Our energy systems will have to change during the next decades, and we have to initiate the changes soon. This is required for two main reasons. The first reason is that although it is unclear when “peak oil,” that is, the point in time at which in spite of all efforts the production of oil can not be increased any more, will come, it is clear that oil is a finite resource, and the same holds for natural gas, even if it is expected that gas reserves will reach further into the future by several decades. We will thus need to replace—to an increasing extent—a source of energy that at present satisfies the major part of the world’s energy demand. The second reason may be felt in its full force by mankind later, but the consequences could be even more severe: global warming, almost certainly brought about by increasing levels of greenhouse gases in the atmosphere. The burning of fossil fuels, be it for generating electricity, for powering our cars, or for heating our homes, is the major contributor to CO2 emissions into the atmosphere.
A “decarbonization” of our energy systems is thus one of the most important tasks for the future. This could be brought about by different approaches that most certainly have to supplement each other to restrict global warming to less than 2 °C, which is considered to be just the acceptable level by many scientists. The options range from different technologies for increased energy efficiency over methods for CO2 capture and sequestration, increasing shares of renewable, CO2-neutral sources of energy, to the possible continuing use of nuclear energy, at least as a transition technology. If one analyzes the demands placed upon us by the adaptation of our energy systems, it becomes clear that chemistry plays a pivotal role in most technology options. Almost any conversion of energy from one form into another involves a chemical transformation, and understanding the fundamental nature of these reactions is key for the development of new materials and energy transformation pathways. However, one should always keep in mind that questions concerning our energy systems are highly interdisciplinary in nature, where all branches of science and engineering have to work together, and even beyond science and engineering: the questions to be solved are certainly not only of a technological nature, but touch many different fields of the social sciences and the humanities as well, such as sociology, law, economy, psychology, and others. For example, we now have proven technologies for better insulation of homes which on the long run would even reduce costs; however, in spite of this advantage many house owners are not implementing these technologies, and research is needed into the motives for this reluctance and into instruments which may help to lower the barriers for the implementation of efficiency technologies. Another prominent example is the Desertec-project,1 which has been initiated by a consortium of mostly German companies to provide about 15 % of the European electricity demand in 2050 by renewable energy, mostly generated in solarthermal power plants in southern Europe and North Africa. This project is certainly a formidable technological challenge, but there are other challenges of a sociological and political nature, for example: How to make such systems, in which a few high-voltage DC power lines would transmit the power to central Europe, less susceptible against terroristic attacks or political blackmail? What are the means by which the transit countries would allow the construction of power lines through their territory? How would one construct cities for workers who would operate such gigantic plants in rather hostile environments, such as the Sahara desert?
While many different branches of science have to combine their forces to reshape our energy systems, the central role of chemistry is quite obvious. This has recently been highlighted by several events organized by the chemical societies of different countries, such as various meetings, workshops, and conferences, or white papers and other publications. A dedicated joint workshop, the CS3-meeting, took place at the end of July 2009: representatives of the American Chemical Society (ACS), the Chemical Society of Japan (CSJ), the Chinese Chemical Society (CCS), the German Chemical Society (GDCh), and the Royal Chemical Society of the UK (RSC) came together in the Seeon monastery in southern Germany to discuss the contributions of chemistry for tapping into the most abundant and widely available source of energy mankind has, that is, the energy of the sun. The results of this meeting are summarized in a paper that is available on the homepages of the participating societies.2
In approximately just one hour, the sun provides enough energy for the total yearly energy demand of the world at the present level. Figure 1 shows how much area of the Sahara desert would be required, at a conversion efficiency of 10 %, to supply the total world population with energy, according to the consumption of a European citizen (5 kW power per person).
We are thus not really facing a crisis in energy supply, but we certainly have to find more intelligent and affordable means to harness solar energy and make it useful for mankind. During the Seeon workshop, four different topics were discussed, which have high relevance if an increasing fraction of our energy needs should be supplied by solar energy: (1) the direct use of solar energy by artificial photosynthesis, photocatalytic water splitting, and CO2 fixation; (2) the conversion of solar energy into biomass, which is then in turn used as a source of energy; (3) the direct use of solar energy via photovoltaics and related technologies; and (4) systems questions, which are mainly questions of storage and transportation of discontinuously supplied energy, of which solar radiation is one example, but another renewable energy source, that is, wind energy (eventually also supplied by solar radiation) is the other important contributor. It was agreed that specific research priorities exist for all the different topics, although interest in different fields might vary for different regions of the world. The essential messages will be briefly highlighted below.
Importantly, the research priorities do not only address important questions for our societies, they are also targeted at some of the most fundamental questions in chemistry. For example, in the field of direct photocatalytic water splitting the development of suitable catalysts for this multi-electron-transfer reaction would be a major breakthrough. Many discoveries of a fundamental nature would be required to achieve this task; for example, it appears clear that systems which could operate for longer periods of time have to involve elements of self-repair, just as the natural photosystem has an intricate self-repair mechanism. Even more challenging than the direct water splitting reaction itself would be coupling of this reaction with CO2 reduction, which would probably have to involve the construction of chemical systems in which different components have different tasks and must work in a concerted manner; a field that is currently just emerging.
Tapping into biomass as a source of energy and raw materials is an indirect way of using the energy of the sun, and many different pathways already exist or are being developed. However, many of them do not appear to be sustainable, and the problem of competition with food and feed always has to be considered. The challenges here are manifold: it appears important to make increasing use of lignocellulose biomass, but this poses questions with respect to breaking down this rather recalcitrant biopolymer. If this succeeds, there is still novel and exciting chemistry to be developed. Chemists have been trying to develop ever-more-sophisticated methods for the controlled functionalization of simpler molecules. However, if biomolecules should be converted into fuels or chemicals, rather controlled defunctionalization chemistry is required, for which not many methods yet exist. On the side of chemistry bordering to biology, methods should be explored by which the productivity of plants can be improved, for example by a better understanding of the metabolic and genetic pathways that control the growth of plants.
The research priorities for various kinds of photovoltaic devices are rather clear: in general, photovoltaic systems work, but they are currently too expensive, and those systems that allow high conversion efficiencies often rely on rare, expensive, and/or toxic compounds. The development of cheap, earth-abundant, and nontoxic photovoltaic materials is thus very high on the priority list in this research area, either by the use of alternative inorganic materials, by the development of new generations of dye-sensitized cells, or by breakthroughs in the development of organic solar cells.
On the systems level, a key problem of energy that relies on solar radiation is its discontinuous, intermittent nature. This property, which is shared with wind energy, requires the development of storage materials and systems for all sizes and time scales, from short-term storage for bridging the dark hours during the night to long-term, large scale storage in chemical compounds as strategic energy reserves or for bridging seasonal changes in renewable energy supply. Some of the fluctuating energy will be buffered by advanced electricity grids, but certainly a strong need for storage systems will remain, most of which will rely on chemical solutions.
Beyond these more specific points, there are a number of more general issues related to energy oriented chemistry research. It is clear that the energy technology of the future can only be built on a solid foundation of scientific discoveries today. This statement can be supported by a simple example. Zeolite research in the middle of the 20th century initially resulted in the discovery of nice, porous alumosilicate structures; wonderful scientific discoveries. However, it was soon found that this class of materials also provided excellent catalysts for the petrochemical industry, and it is estimated that the introduction of zeolite cracking catalysts, instead of the previously used amorphous alumosilicates, alone has led to savings of 400 million barrels of crude oil per year.3 Thus, a scientific discovery was quickly converted into one of the most important energy technologies today. Such technology development needs a broad foundation of chemistry research. And it is not only research, but more importantly also skilled and resourceful researchers that are urgently needed. If students find fascination in chemistry targeted at solving energy questions, they will be the energy scientists of the future, and we should do all we can to foster research in this direction.
It is interesting to ask what the benefit of such a joint workshop is. There are three major effects this event could have. Firstly, it was certainly for the benefit of the participants who were all specialists in their own fields, but expanded their knowledge on other aspects of energy-related chemistry research, and it led also to the overall consensus that the problems discussed are global problems, even if they may take different shades in different parts of the world. Secondly, the chemical societies are sending a message to political decision makers and to the funding agencies who were present at the workshop. Consensus on priorities amongst scientists could help to shape future research programs. Finally, such events also serve as a means of communication to the chemistry community itself, activating colleagues to direct their research more towards one of the most pressing problems we are facing nowadays, and it can only be hoped that as many colleagues as possible will study the documents provided and will find inspiration for their own research.
The white paper as a result of the CS3 meeting in Seeon is not the only publication highlighting the role of chemistry in energy science. Other recommendations have been formulated along similar lines. For example, the chemistry organizations of Germany (Bunsengesellschaft, Dechema, DGMK, GDCh, VCI, and VDI–GVC) have produced three white papers of somewhat wider scope, trying to more comprehensively encompass the contributions of chemistry to most energy technologies, not only restricted to forms of solar energy.4 The first paper is a relatively short one, highlighting certain topics. In the second paper from 2007, the contributions of chemistry to various different energy technologies are discussed in more detail. But especially the most recent of these three papers is interesting in that it tries to quantify the contributions that chemistry research could provide to our future energy demand. While it is very difficult to arrive at exact numbers, it is estimated that progress by research in chemistry alone could provide an additional 20 % of the future energy demand of the world, by a combination of many smaller contributions in different fields of energy technology. If one takes into account the possibilities that are there with today′s technology, and in addition considers the progress expected in other fields of science and technology, one can be moderately optimistic that the two challenges listed in the beginning, the dwindling of oil and gas reserves and global warming, can be met with reasonable success. However, it will not be easy and it will require many bright minds to develop the solutions that are today only on the horizon, or sometimes even still below it. If we have these solutions, we should not be content and stop at this point, we have to do all that is possible to implement them, and scientists have the ability and the obligation to exert their influence on decision makers and the public to work together for a sustainable and safe energy future.