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

Abstract

Black-TiO₂ has become increasingly interesting as a promising photoactive material. Most of the preparations for black-TiO₂ 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 TiO₂ electrode to black-TiO₂ at room temperature. A series of Mo–Ti oxo-clusters, [Ti₄Mo₄O₁₀(OR)₁₄(X-BA)₂] (BA = benzoate, X = H (1), F (2), Cl (3), and Br (4)), were prepared and were characterized by crystallography. They have a Mo₄Ti₄ structure with Mo(V)–Mo(V) metal–metal interactions. The activated hydrogen (H*) generated by electrochemically catalytic water splitting turns the TiO₂ electrode to black-TiO₂ at room temperature, due to the reduction of Ti(IV) to H⁺Ti(III). The potentials applied for water reduction must generally be higher than the overpotential at the TiO₂ 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-TiO₂ electrode, the effective electrochemical catalytic degradation of a dye was examined in comparison with the degradation using the white TiO₂ electrode. This work provides a method for the facile preparation of a black-TiO₂ film, and is a step forward in black-TiO₂ research.