Graphene Oxides and Their Hybrids for CO2 Conversion and Solar Fuels

Finding effective ways for conversion of CO₂ into hydrocarbons (as energy fuels or chemical feedstock) is highly desirable to achieve sustainable development. Photocatalytic conversion of CO₂ to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO₂ reduction, two birds with one stone for the energy and environmental issues. In this talk, I will present our progress in using graphene oxides (GOs), along with their hybrids, as promising photocatalysts for CO₂ reduction.

Modified Hummer's method has been applied to synthesize the GOs with tunable band gap. Under visible light, the photocatalytic CO₂ to methanol conversion rate on our modified GOs is 0.172 μmol g-cat⁻¹ h⁻¹, which is six-fold higher than the popularly studied TiO₂ [Nanoscale 5 (2013) 262]. Meanwhile, a novel one-step and effective electrochemical (EC) method is developed to directly exfoliate graphite into thin reduced graphene oxide (RGO) nanosheets at room temperature. The oxidation degree of the RGOs, hence the C/O ratio, depends on the switching potentials of the EC synthesis. The ability to control the light-absorption of the RGOs by simply adjusting the switching potentials can be further achieved. This approach presents us a possibility for the environmentally friendly, ultrafast, low-cost, and large-scale production of RGOs and great potential in solar-fuel applications.

To enhance carrier generation and separation, therefore the resultant photocatalysis reaction, Cu and MoS₂ nanoparticles were further deposited on GOs as co-catalysts. Not only methanol, but also acetaldehyde was detected. Total solar to fuel yield of 6.8 μmole g-cat^-1 h^-1 has been achieved, which is 170 times enhancement relative to the commercial P-25 photocatalyst [Nano Lett. 14 (2014) 6097]. In all the above-mentioned hybrids, the photo-catalytic performance is always superior to that of constituent component when used alone. Detailed preparation and characterization of the catalysts will be presented. The role and interplay of the constituent components will also be discussed.