Reversible oxygen scavenging at room temperature using electrochemically reduced titanium oxide nanotubes

A material capable of rapid, reversible molecular oxygen uptake at room temperature is desirable for gas separation and sensing^1,2, for technologies that require oxygen storage and oxygen splitting such as fuel cells (solid-oxide fuel cells in particular)^3-6 and for catalytic applications that require reduced oxygen species (such as removal of organic pollutants in water and oil-spill remediation). To date, however, the lowest reported temperature for a reversible oxygen uptake material is in the range of 200-300 °C, achieved in the transition metal oxides SrCoO_x (ref. 1) and LuFe₂O_4+x (ref. 2) via thermal cycling. Here, we report rapid and reversible oxygen scavenging by TiO_2-x nanotubes at room temperature. The uptake and release of oxygen is accomplished by an electrochemical rather than a standard thermal approach^1,2,7. We measure an oxygen uptake rate as high as 14 mmol O₂ g^-1 min^-1, ∼2,400 times greater than commercial, irreversible oxygen scavengers. Such a fast oxygen uptake at a remarkably low temperature suggests a non-typical mechanistic pathway for the re-oxidation of TiO_2-x. Modelling the diffusion of oxygen, we show that a likely pathway involves 'exceptionally mobile' interstitial oxygen^8-10 produced by the oxygen adsorption and decomposition dynamics, recently observed on the surface of anatase⁶.