Atmospheric CO2 capture and photofixation to near-unity CO by Ti3+-Vo-Ti3+ sites confined in TiO2 ultrathin layers

To realize efficient atmospheric CO2 chemisorption and activation, abundant Ti3+ sites and oxygen vacancies in TiO2 ultrathin layers were designed. Positron annihilation lifetime spectroscopy and theoretical calculations first unveil each oxygen vacancy is associated with the formation of two Ti3+ sites, giving a Ti3+-Vo-Ti3+ configuration. The Ti3+-Vo-Ti3+ sites could bond with CO2 molecules to form a stable configuration, which converted the endoergic chemisorption step to an exoergic process, verified by in-situ Fourier-transform infrared spectra and theoretical calculations. Also, the adjacent Ti3+ sites not only favor CO2 activation into COOH* via forming a stable Ti3+-C-O-Ti3+ configuration, but also facilitate the rate-limiting COOH* scission to CO* by reducing the energy barrier from 0.75 to 0.45 eV. Thus, the Ti3+-Vo-TiO2 ultrathinlayers could directly capture and photofix atmospheric CO2 into near-unity CO, with the corresponding CO2-to-CO conversion ratio of ca. 20.2%.