Synergy of the catalytic activation on Ni and the CeO ₂ -TiO ₂ /Ce ₂ Ti ₂ O ₇ stoichiometric redox cycle for dramatically enhanced solar fuel production

Solar thermochemical approaches to CO ₂ and H ₂ O splitting have emerged as an attractive pathway to solar fuel production. However, efficiently producing solar fuel with high redox kinetics and yields at lower temperature remains a major challenge. In this study, Ni promoted ceria-titanium oxide (CeO ₂ -TiO ₂ ) redox catalysts were developed for highly effective thermochemical CO ₂ and H ₂ O splitting as well as partial oxidation of CH ₄ at 900 °C. Unprecedented CO and H ₂ production rates and productivities of about 10-140 and 5-50 times higher than the current state-of-the-art solar thermochemical carbon dioxide splitting and water splitting processes were achieved with simultaneous close to complete CH ₄ conversions and high selectivities towards syngas. The underlying mechanism for the exceptional reaction performance was investigated by combined experimental characterization and density functional theory (DFT) calculations. It is revealed that the metallic Ni and the Ni/oxide interface manifest catalytic activity for both CH ₄ activation and CO ₂ or H ₂ O dissociation, whereas CeO ₂ -TiO ₂ enhances the lattice oxygen transport via the CeO ₂ -TiO ₂ /Ce ₂ Ti ₂ O ₇ stoichiometric redox cycle for CH ₄ partial oxidation and the subsequent CO ₂ or H ₂ O splitting promoted by catalytically active Ni. Such findings substantiate the significance of the synergy between the reactant activation by catalytic sites and the stoichiometric redox chemistry governing oxygen ion transport, paving the way for designing prospective materials for sustainable solar fuel production.