The Thermal-Oxidation Behavior of Pristine and Doped Magnéli Phase Titanium Oxides

Magnéli phase titanium oxides (Ti n O2n–1, 4 ≤ n ≤ 10) are promising alternatives to carbon-based materials in aqueous electrochemical technologies, but their passivation during operation remains an important challenge to address. To elucidate the mechanism for their oxidation and investigate the influence of doping on their oxidation stability, the thermal-oxidation behavior in air of Ti4O7 doped with V, Cr, Fe, and Ga was investigated by thermogravimetric analysis. V-doping and Fe-doping improved the thermal stability of Ti4O7 as evidenced by higher onset temperatures in their thermograms. Three-dimensional diffusion reaction models adequately describe the solid-state kinetics of thermal oxidation of Ti4O7 in air as demonstrated by linear model-fitting. Doping shows a mixed influence on the kinetics for thermal oxidation in air reducing both the Arrhenius pre-exponential factor and the activation energy. Cr-doping significantly shortens the lifetime of Ti4O7 in ambient conditions as determined by kinetic predictions.