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 degrees C, achieved in the transition metal oxides SrCoOx (ref. 1) and LuFe2O4+x (ref. 2) via thermal cycling. Here, we report rapid and reversible oxygen scavenging by TiO2-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 O-2 g(-1) min(-1), similar to 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 TiO2-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 anatase(6).