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

• Published in: Nano energy 2021-01, Vol.79, p.105483, Article 105483
• Main Authors: Park, Hong Ryeol, Pawar, Amol Uttam, Pal, Umapada, Zhang, Tierui, Kang, Young Soo
• Format: Article
• Language: English
• Subjects: CO2 activation; CO2 reduction mechanism; In-Situ XAFS/ATR-IR; oxygen vacancy; Photocatalytic CO2 reduction
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2020.105483

Intrinsic oxygen vacancies at CeO2 surface are known to activate thermodynamically stable CO2 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 CO2 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 CeO2 to form rGO-grafted NiO-CeO2 photocatalyst, which can convert CO2 to formaldehyde at a rate of 421.09 μmol g−1 h−1; about 4 times higher than that of pristine CeO2. Formation of photo-induced oxygen vacancy of CeO2 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 CO2 anion radical (CO2•-) and its subsequent protonation with in-situ electron paramagnetic resonance spectroscopy and attenuated total reflection-infrared (ATR-IR) spectroscopy, mechanism and reaction pathway of CO2 reduction into formaldehyde formation have been elucidated. Schematic representation of rGO grafted NiO-CeO2 nanocomposite and Photocatalytic CO2 reduction process with experimental CO2 reduction yield. [Display omitted] •A rGO-grafted NiO-CeO2 nanocomposite was fabricated through a simple hydrothermal process for ptotocatalytic CO2 reduction.•The hybrid nanocomposite reduces CO2 to formaldehyde liquid fuel under solar light irradiation.•The hybrid nanocomposite produces formaldehyde at four times higher (421.09 mmolg−1h−1) than pristine CeO2 nanostructures.•Formation of photoinduced oxygen vacancy at CeO2 surface and CO2•- radicals were monitored by in-situ XANES and in-situ EPR.•A step-by-step description of the multi-step CO2 photoreduction process has been provided.