Editorial pubs.acs.org/jchemeduc
Energy in the Age of Sustainability Héctor D. Abruña* Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, United States ABSTRACT: Meeting global energy needs in a sustainable and environmentally responsible way is one of the grand challenges of our time. While the use of energy based on fossil fuels has enabled great advances and an increase in the standard of living, it has also brought us to the brink of an environmental catastrophe. As a society, we will need to develop strategies that integrate renewable and sustainable energy sources. We must also engage and partner with policy makers in order to articulate an energy policy that is not only scientifically and technically sound, but also one that the global society will accept. The energy challenge is the type of problem that we, as a global society, have never faced before and we need decisive scientific and political leadership to address it. We must accept the challenge and insist that our leaders articulate a global energy policy capable of meeting such a challenge. (Image created by Alice Muhlback and used with permission.) KEYWORDS: General Public, Environmental Chemistry, Public Understanding/Outreach, Atmospheric Chemistry, Catalysis, Electrolytic/Galvanic Cells/Potentials, Electrochemistry, Oxidation/Reduction, Materials Science, Photosynthesis
E
nergy: its mere sound evokes a broad range of reactions depending on our experience, education, political affiliation, and many other factors. The word is part of our everyday lexicon in terms of the cost of energy (when we actually mean the cost of fuel), global availability of energy and the inevitable geo-political analysis, the environmental consequences of energy use, carbon footprint, global warming, emerging economies, population growth...you get the idea. Energy is part of virtually every aspect of our lives, local and global. Energy is also a subject of big numbers such as “quads” (quadrillion BTUs), Terawatt-years, and gigatons (usually of generated CO2). As chemists, actually as citizens (better yet, as informed citizens), we need to grapple with these concepts and the magnitude of these numbers to get a realistic assessment of what they mean and how our collective behavior affects them and the future of our planet. (See Figure 1.) Energy availability, in a reliable and inexpensive way, has been key to technological advances and innovation, which, in turn, have enhanced our standard of living. One can readily identify and acknowledge that developments such as the steam engine, the incandescent lamp, the internal combustion engine and the computer, just to name a few, have transformed the way we live and interact with each other. All of them have a common thread of depending on an energy source, albeit different in each case, to accomplish a particular function. This brings us to the description of energy in terms closer to those associated with thermodynamics, mainly as the ability to do work. So the question is, how are all of these issues interrelated, and what role do we, collectively, play?
Figure 1. Depiction of the global energy challenge. The image illustrates how we must transition (gray-to-green arrow) from fossil fuels (gray smoke stacks in the background) to sustainable and renewable sources, and capture and store the energy (bottle with sun and cloud) so as to enable us to “power” our planet (small yellow person with electric plug). The mother represents the current generation and how we must be good stewards of our planet so as to hand it over to the next generation (children) in better shape. The importance of efficient use of energy is depicted by the hand holding a compact fluorescent bulb. (Image created by Alice Muhlback and used with permission.)
considering energy generation and consumption. Through the middle to end of the past decade, global energy consumption was approximately 500 quads.1 (In this context, quads represent a convenient unit as comparisons are easy to establish.) Of those, the United States consumed about 100 quads.1 Thus, while we represent only 5% of the world’s population, we
■
QUANTIFYING ENERGY USE The intent of this Editorial is to provide some basic concepts and numbers regarding energy in the age of sustainability and what some future prospects might be. Let us begin by © 2013 American Chemical Society and Division of Chemical Education, Inc.
Published: November 12, 2013 1411
dx.doi.org/10.1021/ed400673m | J. Chem. Educ. 2013, 90, 1411−1413
Journal of Chemical Education
Editorial
consume about 20% of the global energy production.1 It is projected that by 2050 world energy needs will double!2 Currently, over 85% of world energy production is obtained from fossil fuels (oil, coal, and natural gas (especially shale gas in recent times));3 nuclear provides about 6−7%,3 and the balance comes from biomass and hydro with a relatively small contribution from other renewable sources (e.g., solar photovoltaic and wind).3 A direct consequence of the use of fossil fuels has been the increase in carbon emissions, which was about 6.6 gigatons in 20014 and is projected to reach about 11.0 gigatons by 2050.4 Current levels of CO2 in the atmosphere are approaching 400 ppm5 and, without intervention, are projected to increase in an accelerated fashion. The environmental, economic, political, and health consequences of such increases will likely be catastrophic. While estimates vary, proven global reserves of oil are somewhere in the range of 40−80 years, 207−590 years of natural gas, and somewhere between 1000−2000 years of coal.6 While it is certainly a truism that “we will eventually run out of fossil fuels”, that day is not imminent. However, the consequences of the continued use of fossils fuels are. In particular, the cumulative emission of CO2 and related greenhouse gases is of particular concern. In this context, the global carbon budget (the environment’s ability to assimilate carbon without increasing average global temperature by 2 °C) is estimated at a trillion tons.7 We have used over 50% of that budget, and extrapolating current trends, we will exceed the budget by about 2050,7 long before we run out of fossil fuels. Thus, globally we will need to satisfy our energy needs with sources other than fossil fuels, not because we will eventually run out (which we will), but because the environmental consequences, of which climate change is but one, will be catastrophic long before that. We need to identify, develop, and deploy strategies that will be capable of delivering, in a sustainable way, the energy we require, while mitigating and adapting to changes already underway. What are some options?
source, rather, it is an energy storage medium. In addition, any analysis must also account for the way hydrogen is produced.) While the adoption of fuel cells for automotive applications has seen tremendous advances in the recent past, they are still not available in the market. However, recent developments at GM, Toyota, and other automobile manufacturers suggest that they may reach the market in limited quantities by 2015. Turning to renewable and sustainable sources of energy, the ones most frequently mentioned are solar, wind, and tidal. Of these, there is no doubt that the most promising is solar. In fact, the amount of energy from the sun hitting Earth in 1 h is more than the total global consumption of energy in one year! This was evident to Edison who in 1931, in a conversation with Henry Ford and Harvey Firestone, said (in a prophetic way), “I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait until oil and coal run out before we tackle that.”11 In essence, the sun is the only source that can realistically provide the energy (in a carbonneutral way) that we need now and into the future. Solar energy utilization requires two basic aspects, energy capture/ conversion and energy storage. Solar energy capture can be achieved through the use of photovoltaic devices. This, however, will require significant advances so that the average cost per kWh is price competitive with other sources. Currently, we are only about a factor of 2 to 3 times away from that (depending on regional availability, price of competing energy systems and installation costs). Because of diurnal variations in solar irradiation and fluxes, these technologies can only operate for part of the day. Thus, in order for solar energy to truly represent a primary energy source, we will need to develop high-performance, cost-effective electrical energy storage technologies on a vast scale. While there have been great advances in this field,12 viable systems in terms of performance, costs and lifetime are currently not available. An alternative is to use solar energy to generate fuels (often referred to as “solar fuels”). Of particular interest and importance has been the use of solar energy to achieve the photodecomposition of water into hydrogen and oxygen. This requires the integration of light absorbers to generate and separate electrons, and holes that are subsequently used to drive hydrogen and oxygen evolution at suitable catalytic surfaces that are, in turn, separated by a membrane. (Conceptually, these systems represent fuel cells run in reverse.) In addition, there is significant interest in the reduction of CO2 to generate carbon-based fuels. This approach has the attractive feature of using CO2 as a feed. (However, it should be noted that this would be carbon-neutral because one would simply recycle the CO2.) In either case, the generated fuels would be stored and used when needed, for example, in a fuel cell.
■
POTENTIAL SUSTAINABLE ENERGY STRATEGIES We can think of strategies that involve the efficient use of energy as well as the use of renewable and sustainable (carbonneutral) energy sources. For example, an incandescent light bulb is about 2% efficient in its conversion of energy to light.8 2%! To overcome this, a new generation of efficient light sources, such as compact fluorescent bulbs (Figure 1) and LEDs (light emitting diodes), have been developed. A second example comes from the internal combustion engine (ICE), or from the thermodynamic standpoint, heat engines, in general. A Carnot cycle analysis shows that an ICE engine has a theoretical efficiency of about 45−50%, depending on actual operating temperatures. (Recall that the Carnot efficiency η is given by: η = (TH − TC)/TH, where TH and TC are the hot and cold temperatures of the appropriate reservoirs.) In reality, a typical gasoline car engine is about 25% efficient in its energy use.9 Put in different terms, 75% of the energy content (recall ability to do work; strictly speaking, this refers to free energy) of the fuel is wasted! This inefficiency has ushered the development of diesel engines, hybrid systems, and fuel cells for automotive applications. Fuel cells convert chemical energy (often with hydrogen as fuel and oxygen as oxidizer) directly to electricity and thus are not constrained by the Carnot cycle limitations. In principle, a fuel cell could exhibit efficiencies around 90%, or even higher.10 (It is worth mentioning that contrary to popular perceptions, hydrogen is not an energy
■
EFFORTS NEEDED TO BUILD A SUSTAINABLE ENERGY SYSTEM So where do we find ourselves in this landscape? Without a doubt, there have been significant developments in these areas, especially with regards to new materials. However, the deployment of a practical, efficient, long-lived, and low-cost system is still decades away. Even if we had such devices today, deployment of a vast new infrastructure and the related financial, social, and political paths to get there will likely take decadesbut at the current pace much longer. Similarly, there have been significant advances in developing devices for solar generated fuels at JCAP (the Joint Center for Artificial 1412
dx.doi.org/10.1021/ed400673m | J. Chem. Educ. 2013, 90, 1411−1413
Journal of Chemical Education
Editorial
(5) National Oceanic and Atmospheric Administration, Earth System Research Laboratory. Trends in Atmospheric Carbon Dioxide. http:// www.esrl.noaa.gov/gmd/ccgg/trends/ (accessed Oct 2013). (6) See, for example: U.S. Energy Information Administration. International Energy Statistics. http://www.eia.gov/countries/data. cfm (accessed Oct 2013). (7) Allen, M. R.; Frame, D. J.; Huntingford, C.; Jones, C. D.; Lowe, J. A.; Meinshausen, M.; Meinshausen, N. Warming Caused by Cumulative Carbon Emissions towards the Trillionth Tonne. Nature 2009, 458, 1163−1166. See also Meinshausen, M.; Meinshausen, N.; Hare, W.; Raper, S. C. B.; Frieler, K.; Knutti, R.; Frame, D. J.; Allen, M. R. Greenhouse Gas Emission Targets for Limiting Global Warming to 2 °C. Nature 2009, 458, 1158−1162. (8) Murphy, T. W., Jr. Maximum Spectral Luminous Efficacy of White Light. J. Appl. Phys. 2012, 111, 104909. (9) U.S. Department of Energy. Fuel Economy: Where the Energy Goes. http://www.fueleconomy.gov/feg/atv.shtml (accessed Oct 2013). (10) COGEN Europe. New and Emerging CHP (Combined Heat and Power)Fuel Cells. http://www.cogeneurope.eu/new-andemerging-chp_273.html (accessed Oct 2013). (11) Quoted in Newton, J. Uncommon Friends: Life with Thomas Edison, Henry Ford, Harvey Firestone, Alexis Carrel, and Charles Lindbergh; Harcourt: San Diego, CA, 1987; p 31. (12) (a) Abruña, H. D.; Kiya, Y.; Henderson, J. C. Batteries and Electrochemical Capacitors. Phys. Today 2008, 61, 43−47. (b) Lowe, M. A.; Gao, J.; Abruña, H. D. In Operando X-ray Studies of the Conversion Reaction in Mn3O4 Lithium Battery Anodes. J. Mater. Chem. A 2013, 1 (6), 2094−2103, DOI: 10.1039/c2ta01270g. (c) Burkhardt, S. E.; Lowe, M. A.; Conte, S.; Zhou, W.; Qian, H.; Rodríguez-Calero, G. G.; Gao, J.; Hennig, R. G.; Abruña, H. D. Tailored Redox Functionality of Small Organics for Pseudocapacitive Electrodes. Energy Environ. Sci. 2012, 5 (5), 7176−7187, DOI: 10.1039/c2ee21255b. Also see: Abruña Group Electrochemistry Laboratory at Cornell University. http://abruna.chem.cornell.edu/ index.html (accessed Oct 2013). (13) Joint Center for Artificial Photosynthesis (JCAP). http:// solarfuelshub.org/ (accessed Oct 2013). (14) Joint Center for Energy Storage Research (JCESR). http:// www.jcesr.org/ (accessed Oct 2013). (15) Energy Frontier Research Centers (EFRCs). http://science. energy.gov/bes/efrc/ (accessed Oct 2013). (16) U.S. Department of Energy, Basic Energy Sciences, Reports Web page. http://science.energy.gov/bes/news-and-resources/ reports/basic-research-needs/ (accessed Oct 2013).
Photosynthesis at Cal Tech and Lawrence Berkeley Laboratory).13 There is a great deal of expectation from the newly established JCESR (Joint Center for Electrical Storage Research) at Argonne National Laboratory.14 In addition, a number of the 46 EFRCs (Energy Frontiers Research Centers) nationwide are also involved in these areas.15 It should be mentioned that, JCAP, JCESR, and the EFRCs are all DOEbased programs that emerged from a group of reports on “basic research needs”.16 In this context, the DOE should be commended for these efforts. Having said that, however, we must also recognize that these programs, in reality, represent a down-payment and that dramatic increases in support will be necessary in years to come if we are to build a sustainable energy system. While there have been significant scientific and technological advances, there are also monumentally difficult societal and political problems to be resolved. This is clearly the realm of social scientists, policy makers, and opinion leaders. As scientists, we need to engage and partner with these groups because the best technological solutions will fall short of the intended objectives if citizens are not informed and ready to be part of the process. The energy challenge is the type of problem that we, as a global society, have never faced before and we need decisive scientific and political leadership to address it. We must accept the challenge and insist that our leaders articulate a global energy policy capable of meeting such a challenge. Both action and inaction have consequences, and the time to start is now.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Héctor D. Abruña is a professor in the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, as well as director of the Energy Materials Center at Cornell (EMC2).
■
ACKNOWLEDGMENTS This work was supported by the Department of Energy though grant DE-FG02-87ER45298, by the Energy Materials Center at Cornell, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001086. I would like to thank Frank DiSalvo, Paul Mutotlo, and Rubén Abruña for their comments and critical reading of this manuscript.
■
REFERENCES
(1) U.S. Energy Information Administration. How Much of the World’s Energy Does the United States Use? http://www.eia.gov/ tools/faqs/faq.cfm?id=87&t=1 (accessed Oct 2013). (2) Ghouri, S. S. Global Energy Outlook 2050Policy Options. http://www.worldenergy.org/documents/p000616.pdf (accessed Oct 2013). (3) International Energy Agency. Key World Energy Statistics from the IEA. http://www.iea.org/publications/freepublications/ publication/KeyWorld2013_FINAL_WEB.pdf (accessed Oct 2013). (4) Lewis, N. S.; Nocera, D. G. Powering the Planet: Chemical Challenges in Solar Energy Utilization. Proc. Natl. Acad. Sci. U.S.A. 2006, 103 (43), 15729−15735. 1413
dx.doi.org/10.1021/ed400673m | J. Chem. Educ. 2013, 90, 1411−1413
