Our world is at present mostly running on fossil fuels – oil, coal and natural gas – using energy harnessed from the sun and stored by photosynthetic organisms many million years ago. The rapid exploitation of these valuable resources over the last 2 centuries, which are not renewable on a human time scale, has led to inevitable shortages - and the economic, social and political consequences are already being felt today. Furthermore the burning of carbon-rich fuels has increased CO2 concentrations in the atmosphere that are related to climate changes with many adverse effects for our planet and human society. Human population and economic growth, particularly in fast-developing countries, will lead to further increases in energy demand.
It is therefore one of the great challenges of mankind to identify and develop alternative sustainable energy sources. The extensive use of nuclear energy has no support in our society and many countries have therefore decided to discontinue this technology. The prospected nuclear fusion reactors are still in the early development stage. Alternative physical energy conversion techniques, for example based on hydrodynamic power, wind-propelled generators and photovoltaic devices, are increasingly used to generate electricity, but suitable techniques to directly obtain large quantities of fuels in a renewable way, e.g. to replace gasoline and diesel, are still lacking. Here the exploitation of solar energy has enormous potential. The problem is developing technologies that allow this energy source to be efficiently captured and converted not only to heat or electricity but stored in form of chemical fuels.
Chemical bonds are the best way to store energy – by far superior to batteries and mechanical devices. The efficient production of a clean storable “solar fuel” would therefore represent a very important breakthrough in the chemical sciences. Such a fuel must be made from abundant, inexpensive, non-toxic materials such as water, which could be split by light into molecular oxygen and hydrogen (“artificial photosynthesis”). Molecular hydrogen is considered the ideal primary fuel of the future, since its combustion yields only water as waste product. Furthermore it can be converted to many other important energy-rich materials (e.g. with CO2 to methane, methanol, hydrocarbons) for further storage and transport. These compounds also have uses in other industrial sectors.
Enormous scientific, technological and economical efforts are needed to initiate the “Energiewende” (energy transition) – away from the dominance of fossil energy carriers. Future energy systems will be based substantially on renewable solar primary energy but cannot be operated without a suite of technologies of chemical energy conversion dealing with storage and interconversion of energy carriers. The central discipline in this endeavor is catalysis. In this respect much can be learned from Nature which has developed many metallo-enzymes for the conversion of small molecules with low overpotentials, high turnover numbers, long lifetimes and build-in protection and repair mechanisms.
This topic – and in particular the place of chemistry in this endeavor – will be discussed in the panel discussion with several Nobel Laureates.