Energy will be the Next Scientific Grand Challenge.
The past two decades have witnessed a dramatic increase in global energy consumption. While this need has been largely met by fossil fuels, the rapidly increasing global competition for this limited resource and the expectation that the Earth’s energy needs will double by 2050 and triple by the end of the century, has generated growing concern over future availability.
Combine the above with the mounting evidence that carbon dioxide emissions are adversely affecting global climate, and it becomes increasingly clear that developing renewable carbon-neutral energy sources constitutes a grand challenge for the scientific community.
The sun provides about 10,000 times our current daily energy needs and is the ultimate solution to the world's need for renewable, environmentally friendly energy. However, to be practical, utilization of solar energy requires energy storage on massive scales, far greater than any existing technology. Photosynthesis provides a role model in this regard, with the only practical approach consisting of an "Artifical Photosynthesis" strategy with "solar fuels" as the product. Solar fuels are high-energy molecules like carbohydrates or hydrogen with the energy of the sun stored in chemical bonds. Target reactions are water splitting into hydrogen and oxygen and light-driven reduction of CO2 to CO or other reduced forms of carbon.
At the U.S. DOE-funded Energy Frontier Research Center at the University of North Carolina at Chapel Hill, our goal is to generate solar fuels using dye-sensitized photoelectrosynthesis cells (DSPEC). Molecules do most of the work in this approach, absorbing light, transferring electrons, and catalyzing reactions. The DSPEC design also benefits from a modular approach, allowing the separate parts to be synthesized, evaluated, and improved in an iterative manner. Using an integrated team-based structure, we are making real progress in translating our concept of the DSPEC into a viable prototype. Many challenges lie ahead but there is light shining at the end of a very long tunnel.
To address the challenges in creating a sustainable energy future, the UNC EFRC: Center for Solar Fuels, funded by the US Department of Energy, Office of Basic Energy Sciences, was established in 2009 at one of the top five public research universities in the United States, the University of North Carolina at Chapel Hill.
Led by a distinguished faculty, including members of the National Academy of Sciences, UNC EFRC leverages key discoveries made at UNC during the past 20 years and collaborations with other research institutions to assemble a critical mass of scientists working together on energy-related research. The research center is headquartered at UNC-CH in partnership with Duke University, North Carolina Central University, the University of Florida, Research Triangle Institute, Georgia Institute of Technology and the University of Colorado at Boulder.
The UNC EFRC is conducting research on capturing sunlight to drive solar fuel reactions. The Center's efforts range from basic research on fundamental processes to integrating components into sub-systems and sub-systems into prototypical devices. The research utilizes a broad, multidisciplinary approach in a highly collaborative setting drawing on expertise across a broad range of disciplines in chemistry, physics, and materials sciences. The primary target is a Dye Sensitized Photoelectrosynthesis Cells (DSPEC) for solar fuels production as illustrated below.
Multiple platforms are under investigation but the primary focus is on Dye Sensitized Photoelectrosynthesis Cells (DSPEC). This approach utilizes molecules and molecular assemblies for catalysis in photoelectrochemical configurations closely related to those used in Dye Sensitized Solar Cells (DSSC). The Figure shows a schematic diagram for a DSPEC for light driven water reduction of CO2 to methane. In contrast to a DSSC, where the target is creating a photopotential and photocurrent, the target of a DSPEC is production of a high energy fuel with oxygen as the co-product in the physically separated compartments of a photoelectrochemical cell. The UNC EFRC approach is distinctive based on the design and utilization of separate functional modules, maximizing their performance, and integrating them into device prototypes featuring both single and tandem photoelectrode configurations.
Multiple themes have been developed in parallel — light absorption, excited state electron and energy transfer, electron and proton transfer driven by free energy gradients, and catalysis of water oxidation and water/CO2 reduction — with integration in photoelectrochemical cell configurations. In the modular approach the separate components are designed and tested for maximum performance and then integrated into the final DSPEC architecture. DSPEC research benefits from, and is enriched by, parallel research in electrocatalysis and Dye Sensitized Solar Cells.
Hallmarks of Center research are: (1) fundamental studies on reaction mechanisms, (2) synthesis of novel materials combining light absorption and catalysis, (3) preparation and characterization of designed photocatalytic interfaces, (4) application of theory and experiment to provide guiding principles for component design, integrated systems, and devices, and (5) augmentation of research findings and multidisciplinary strengths in research collaborations with national laboratories, other EFRCs, and the Research Triangle Solar Fuels Institute. The latter has been a key partner, extending the research findings of the EFRC through the translation stage to device prototypes.
The Center employs an integrated, interdisciplinary team-based approach to research in Solar Fuels based on four research areas, Catalysis, Assemblies, Interfacial Synthesis and Characterization, Device Prototypes. Eight research teams, led by faculty members at UNC and partner institutions, pursue research in these areas with the theory effort fully integrated into the experimental teams.
Water Oxidation Team:
Development of new solution and interfacial catalysts for water oxidation.
CO2 Reduction Team:
Development of new solution and interfacial catalysts for CO2 reduction.
Synthesis and characterization of molecular assemblies based on polymer scaffolds for multi-chromophore applications.
Molecular assemblies based on peptide scaffolds for control of chromophore/catalyst geometry.
Framework Materials Team:
Organic-inorganic hybrid materials for integrated light-harvesting and catalysis.
Interface Synthesis Team:
Synthesis and attachment of chromophore-catalyst assemblies at metal oxide interfaces.
Interface Characterization Team:
Characterization of interfacial structure and dynamics by transient and surface spectroscopies.
DSPEC Devices Team:
Evaluation and performance of integrated catalysts, assemblies and new transparent metal oxide semiconductors in device prototype configurations.
To provide the basic research to enable a revolution in the collection and conversion of sunlight into storable solar fuels.
We will combine the best features of academic and translational research to study light/matter interactions and chemical processes for the efficient collection, transfer, and conversion of solar energy into chemical fuels.
Arey Distinguished Professor of Chemistry Thomas Meyer has been awarded the 2012 Porter Medal. This distinction is awarded every two years to the scientist who, in the opinion of the European Photochemistry Association, the Inter-American Photochemistry Society, and the Asian and Oceanian Photochemistry Association, has contributed most to the science of photochemistry with particular emphasis on more physical aspects, reflecting George Porter's own interests.