Ternary Ti–Mo–Ni mixed oxidenanotube arrays as photoanode materials for efficient solar hydrogen production

Abstract

To date, most studies on the fabrication and development of photoelectrodes for solar-fuel generation have been based on simple binary systems with limited success. However, ternary systems have not been explored extensively although they can offer more possibilities for band gap and band alignment tuning that allow the development of more efficient photoelectrochemical systems. Herein, we report on the growth of a novel ternary oxide photoanode material composed of self-ordered, vertically oriented nanotube arrays of titanium–molybdenum–nickel mixed oxide films via the anodization of a Ti–Mo–Ni alloy in an electrolyte solution of formamide containing NH₄F at room temperature, followed by annealing in an air atmosphere. The nanostructure topology was found to depend on both the anodization time and the applied voltage. Our results demonstrate the ability to grow mixed oxide nanotube array films that are several microns thick. The Ti–Mo–Ni mixed oxide nanotube array films were utilized in solar-spectrum water photoelectrolysis, demonstrating a photocurrent density of 2.1 mA cm⁻² and a ∼10 fold increase in the photoconversion efficiency under AM 1.5 illumination (100 mW cm⁻², 1 M KOH) compared to pure TiO₂ nanotubes fabricated under the same conditions. This enhancement in the photoconversion efficiency can be related to the synergistic effects of Ni and Mo alloying and the unique structural properties of the fabricated nanotube arrays.