Scientists are making progress in creating an “artificial leaf” that mimics a real leaf’s chemical magic with photosynthesis — but instead converts sunlight and water into a liquid fuel such as methanol for cars and trucks. That is one of the conclusions in a newly-available report from top authorities on solar energy who met at the 1st Annual Chemical Sciences and Society Symposium. The gathering launched a new effort to initiate international cooperation and innovative thinking on the global energy challenge. Scientists hope to develop chemical catalysts for the two major processes of artificial photosynthesis --water splitting and CO2 reduction -- that can be applied commercially and are made of affordable, earth-abundant materials.
The sun provides more energy to the earth in an hour than the world consumes in a year. Compare that single hour to the one million years required for the earth to accumulate the same amount of energy in the form of fossil fuels. As the global population continues to expand and with life expectancies increasing worldwide, scientists estimate that total energy consumption of the world will more than double by 2050 if society continues to use energy at its current rate. While silicon-based photovoltaic (PV) cells are the most common way of using solar energy, the high cost of purified silicon limits its widespread use. No matter how efficient an energy conversion technology is, much of the world will not be able to use it unless it is also affordable.
According to Dr. Alvin Compaan, University of Toledo, Ohio, about 20 terawatts (TW) of electricity were produced worldwide in 2008. Only 7 gigawatts (GW) of that 20 TW (0.035%) were in the form of PV modules. Widespread use of PV technology is limited by the high cost of silicon. Most PVs currently being manufactured and used worldwide are made of solar-grade silicon (Si).
The three-day symposium, which took place in Germany this past summer, included 30 chemists from China, Germany, Japan, the United Kingdom and the United States. It was organized through a joint effort of the science and technology funding agencies and chemical societies of each country, including the U. S. National Science Foundation and the American Chemical Society (ACS), the world’s largest scientific society. The symposium series was initiated though the ACS Committee on International Activities in order to offer a unique forum whereby global challenges could be tackled in an open, discussion-based setting, fostering innovative solutions to some of the world’s most daunting challenges.
The symposium focused on four main topics:
• Mimicking photosynthesis using synthetic materials such as the “artificial leaf”
• Production and use of biofuels as a form of stored solar energy
• Developing innovative, more efficient solar cells
• Storage and distribution of solar energy
The scientists pointed out during the meeting that plants use solar energy when they capture and convert sunlight into chemical fuel through photosynthesis. The process involves the conversion of water and carbon dioxide into sugars as well as oxygen and hydrogen. Scientists have been successful in mimicking this fuel-making process, termed artificial photosynthesis, but now must finds ways of doing so in ways that can be used commercially. Participants described progress toward this goal and the scientific challenges that must be met before solar can be a viable alternative to fossil fuels.
Highlights of the symposium included a talk by Kazunari Domen, Ph.D., of the University of Tokyo in Japan. Domen described current research on developing more efficient and affordable catalysts for producing hydrogen using a new water-splitting technology called “photocatalytic overall water splitting.” The technology uses light-activated nanoparticles, each 1/50,000 the width of a human hair, to convert water to hydrogen. This technique is more efficient and less expensive than current technologies, he said.
Domen noted that the ultimate goal of artificial photosynthesis is to produce a liquid fuel, such as methanol, or “wood alcohol.” Achieving this goal would fulfill the vision of creating an “artificial leaf” that not only splits water but uses the reaction products to create a more usable fuel, similar to what leaves do.
Among the “take-home messages” cited in the report:
• There’s no single best solution to the energy problem. Scientists must seek more affordable, sustainable solutions to the global energy challenge by considering all the options.
• Investing in chemistry is investing in the future. Strong basic research is fundamental to realizing the potential of solar energy and making it affordable for large-scale use.
• Society needs a new generation of “energy scientists” to explore new ways to capture, convert, and store solar energy.
