CAREER: Integrated CO2 Capture and Catalytic Conversion to Solar Fuels Using Hybrid Multifunctional Materials

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ABSTRACTTechnical/Scientific MeritPhotocatalytic reduction of carbon dioxide (CO2) with water by sunlight is a highly desirable process to produce solar fuels such as methane and methanol. This technology not only reduces greenhouse gases (e.g., CO2) but also provides pathways to sustainable energy. However, CO2 activation and conversion is very challenging because of its stable thermodynamic properties. Despite increasing efforts in this area in recent years, the efficiency of photocatalytic CO2 reduction remains low. Some investigators believe important problems have yet to receive adequate exploration, including the nature of the photocatalyst surface active sites, its capacity for CO2 adsorption, the kinetics of reaction product desorption, and the long-term stability of the catalyst. In this NSF Faculty Early Career Development (CAREER) Program Award, Prof. Ying Li of the University of Wisconsin-Milwaukee will address a number of these issues. Li will explore a new concept of integrated CO2 capture and catalytic conversion (IC4) to produce solar fuels using novel multifunctional materials, with the aim to achieve significantly improved, stable CO2 conversion efficiency. The proposed multifunctional materials will exploit interacting adsorbent/catalyst components in the form of mixed metal oxides, layered double hydroxides (LDHs), and their hybrids, which are metal oxide nanoparticles embedded on reconstructed LDHs. Different morphologies and nanostructures of the adsorbent/catalyst components will be investigated to maximize the synergy between the two components/functions. Another unique idea in the proposed research is to perform the photocatalytic CO2 reaction at elevated temperatures in the range of 100 to 200 °C; whereas, conventional photocatalytic reactions are conducted at room or near-room temperatures. At these higher temperatures, the desorption of reaction intermediates and products from the catalyst surface will be enhanced, while the adsorbent component of the hybrid material will function to ensure CO2 adsorption. This slightly elevated temperature can be achieved by utilizing industrial waste heat or the infrared portion of sunlight in large-scale applications, and thus a higher overall solar energy conversion efficiency is expected. This CAREER project will also advance fundamental understanding of the CO2 photoreduction mechanism. CO2 adsorption/desorption and the measured photocatalytic conversion efficiency will be correlated with comprehensive material characterization, through advanced spectroscopic methods including in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and x-ray absorption spectroscopy (XAS). These combined approaches will be powerful tools to investigate changes in material properties during photoreaction, interactions of adsorbates on the surface, fate of reaction intermediates, charge transfer pathways, and factors that affect catalyst activity and stability. Broader ImpactThe results of this proposed research in converting greenhouse gases like CO2 to fuels will have significant impact on the development of sustainable energy technology. The current research on CO2 capture and CO2 conversion/utilization are separately investigated in the scientific community. The proposed concept of integrated CO2 capture and catalytic conversion at slightly elevated temperatures using hybrid adsorbent/catalyst materials offers a new route to solve this very challenging problem in a more integrated, efficient way. The new material design and fundamental understanding in catalyst stability in this research by Prof. Li will also shed light on other photocatalytic systems such as solar hydrogen production from water splitting.As expected for CAREER projects, the proposed research will be integrated into teaching and curriculum development. Graduate students will be trained in this interdisciplinary research; undergraduate and high school students, particularly those in underrepresented groups, will be recruited to participate in the research project. Outreach programs are planned in collaboration with Milwaukee Public Schools and non-profit education organizations in Milwaukee urban areas such as the Urban Ecology Center, to assist teachers to build course materials related to solar energy and nanotechnology, thereby increasing the students? awareness in global climate change while promoting interests in the STEM fields.