Performance of Magnéli phase Ti4O7 and Ti3+ self-doped TiO2 as oxygen vacancy-rich titanium oxide anodes: Comparison in terms of treatment efficiency, anodic degradative pathways, and long-term stability

Abstract

This study compared hydrogen annealing and cathodic polarization (producing Magnéli phases and Ti3+ self-doped TiO2, respectively) as strategies to fabricate electrically conducting titanium oxides through oxygen non-stoichiometry creation for anodic water treatment. Electrochemical characterization techniques suggested that Ti4O7 best-suited for redox electrocatalysis among the Magnéli phases exhibited higher electrical conductivity than the self-doped TiO2. This aligned with the superiority of Ti4O7 over the self-doped TiO2 in chlorine evolution and anodic organic oxidation. Hydroxyl radical primarily contributed to anodic oxidation by two conductive titanium oxides at sulfate-based electrolyte, based on the retarding effects of radical scavengers, multi-activity assessment, electron paramagnetic resonance spectral features, and product distribution. Repetitive batch experiments and long-term tests in continuous operation mode demonstrated that self-doped TiO2 underwent more drastic performance reduction than Ti4O7. This accorded with the self-doped TiO2 being more vulnerable to activity loss, chemical alteration, and structural damage during prolonged application.