Bioinspired Chemistry for Energy: A Workshop Summary to the Chemical Sciences Roundtable (2008)

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1 Overview—The Role of Bioinspired Chemistry in Improving Alternative Energy Technologies Understanding the basic processes of photosynthesis from government, industry, and academia (see Appendix A and chemical conversion may enable scientists to create for workshop agenda). Speakers at the workshop systems that mimic biomolecules and produce energy more efficiently. Some of the losses in photovoltaic energy conver- • Summarized the current energy challenges, such as sion might be overcome with biomimetic processes. Much carbon emissions, population growth, and cost, and presented work has been conducted in the development of artificial opportunities to address these challenges, such as developing photosynthetic antennas, which provide rapid electron- sustainable energy sources. transfer, as well as artificial reaction centers that generate a • Provided an overview of the fundamental aspects chemical potential by providing long-lived charged separa- and robust implementations of bioinspired chemistry from tion. As in photosynthesis, light energy can be harvested government, academic, and industrial perspectives. to drive a sequential reaction in which water is oxidized • Explored the role of fundamental chemistry in bio- to hydrogen (for the hydrogen economy) and oxygen. catalysis applications for energy systems. Extensive progress has been made in catalyzing the forma- • Addressed how improvements in bioinspired tion of hydrogen from protons. Several catalysts have been c ­ atalysis might be harnessed for improved energy systems. developed to mimic hydrogenase activity., However, a rate • Discussed the most promising research develop- limiting step in water oxidation that remains to be overcome ments in bioinspired chemistry for energy systems. is the stitching together of oxygen atoms to form O2 via • Identified future research directions. bioinspired catalysts. In an effort to advance the understanding of “bioinspired Workshop Structure chemistry for energy,” this workshop featured presentations, a poster session, and discussions on chemical issues by experts 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  LaVan, D. A. and J. N. Cha. 2006. Approaches for Biological and B ­ iomimetic Energy Conversion. Proceedings of the National Academy of main speaker sessions were: Sciences 103(14): 5251-5255.  Gust, D., A. Moore, and T. Moore. 2001. Mimicking Photosynthetic So- 1. Government, industry, and academic perspectives lar Energy Transduction. Accounts of Chemical Ressearch 34(1): 40-48. on bioinspired chemistry for energy (Chapter 2).  Dismukes, C. 2001. Photosynthesis: Splitting Water. Science 292 (5516): 2. Fundamental aspects of bioinspired chemistry for 447-448.  Liu, T. and M. Darensbourg. 2007. A Mixed-Valent, Fe(II)Fe(I), Diiron energy (Chapter 3). Complex Reproduces the Unique Rotated State of the [FeFe] ­Hydrogenase 3. Robust implementation of bioinspired catalysis Active Site. Journal of the American Chemical Society 129(22): 7008-7009. (Chapter 4).  Rauchfuss, T. 2007. Chemistry: A Promising Mimic of Hydrogenase Activity Science 316(5824): 553-554. In addition, two overarching themes were highlighted  Service, R. F. 2007. Daniel Nocera Profile: Hydrogen Economy? Let Sunlight Do the Work Science 315(5813): 789. throughout the sessions: (1) partnership and integration (see  

 BIOINSPIRED CHEMISTRY FOR ENERGY Chapter 5) and (2) research challenges, education, and train- Next, there was a technical session on robust imple- ing (see Chapter 6). mentation of bioinspired catalysts, which included the Opening remarks were made by Douglas Ray, Pacific following topics and speakers: Mimicking Photosynthetic Northwest National Laboratory followed by an overview Energy Transduction, Thomas Moore, Arizona State Uni- perspective given by John Turner, National Renewable versity; Biological Transformations for Energy Production: Energy Laboratory. Next, government perspectives on An Overview of Biofuel Cells, G. Tayhas Palmore, Brown bioinspired chemistry for energy were presented by Eric University; and Bioinspired Initiatives at DuPont, Mark Rohlfing, Office of Basic Energy Sciences Department of Emptage, DuPont. Open discussion was then moderated by Energy; Michael Clarke, Chemistry Division, National Leonard Buckley. Science Foundation; Judy Raper, Division of Chemical, Bio­ Speakers addressing robust implementation responded engineering, Environmental, and Transport Systems National to the following questions: How can bioinspired design prin- Science Foundation; and Peter Preusch, National Institute ciples be replicated in synthetic and semisynthetic catalysts of General Medical Science, National Institutes of Health. and catalytic processes? Can discovery methods (e.g., bio- The government perspectives were followed by industry informatics) be harnessed to encode designer catalytic sites? perspectives on bioinspired chemistry for energy with presen- To what extent can protein scaffolds be replicated with more tations given by Henry Bryndza, DuPont; Brent ­Erickson, easily synthesized supports, and can we use these principles Biotechnology Industry Organization; and ­ Magdalena to design sequential catalytic assemblies? Ramirez, British Petroleum. The overview session con- The workshop concluded with remarks by Leonard cluded with open discussion moderated by Sharon Haynie, Buckley. DuPont. The first technical session covered fundamental aspects Opening Remarks of bioinspired chemistry for energy, and included the fol- lowing topics and speakers: Hydrogen-Processing ­Catalysts Douglas Ray of the Pacific Northwest National Labora- for Replacement of Platinum in Fuel Cell Electrodes: tory welcomed about 75 workshop participants and provided ­ ydrogenases, Marcetta Darensbourg, Texas A&M Uni- H some initial thoughts on the energy crisis and how chemistry versity; The Lesson from the Hydrogenases? New Chemistry can play a role. With about 86 percent of energy currently (Happens to Be Strategic), Thomas Rauchfuss, University coming from coal, gas, and oil, and only 7 percent from of Illinois at Urbana-Champaign; Self-Assembly of Arti- renewables (mostly conventional hydroelectric and bio- ficial Photosynthetic Systems for Solar Energy Conver- mass; see Figure 1.1), Ray noted it is important to consider sion, Michael Wasielewski, Northwestern University and whether renewables, such as solar energy, hydrogen fuel, and Argonne National Laboratory; and Sustained Water Oxida- biofuels, could reach the necessary scale needed to support tion by Bioinspired Catalysts: The Real Thing Now, Charles current energy demand. He questioned whether our quality Dismukes, Princeton University. The talks were followed by of life would be affected by the energy sources used. Ray open discussion, moderated by Sharon Haynie. also explained that progress in the energy field will depend Speakers discussing fundamental aspects were asked to on how scientists shape the future. He explained that trans- address the following questions: What are the design princi- formational science—which focuses on translating what ples that enable biomolecular machines to effect selective and can be learned from biology to energy issues—is critical for efficient atom- and group-transfer processes useful for energy changes to take place. conversions? What are the fundamental mechanisms of multi- electron transfer in biological systems? What are the principles Workshop Charge of energy storage and production in biology? How do biologi- cal systems such as catalysts composed of seemingly fragile Ray then motivated the workshop participants to take peptide residues achieve durability and robustness? advantage of this opportunity to reach across disciplines and The technical session on fundamental aspects of bio- learn from one another. He hoped that the workshop discus- inspired chemistry for energy concluded with remarks by sion would bring together traditional scientific disciplines Sharon Haynie, followed a poster session in which students to identify new science directions. Ray talked about what and junior researchers presented emerging ideas in the realm can be learned from biology and how that knowledge can be of bioinspired chemistry for energy. Abstracts for the poster translated into more robust applications through chemistry. presenters are in Appendix C. The first day of the workshop The forum was an opportunity to create new understanding adjourned after the poster session. and identify a research agenda for the future. Ray concluded Day two of the workshop opened with remarks by L ­ eonard Buckley, Naval Research Laboratory, followed by the academic perspective on bioinspired chemistry, Solar Fuels: A Reaction Chemistry of Renewable Energy presented  Energy Information Agency. 2007. Renewable Energy Annual, 2005 Edition. Table 1. http://www.eia.doe.gov/cneaf/solar.renewables/page/ by Daniel Nocera, Massachusetts Institute of Technology. rea_data/rea_sum.html (accessed 11/16/07). 

OVERVIEW—THE ROLE OF BIOINSPIRED CHEMISTRY IN IMPROVING ALTERNATIVE ENERGY TECHNOLOGIES  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.renew- ables/page/rea_data/rea_sum.html (accessed 11/16/07). 1-1.eps low-res bitmap image his presentation with the following questions to keep in mind States will need to provide the energy-generating technolo- during the workshop: gies developed in this country to the developing nations in order for their standard of living to increase. Historically, as • How do we organize bioinspired systems to effec- the standard of living for a country increases, the population tively manage charge transport, electron transfer, proton growth rate decreases, said Turner. relays, and allow efficient interconversion of light and elec- Realizing that the current energy system is expected trical charge? to last for only 200-250 years, Turner posed the question: • How are the properties of bioinspired systems “What energy-producing technologies can be envisioned that affected when they are coupled with interfacial and nanoscale will last for millennia and can be implemented in developing systems? countries?” He explained that renewable energy systems— • How do we control the properties and architectures including biomass, solar, wind, geothermal, nuclear (fusion), of biomolecular systems and materials? hydro, wave, and hydrogen—will meet these needs because • What role do weak interactions play in self-­assembly of sustainability, resource availability, and energy payback of molecular and nanostructured materials? criteria. Figure 1.2 shows the solar, wind, biomass, and geo- thermal energy resources available in the United States. Setting the Stage: Opportunities and Challenges for Energy Production Hydrogen John Turner of the National Renewable Energy Labora- Turner highlighted hydrogen because it plays a role in tory provided background information about energy to serve every fuel available and is a potential sustainable fuel on its as a basis for the rest of the workshop discussions. “Energy is own. He provided his own definition of a hydrogen economy: as important to modern society as food and water. Securing “The production of hydrogen, primarily from water but also our energy future is critical for the viability of our society. from other feedstocks (mainly biomass), its distribution, and Time is of the essence and money and energy are in short its utilization as an energy carrier.” Turner explained that supply,” said Turner. He estimated that 73 million tons of the goal is to develop the hydrogen economy so that it can hydrogen per year for light-duty vehicles (assuming 300 be used for transportation and energy storage and back up million vehicles, and 12,000 miles per year) and 27 million intermittent sustainable resources, such as solar and wind. tons of hydrogen per year for air travel would be needed to Feedstocks, including water, fossil fuels, and biomass, can meet the current energy demand in the United States. produce hydrogen through a number of pathways, includ- With world population growing at a fast pace, the ing electrolysis, thermolysis, and conversion technologies. demand for energy grows, especially in developing nations, Biomass feedstocks can comprise crop residues, forest noted Turner. He commented that the United States needs to residues, energy crops, animal waste, and municipal waste, be concerned about energy usage in developing nations. He and, according to Turner, could have the potential to provide mentioned a quote by C. R. Ramanathan, former Secretary, 15 percent of the world’s energy by 2050. Some challenges Ministry of Non-Conventional Energy Sources, Govern- ment of India: “Energy is the major input of overall social-  Fischer, G. and L. Schrattenholzer, 2001. Global Bioenergy Potentials e ­ conomic development.” According to Turner, the United Through 2050. Biomass and Bioenergy 20: 151-159. 

 BIOINSPIRED CHEMISTRY FOR ENERGY Solar Wind 10 12 14 16 14 16 12 10 12 10 14 16 18 10 Megajoules/m 2 12 <10 10-12 12-14 14-16 16-18 20 22 18-20 24 14 26 20-22 6.0-6.5 m/s 26 13.4-14.6 mph 22-24 24 14 22 2018 24-26 6.5-70 m/s 16 14.6-15.7 mph 26-28 >28 >7.0 m/s 15.7+ mph Biomass Geothermal Agricultural resources residues Wood resources Temperature <90C° and residues Temperature >90C° Agricultural and wood residues Geopressured resources Low inventory 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. 1-2.eps set oblong (but small enough to accommodate a caption), small the energy 4-pt, light with this option include biomass availability, cost, and physi- Direct conversion systems use type is of visible cal and chemical properties. Biomass can provide significant to split water into hydrogen and oxygen. Combining light internal rules are 0.25-pt water-splitting systems into a single system energy, but, said Turner, it is important to remember that its harvesting and main role is to be a food source and it can also be an impor- uses semiconductor, photoelectrolysis, and photo­biological tant chemical feedstock to replace fossil-based feedstocks. systems. According to Turner, the sustainable paths to Turner then explained how electrolysis is a commercial hydrogen are: process that produces hydrogen by splitting water using electricity. This commercial technology can generate hydro- Solar energy → heat → thermolysis → hydrogen gen as an energy carrier using sustainable energy resources, Solar energy → biomass → conversion → hydrogen such as wind and PV, which directly generate electricity. Solar energy → electricity → electrolysis → hydrogen Turner warned of the challenges with some electrolysis Solar energy → photolysis → hydrogen technologies involving the use of platinum group metals, largely due to the high price of the these metals (about $1,300 Growth Rates and Payback an ounce or $46 a gram for platinum, according to Turner). Thermoc­hemical water-splitting cycles handle chemicals and Turner emphasized the importance of growth rates for m ­ aterials under conditions that challenge the current state technology deployment and energy demand. New energy of the art for construction materials and heat transfer fluids. technologies can be a significant challenge but also a ­benefit, For solar energy, such infrastructure needs also include solar depending on the technology. Turner noted that the world- reflectors and thermal storage. Turner does not think that wide demand for energy continues to grow. Thus, alternative thermochemical cycles should be a high priority because they technologies must grow at high rates in to have an impact. are extremely challenging and these thermal-based systems The installation of wind farms, for example, is growing are probably better used to produce electricity. quickly; in fact, wind energy has a 27 percent average 

OVERVIEW—THE ROLE OF BIOINSPIRED CHEMISTRY IN IMPROVING ALTERNATIVE ENERGY TECHNOLOGIES  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 12¢/mi. Therefore, concluded Turner, hydrogen is on par currently supplies less than 1 percent of electricity, Turner with gasoline, and it should not cost much more to implement suggested that its high growth rate would quickly increase its it on a larger scale. market share. If wind could maintain that 27 percent growth He also made a note of future water issues that may need rate, Turner thinks that by 2020 the kilowatt hours from wind to be addressed if hydrogen from water electrolysis is used could surpass that generated from current U.S. nuclear power more frequently. One hundred billion gallons of water per plants. In 2005, production of photovoltaics (PV) rose by year will be required for the U.S. hydrogen-fuel-cell vehicle 47 percent, which is indicative of world demand. If PV could fleet. On the other hand, wind and PV consume no water maintain a growth rate of 30 percent, Turner said PV produc- during electricity production, and thermoelectric power tion would rise to 1 TW per year (peak) in 2028, but because generation utilizes only about 0.5 gallon of water for every of the steady increase in demand, this would only represent kilowatt-hour produced. If wind and solar are aggressively 10 percent of electricity needs. He pointed out that any tech- installed, overall water use will decrease, said Turner. nology that hopes to address carbon-free energy needs should be on the ground now and maintain close to a 30 percent Vision for the Future growth rate for the next 20 years to have an impact. Because coal with carbon capture and storage will take years to get on Turner compared renewable energy and coal with ­carbon ground, it may be too late to make a significant contribution sequestration and explained that he prefers a renewable to future carbon-free energy systems. “If we want a change in energy source because coal resources are finite and it takes the energy infrastructure in the next 50 years or so, we have energy to sequester carbon. To modify or build a new energy to start and maintain these large growth rates in alternative infrastructure requires money and energy—and that energy energy technologies,” said Turner. must come from existing resources. He stated that energy payback—a net gain in energy—is Turner’s vision for the pathway to the future includes another important consideration when choosing the best promotion of renewable energy, developing fuel cells for energy resource. Turner believes that any system without transportation (hydrogen initially from natural gas), imple- net energy payback will eventually be replaced by another menting large-scale electrolysis for hydrogen production energy system. Positive net energy occurs only with energy as sustainable electricity increases, and increasing funding systems that are converting energy from outside the bio- for electrocatalysis. He concluded with: “We have a finite sphere, said Turner—such as for solar (PV) and wind (see amount of time, a finite amount of money, and a finite Table 1.1). However, he added that for PV, growth rates amount of energy, and we need to be very careful about the above 35 percent require a large energy input (e.g., to pro- choices we make as we build any new energy infrastructure. duce the technology), and this leads to an overall negative I’d like to see something that will last for millennia, and energy balance (net loss of energy). Turner noted that wind certainly solar, wind, and biomass will last as long as the is better in this respect, because it still provides an energy sun shines.” payback even at a 40 percent growth rate. Discussion Cost Following Turner’s presentation, some workshop par- Fuel costs for transportation was another issue raised ticipants provided their own thoughts and asked questions in Turner’s presentation. In the United States, gasoline is of the speaker. Daniel Nocera followed up on Turner’s com- currently about $3/gallon, which is 12¢/mile for a 25-mile- ments about energy scale. Nocera said that if a new material per-gallon vehicle. A National Renewable Energy Labora- or new bioinspired approach can be done cheaply, there will tory study has shown that at today’s costs a large wind farm not be the growth rate penalty for PV (above a 35 percent 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  For more information, see the recent NRC workshop summary on “Water Implications for Biofuels Production.” Soon to be released at www. per kilogram, that hydrogen as a transportation fuel is also nap.edu. 

 BIOINSPIRED CHEMISTRY FOR ENERGY growth rate) that Turner mentioned earlier. Scientists can Charles Casey of the University of Wisconsin brought create new technologies to improve the energy payback, up concerns about hydrogen as an energy carrier because according to Nocera. Turner agreed, and said that scientists of infrastructure challenges. He suggested that hydrogen need to find less energy-intensive ways to make energy be converted into hydrocarbons since the infrastructure conversion systems, while also maintaining the growth rate. is already available for hydrocarbons. Turner responded The quicker that more efficient, less expensive materials by stating that the infrastructure really does not exist for and systems are identified, the easier society can move to a synthesis of these proposed hydrocarbons. Carbon dioxide sustainable energy system. would have to be taken out of the air and added to hydrogen Frankie Wood-Black of ConocoPhillips mentioned in order to generate a fuel, which is a huge challenge in the that there can be unintended consequences of new energy United States, said Turner. He argued that a hydrogen infra- systems and that scientists will need to consider these poten- structure does indeed exist since 9 million tons of hydrogen tial unintended consequences when new technologies are is produced every year in the United States. The hydrogen being developed. She used hydrogen and electric cars as an infrastructure is just not in a form that is recognized. 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.