High photoelectrochemical water splitting performance on nitrogen doped double-wall TiO₂ nanotube array electrodes

The nitrogen doped double-wall TiO₂ nanotube arrays (N-DW-TiO₂ NTs) have been prepared by a facile two steps electrochemical anodization method, and the nitrogen has been successfully incorporated into the nanotubes in situ anodization process. The unique double walls tubular surface morphology has been achieved by conducting higher anodic voltage in second anodization process than that in the first anodized step. The nitrogen doping and following annealed process in nitrogen atmosphere did not damage the unique, ordered, and vertically aligned structures. Under illumination of simulated solar light (AM 1.5, 100 mW/cm²), the N-DW-TiO₂ NTs presented a high photoelectrochemical water splitting performance, which mainly ascribed to the high surface areas and expended optical absorbance to visible light region. The high surface areas, ordered structure for facilitating electron transfer, and visible light absorbance present the new avenue for improving the solar light application in photoelectrochemical water splitting process for practical hydrogen generation. The N-DW-TiO₂ NTs can be one of promising prototype nanomaterials, and much higher photoconversion efficiency can be expected for the co-doped or sensitized on the N-DW-TiO₂ NTs.