Synergy of the catalytic activation on Ni and the CeO2–TiO2/Ce2Ti2O7 stoichiometric redox cycle for dramatically enhanced solar fuel production

Abstract

Solar thermochemical approaches to CO₂ and H₂O 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 (CeO₂–TiO₂) redox catalysts were developed for highly effective thermochemical CO₂ and H₂O splitting as well as partial oxidation of CH₄ at 900 °C. Unprecedented CO and H₂ 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 CH₄ 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 CH₄ activation and CO₂ or H₂O dissociation, whereas CeO₂–TiO₂ enhances the lattice oxygen transport via the CeO₂–TiO₂/Ce₂Ti₂O₇ stoichiometric redox cycle for CH₄ partial oxidation and the subsequent CO₂ or H₂O 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.