Enhanced Electrocatalytic Oxygen Reduction Reaction of TiO 2 Nanotubes by Combining Surface Oxygen Vacancy Engineering and Zr Doping.

This work examines the cooperative effect between Zr doping and oxygen vacancy engineering in anodized TiO 2 nanotubes (TNTs) for enhanced oxygen reduction reactions (ORRs). Zr dopant and annealing conditions significantly affected the electrocatalytic characteristics of grown TNTs. Zr doping results in Zr 4+ substituted for Ti 4+ species, which indirectly creates oxygen vacancy donors that enhance charge transfer kinetics and reduce carrier recombination in TNT bulk. Moreover, oxygen vacancies promote the creation of unsaturated Ti 3+ (Zr 3+ ) sites at the surface, which also boosts the ORR interfacial process. Annealing at reductive atmospheres (e.g., H 2 , vacuum) resulted in a larger increase in oxygen vacancies, which greatly enhanced the ORR activity. In comparison to bare TNTs, Zr doping and vacuum treatment (Zr:TNT-Vac) significantly improved the conductivity and activity of ORRs in alkaline media. The finding also provides selective hydrogen peroxide production by the electrochemical reduction of oxygen.