Aligned Fe2TiO5-containing nanotube arrays with low onset potential for visible-light water oxidation.

There remains a pressing challenge in the efficient utilization of visible light in the photoelectrochemical applications of water splitting. Here, we design and fabricate pseudobrookite Fe2TiO5 ultrathin layers grown on vertically aligned TiO2 nanotube arrays that can enhance the conduction and utilization of photogenerated charge carriers. Our photoanodes are characterized by low onset potentials of ~0.2 V, high photon-to-current efficiencies of 40-50% under 400-600 nm irradiation and total energy conversion efficiencies of ~2.7%. The high performance of Fe2TiO5 nanotube arrays can be attributed to the anisotropic charge carrier transportation and elongated charge carrier diffusion length (compared with those of conventional TiO2 or Fe2O3 photoanodes) based on electrochemical impedance analysis and first-principles calculations. The Fe2TiO5 nanotube arrays may open up more opportunities in the design of efficient and low-cost photoanodes working in visible light for photoelectrochemical applications.