-assisted synthesis: efficient photoelectrocatalysts for water oxidation

Owing to its excellent chemical stability and low cost, titanium dioxide (TiO₂) has been widely studied as a photoanode for photoelectrochemical (PEC) water splitting. However, TiO₂'s practical applications in solar energy-to-synthetic fuel conversion processes have been constrained by its inherently poor ability to transport photogenerated electrons and holes. In this paper, we report Ta-doped porous TiO₂ nanorod arrays on Ta foil (Ta-PTNA) that do not possess this issue and that can thus efficiently photoelectrocatalyze water oxidation, helping the production of H₂ (a clean fuel) from water at the expense of solar light. The materials are synthesized by a new, facile synthetic approach involving the hydrothermal treatment of a TiO₂ precursor with Ta foil, without seeds and templates, and followed by calcination of the product. Besides serving as a source of Ta dopant atoms, Ta foil is found to play a vital role in the formation of nanopores in the materials. The material obtained with hydrothermal treatment at 180 °C for 10 h (Ta-PTNA-10), in particular, affords very large photocurrent density and very high photoconversion efficiency (0.32% at 0.79 V vs. RHE, which is better than those of many previously reported photocatalysts and ∼4 times larger than that of undoped TiO₂ nanorod arrays). Ta-PTNAs' remarkable PEC catalytic performance is found to be due to their nanoporous structure and high electronic conductivity.