Molybdenum-titanium oxo-cluster, an efficient electrochemical catalyst for the facile preparation of black titanium dioxide film.

Black-TiO has become increasingly interesting as a promising photoactive material. Most of the preparations for black-TiO involve either high temperature calcination, plasma, lengthy chemical reactions or dealing with dangerous or toxic chemicals. We found, by accident, that Mo-Ti oxo-clusters are efficient catalysts for the hydrogenation of a TiO electrode to black-TiO at room temperature. A series of Mo-Ti oxo-clusters, [TiMoO(OR)(X-BA)] (BA = benzoate, X = H (1), F (2), Cl (3), and Br (4)), were prepared and were characterized by crystallography. They have a MoTi structure with Mo(v)-Mo(v) metal-metal interactions. The activated hydrogen (H*) generated by electrochemically catalytic water splitting turns the TiO electrode to black-TiO at room temperature, due to the reduction of Ti(iv) to HTi(iii). The potentials applied for water reduction must generally be higher than the overpotential at the TiO electrode (-1.0 V vs. RHE). In this work, the onset potential of hydrogen evolution significantly decreased to -0.1 V vs. RHE. Using this blackened 1-TiO electrode, the effective electrochemical catalytic degradation of a dye was examined in comparison with the degradation using the white TiO electrode. This work provides a method for the facile preparation of a black-TiO film, and is a step forward in black-TiO research.