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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable 1 Overview—The Role of Bioinspired Chemistry in Improving Alternative Energy Technologies Understanding the basic processes of photosynthesis and chemical conversion may enable scientists to create systems that mimic biomolecules and produce energy more efficiently. Some of the losses in photovoltaic energy conversion might be overcome with biomimetic processes.1 Much work has been conducted in the development of artificial photosynthetic antennas, which provide rapid electron-transfer, as well as artificial reaction centers that generate a chemical potential by providing long-lived charged separation.2 As in photosynthesis, light energy can be harvested to drive a sequential reaction in which water is oxidized to hydrogen (for the hydrogen economy) and oxygen.3 Extensive progress has been made in catalyzing the formation of hydrogen from protons. Several catalysts have been developed to mimic hydrogenase activity.4,5 However, a rate limiting step in water oxidation that remains to be overcome is the stitching together of oxygen atoms to form O2 via bioinspired catalysts.6 In an effort to advance the understanding of “bioinspired chemistry for energy,” this workshop featured presentations, a poster session, and discussions on chemical issues by experts from government, industry, and academia (see Appendix A for workshop agenda). Speakers at the workshop Summarized the current energy challenges, such as carbon emissions, population growth, and cost, and presented opportunities to address these challenges, such as developing sustainable energy sources. Provided an overview of the fundamental aspects and robust implementations of bioinspired chemistry from government, academic, and industrial perspectives. Explored the role of fundamental chemistry in biocatalysis applications for energy systems. Addressed how improvements in bioinspired catalysis might be harnessed for improved energy systems. Discussed the most promising research developments in bioinspired chemistry for energy systems. Identified future research directions. WORKSHOP STRUCTURE The main speaker sessions are briefly described below. A more detailed summary of the speaker comments can be found in the chapters indicated in parentheses. The three main speaker sessions were: Government, industry, and academic perspectives on bioinspired chemistry for energy (Chapter 2). Fundamental aspects of bioinspired chemistry for energy (Chapter 3). Robust implementation of bioinspired catalysis (Chapter 4). In addition, two overarching themes were highlighted throughout the sessions: (1) partnership and integration (see 1 LaVan, D. A. and J. N. Cha. 2006. Approaches for Biological and Biomimetic Energy Conversion. Proceedings of the National Academy of Sciences 103(14): 5251-5255. 2 Gust, D., A. Moore, and T. Moore. 2001. Mimicking Photosynthetic Solar Energy Transduction. Accounts of Chemical Ressearch 34(1): 40-48. 3 Dismukes, C. 2001. Photosynthesis: Splitting Water. Science 292 (5516): 447-448. 4 Liu, T. and M. Darensbourg. 2007. A Mixed-Valent, Fe(II)Fe(I), Diiron Complex Reproduces the Unique Rotated State of the [FeFe] Hydrogenase Active Site. Journal of the American Chemical Society 129(22): 7008-7009. 5 Rauchfuss, T. 2007. Chemistry: A Promising Mimic of Hydrogenase Activity Science 316(5824): 553-554. 6 Service, R. F. 2007. Daniel Nocera Profile: Hydrogen Economy? Let Sunlight Do the Work Science 315(5813): 789.
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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable Chapter 5) and (2) research challenges, education, and training (see Chapter 6). Opening remarks were made by Douglas Ray, Pacific Northwest National Laboratory followed by an overview perspective given by John Turner, National Renewable Energy Laboratory. Next, government perspectives on bioinspired chemistry for energy were presented by Eric Rohlfing, Office of Basic Energy Sciences Department of Energy; Michael Clarke, Chemistry Division, National Science Foundation; Judy Raper, Division of Chemical, Bioengineering, Environmental, and Transport Systems National Science Foundation; and Peter Preusch, National Institute of General Medical Science, National Institutes of Health. The government perspectives were followed by industry perspectives on bioinspired chemistry for energy with presentations given by Henry Bryndza, DuPont; Brent Erickson, Biotechnology Industry Organization; and Magdalena Ramirez, British Petroleum. The overview session concluded with open discussion moderated by Sharon Haynie, DuPont. The first technical session covered fundamental aspects of bioinspired chemistry for energy, and included the following topics and speakers: Hydrogen-Processing Catalysts for Replacement of Platinum in Fuel Cell Electrodes: Hydrogenases, Marcetta Darensbourg, Texas A&M University; The Lesson from the Hydrogenases? New Chemistry (Happens to Be Strategic), Thomas Rauchfuss, University of Illinois at Urbana-Champaign; Self-Assembly of Artificial Photosynthetic Systems for Solar Energy Conversion, Michael Wasielewski, Northwestern University and Argonne National Laboratory; and Sustained Water Oxidation by Bioinspired Catalysts: The Real Thing Now, Charles Dismukes, Princeton University. The talks were followed by open discussion, moderated by Sharon Haynie. Speakers discussing fundamental aspects were asked to address the following questions: What are the design principles that enable biomolecular machines to effect selective and efficient atom- and group-transfer processes useful for energy conversions? What are the fundamental mechanisms of multielectron transfer in biological systems? What are the principles of energy storage and production in biology? How do biological systems such as catalysts composed of seemingly fragile peptide residues achieve durability and robustness? The technical session on fundamental aspects of bioinspired chemistry for energy concluded with remarks by Sharon Haynie, followed a poster session in which students and junior researchers presented emerging ideas in the realm of bioinspired chemistry for energy. Abstracts for the poster presenters are in Appendix C. The first day of the workshop adjourned after the poster session. Day two of the workshop opened with remarks by Leonard Buckley, Naval Research Laboratory, followed by the academic perspective on bioinspired chemistry, Solar Fuels: A Reaction Chemistry of Renewable Energy presented by Daniel Nocera, Massachusetts Institute of Technology. Next, there was a technical session on robust implementation of bioinspired catalysts, which included the following topics and speakers: Mimicking Photosynthetic Energy Transduction, Thomas Moore, Arizona State University; Biological Transformations for Energy Production: An Overview of Biofuel Cells, G. Tayhas Palmore, Brown University; and Bioinspired Initiatives at DuPont, Mark Emptage, DuPont. Open discussion was then moderated by Leonard Buckley. Speakers addressing robust implementation responded to the following questions: How can bioinspired design principles be replicated in synthetic and semisynthetic catalysts and catalytic processes? Can discovery methods (e.g., bioinformatics) be harnessed to encode designer catalytic sites? To what extent can protein scaffolds be replicated with more easily synthesized supports, and can we use these principles to design sequential catalytic assemblies? The workshop concluded with remarks by Leonard Buckley. OPENING REMARKS Douglas Ray of the Pacific Northwest National Laboratory welcomed about 75 workshop participants and provided some initial thoughts on the energy crisis and how chemistry can play a role. With about 86 percent of energy currently coming from coal, gas, and oil, and only 7 percent from renewables (mostly conventional hydroelectric and biomass; see Figure 1.1),7 Ray noted it is important to consider whether renewables, such as solar energy, hydrogen fuel, and biofuels, could reach the necessary scale needed to support current energy demand. He questioned whether our quality of life would be affected by the energy sources used. Ray also explained that progress in the energy field will depend on how scientists shape the future. He explained that transformational science—which focuses on translating what can be learned from biology to energy issues—is critical for changes to take place. Workshop Charge Ray then motivated the workshop participants to take advantage of this opportunity to reach across disciplines and learn from one another. He hoped that the workshop discussion would bring together traditional scientific disciplines to identify new science directions. Ray talked about what can be learned from biology and how that knowledge can be translated into more robust applications through chemistry. The forum was an opportunity to create new understanding and identify a research agenda for the future. Ray concluded 7 Energy Information Agency. 2007. Renewable Energy Annual, 2005 Edition. Table 1. http://www.eia.doe.gov/cneaf/solar.renewables/page/rea_data/rea_sum.html (accessed 11/16/07).
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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable FIGURE 1.1 The role of renewable energy consumption in the nation’s energy supply, 2005. SOURCE: Energy Information Agency. 2007. Renewable Energy Annual, 2005 Edition. Table 1. http://www.eia.doe.gov/cneaf/solar.renewables/page/rea_data/rea_sum.html (accessed 11/16/07). his presentation with the following questions to keep in mind during the workshop: How do we organize bioinspired systems to effectively manage charge transport, electron transfer, proton relays, and allow efficient interconversion of light and electrical charge? How are the properties of bioinspired systems affected when they are coupled with interfacial and nanoscale systems? How do we control the properties and architectures of biomolecular systems and materials? What role do weak interactions play in self-assembly of molecular and nanostructured materials? SETTING THE STAGE: OPPORTUNITIES AND CHALLENGES FOR ENERGY PRODUCTION John Turner of the National Renewable Energy Laboratory provided background information about energy to serve as a basis for the rest of the workshop discussions. “Energy is as important to modern society as food and water. Securing our energy future is critical for the viability of our society. Time is of the essence and money and energy are in short supply,” said Turner. He estimated that 73 million tons of hydrogen per year for light-duty vehicles (assuming 300 million vehicles, and 12,000 miles per year) and 27 million tons of hydrogen per year for air travel would be needed to meet the current energy demand in the United States. With world population growing at a fast pace, the demand for energy grows, especially in developing nations, noted Turner. He commented that the United States needs to be concerned about energy usage in developing nations. He mentioned a quote by C. R. Ramanathan, former Secretary, Ministry of Non-Conventional Energy Sources, Government of India: “Energy is the major input of overall social-economic development.” According to Turner, the United States will need to provide the energy-generating technologies developed in this country to the developing nations in order for their standard of living to increase. Historically, as the standard of living for a country increases, the population growth rate decreases, said Turner. Realizing that the current energy system is expected to last for only 200-250 years, Turner posed the question: “What energy-producing technologies can be envisioned that will last for millennia and can be implemented in developing countries?” He explained that renewable energy systems—including biomass, solar, wind, geothermal, nuclear (fusion), hydro, wave, and hydrogen—will meet these needs because of sustainability, resource availability, and energy payback criteria. Figure 1.2 shows the solar, wind, biomass, and geothermal energy resources available in the United States. Hydrogen Turner highlighted hydrogen because it plays a role in every fuel available and is a potential sustainable fuel on its own. He provided his own definition of a hydrogen economy: “The production of hydrogen, primarily from water but also from other feedstocks (mainly biomass), its distribution, and its utilization as an energy carrier.” Turner explained that the goal is to develop the hydrogen economy so that it can be used for transportation and energy storage and back up intermittent sustainable resources, such as solar and wind. Feedstocks, including water, fossil fuels, and biomass, can produce hydrogen through a number of pathways, including electrolysis, thermolysis, and conversion technologies. Biomass feedstocks can comprise crop residues, forest residues, energy crops, animal waste, and municipal waste, and, according to Turner, could have the potential to provide 15 percent of the world’s energy by 2050.8 Some challenges 8 Fischer, G. and L. Schrattenholzer, 2001. Global Bioenergy Potentials Through 2050. Biomass and Bioenergy 20: 151-159.
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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable FIGURE 1.2 Geographic distribution of U.S. sustainable energy resources: Solar, wind, biomass, and geothermal. SOURCE: Presented by John Turner, National Renewable Energy Laboratory. with this option include biomass availability, cost, and physical and chemical properties. Biomass can provide significant energy, but, said Turner, it is important to remember that its main role is to be a food source and it can also be an important chemical feedstock to replace fossil-based feedstocks. Turner then explained how electrolysis is a commercial process that produces hydrogen by splitting water using electricity. This commercial technology can generate hydrogen as an energy carrier using sustainable energy resources, such as wind and PV, which directly generate electricity. Turner warned of the challenges with some electrolysis technologies involving the use of platinum group metals, largely due to the high price of the these metals (about $1,300 an ounce or $46 a gram for platinum, according to Turner). Thermochemical water-splitting cycles handle chemicals and materials under conditions that challenge the current state of the art for construction materials and heat transfer fluids. For solar energy, such infrastructure needs also include solar reflectors and thermal storage. Turner does not think that thermochemical cycles should be a high priority because they are extremely challenging and these thermal-based systems are probably better used to produce electricity. Direct conversion systems use the energy of visible light to split water into hydrogen and oxygen. Combining light harvesting and water-splitting systems into a single system uses semiconductor, photoelectrolysis, and photobiological systems. According to Turner, the sustainable paths to hydrogen are: Solar energy → heat → thermolysis → hydrogen Solar energy → biomass → conversion → hydrogen Solar energy → electricity → electrolysis → hydrogen Solar energy → photolysis → hydrogen Growth Rates and Payback Turner emphasized the importance of growth rates for technology deployment and energy demand. New energy technologies can be a significant challenge but also a benefit, depending on the technology. Turner noted that the worldwide demand for energy continues to grow. Thus, alternative technologies must grow at high rates in to have an impact. The installation of wind farms, for example, is growing quickly; in fact, wind energy has a 27 percent average
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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable TABLE 1.1 Energy Payback Comparisons for PV and Wind Technology Lifetime Payback Payback ratio Solar: Crystalline and thin film photovoltaic cells (includes frames and supports) 30 years 2-3 years 10 Wind: fiberglass blade turbines (includes mechanical parts and scrapping the turbine at the end of its life) 20 years 3-4 months 20 SOURCE: Presentation by John Turner, National Renewable Energy Laboratory. growth rate in the United States, says Turner. Although wind currently supplies less than 1 percent of electricity, Turner suggested that its high growth rate would quickly increase its market share. If wind could maintain that 27 percent growth rate, Turner thinks that by 2020 the kilowatt hours from wind could surpass that generated from current U.S. nuclear power plants. In 2005, production of photovoltaics (PV) rose by 47 percent, which is indicative of world demand. If PV could maintain a growth rate of 30 percent, Turner said PV production would rise to 1 TW per year (peak) in 2028, but because of the steady increase in demand, this would only represent 10 percent of electricity needs. He pointed out that any technology that hopes to address carbon-free energy needs should be on the ground now and maintain close to a 30 percent growth rate for the next 20 years to have an impact. Because coal with carbon capture and storage will take years to get on ground, it may be too late to make a significant contribution to future carbon-free energy systems. “If we want a change in the energy infrastructure in the next 50 years or so, we have to start and maintain these large growth rates in alternative energy technologies,” said Turner. He stated that energy payback—a net gain in energy—is another important consideration when choosing the best energy resource. Turner believes that any system without net energy payback will eventually be replaced by another energy system. Positive net energy occurs only with energy systems that are converting energy from outside the biosphere, said Turner—such as for solar (PV) and wind (see Table 1.1). However, he added that for PV, growth rates above 35 percent require a large energy input (e.g., to produce the technology), and this leads to an overall negative energy balance (net loss of energy). Turner noted that wind is better in this respect, because it still provides an energy payback even at a 40 percent growth rate. Cost Fuel costs for transportation was another issue raised in Turner’s presentation. In the United States, gasoline is currently about $3/gallon, which is 12¢/mile for a 25-mile-per-gallon vehicle. A National Renewable Energy Laboratory study has shown that at today’s costs a large wind farm coupled to a large electrolyzer plant can produce hydrogen at a cost of about $6/kg at the plant gate. If that hydrogen is used in a fuel-cell vehicle with a fuel economy of 50 miles per kilogram, that hydrogen as a transportation fuel is also 12¢/mi. Therefore, concluded Turner, hydrogen is on par with gasoline, and it should not cost much more to implement it on a larger scale. He also made a note of future water issues that may need to be addressed if hydrogen from water electrolysis is used more frequently. One hundred billion gallons of water per year will be required for the U.S. hydrogen-fuel-cell vehicle fleet. On the other hand, wind and PV consume no water during electricity production, and thermoelectric power generation utilizes only about 0.5 gallon of water for every kilowatt-hour produced. If wind and solar are aggressively installed, overall water use will decrease, said Turner.9 Vision for the Future Turner compared renewable energy and coal with carbon sequestration and explained that he prefers a renewable energy source because coal resources are finite and it takes energy to sequester carbon. To modify or build a new energy infrastructure requires money and energy—and that energy must come from existing resources. Turner’s vision for the pathway to the future includes promotion of renewable energy, developing fuel cells for transportation (hydrogen initially from natural gas), implementing large-scale electrolysis for hydrogen production as sustainable electricity increases, and increasing funding for electrocatalysis. He concluded with: “We have a finite amount of time, a finite amount of money, and a finite amount of energy, and we need to be very careful about the choices we make as we build any new energy infrastructure. I’d like to see something that will last for millennia, and certainly solar, wind, and biomass will last as long as the sun shines.” DISCUSSION Following Turner’s presentation, some workshop participants provided their own thoughts and asked questions of the speaker. Daniel Nocera followed up on Turner’s comments about energy scale. Nocera said that if a new material or new bioinspired approach can be done cheaply, there will not be the growth rate penalty for PV (above a 35 percent 9 For more information, see the recent NRC workshop summary on “Water Implications for Biofuels Production.” Soon to be released at www.nap.edu.
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Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable growth rate) that Turner mentioned earlier. Scientists can create new technologies to improve the energy payback, according to Nocera. Turner agreed, and said that scientists need to find less energy-intensive ways to make energy conversion systems, while also maintaining the growth rate. The quicker that more efficient, less expensive materials and systems are identified, the easier society can move to a sustainable energy system. Frankie Wood-Black of ConocoPhillips mentioned that there can be unintended consequences of new energy systems and that scientists will need to consider these potential unintended consequences when new technologies are being developed. She used hydrogen and electric cars as an example. Since those vehicles are much quieter than vehicles with traditional combustion engines, pedestrians do not hear them and are at risk of being involved in an accident. Charles Casey of the University of Wisconsin brought up concerns about hydrogen as an energy carrier because of infrastructure challenges. He suggested that hydrogen be converted into hydrocarbons since the infrastructure is already available for hydrocarbons. Turner responded by stating that the infrastructure really does not exist for synthesis of these proposed hydrocarbons. Carbon dioxide would have to be taken out of the air and added to hydrogen in order to generate a fuel, which is a huge challenge in the United States, said Turner. He argued that a hydrogen infrastructure does indeed exist since 9 million tons of hydrogen is produced every year in the United States. The hydrogen infrastructure is just not in a form that is recognized.