Enhanced solar photoreduction of CO2 to liquid fuel over rGO grafted NiO-CeO2 heterostructure nanocomposite

Intrinsic oxygen vacancies at CeO 2 surface are known to activate thermodynamically stable CO 2 molecules, enhancing the reaction rate and reducing reduction energy. However, charge recombination at the ceria-based cathode surface suppresses the multi-electron transfer process required for a complete reduction of CO 2 molecules to generate useful hydrocarbons. To suppress this charge recombination and facilitate the multi-electron transfer process, p-type NiO and reduced graphene oxide (rGO) were hybridized with CeO 2 to form rGO-grafted NiO-CeO 2 photocatalyst, which can convert CO 2 to formaldehyde at a rate of 421.09 μmol g −1 h −1 ; about 4 times higher than that of pristine CeO 2 . Formation of photo-induced oxygen vacancy of CeO 2 photocatalyst resulted in a change of Ce-O bond length at ceria surface were monitored in-situ by X-ray absorption near edge structure (XANES), and X-ray absorption fine structure (EXAFS) spectroscopy. Tracking the formation of CO 2 anion radical (CO 2 •- ) and its subsequent protonation with in-situ electron paramagnetic resonance spectroscopy and attenuated total reflection-infrared (ATR-IR) spectroscopy, mechanism and reaction pathway of CO 2 reduction into formaldehyde formation have been elucidated. Schematic representation of rGO grafted NiO-CeO 2 nanocomposite and Photocatalytic CO 2 reduction process with experimental CO 2 reduction yield. • A rGO-grafted NiO-CeO 2 nanocomposite was fabricated through a simple hydrothermal process for ptotocatalytic CO 2 reduction. • The hybrid nanocomposite reduces CO 2 to formaldehyde liquid fuel under solar light irradiation. • The hybrid nanocomposite produces formaldehyde at four times higher (421.09 mmolg −1 h −1 ) than pristine CeO 2 nanostructures. • Formation of photoinduced oxygen vacancy at CeO 2 surface and CO 2 •- radicals were monitored by in-situ XANES and in-situ EPR. • A step-by-step description of the multi-step CO 2 photoreduction process has been provided.