WHAT IS THE CHALLENGE?We are today facing numerous impinging threats on civilization such as overpopulation, declining crude oil reservoirs, or the destruction of the ecological integrity of our planet. In this project, we are addressing two of these burning issues.On one hand, we are trying to develop processes, which can clean air and water from contaminations such as harmful byproducts from industrial processes or emissions caused upon burning fossil fuels. To this end, we rely on energy input from the sun to drive a chemical reaction on the surface of a semiconductor (a material the conductivity of which is intermediate to that of a metal and an insulator). In this scheme, the semiconductor is called a “photocatalyst”, since it enables a light-driven, chemical reaction without itself being consumed or altered. We know today that such photocatalytic reactions are possible, but our understanding of the underlying mechanisms is still comparably poor. Our research focuses on generating a better understanding of how photocatalysts work.On the other hand, we are carrying out research focused on a clean energy carrier, which might substitute oil and coal in the future, namely hydrogen. The idea is to utilize sunlight to split water into oxygen and hydrogen, and thus to store the energy from the sun in the chemical bond of hydrogen. This stored energy can later be regained, for instance when hydrogen is burnt in a combustion engine or a fuel cell. Unfortunately, the process of splitting water with sunlight is typically very inefficient, and consequently the price of the produced hydrogen is high. The reasons for the low efficiency are many and include the often very limited ability of semiconductors to harvest sunlight. Our goals are therefore to improve the light-harvesting ability, to foster a better understanding of the mechanisms underlying water splitting, and to ultimately increase the efficiency of the process.
There are in fact a lot of connections and similarities between the two projects described above; both of them address issues associated with our fossil-fuel based energy system, and both of them involve the use of a semiconductor to harvest sunlight and to catalyze a chemical reaction. Finding a clean energy carrier, which could substitute oil, for instance, would not only solve the problem of limited fossil fuel resources, but could potentially also reduce harmful emissions to the atmosphere.
HOW CAN THE PROJECT CONTRIBUTE TO A SOLUTION?
In order to achieve our goals, i.e. to foster a better understanding of photocatalysis and in particular the water splitting reaction, we utilize advanced nanofabrication methods to fabricate model photocatalysts. The strength of such nanofabricated model systems is that they can be characterized very well, and that their (nano-) structure and chemistry can be tuned accurately. Our aim is to establish a connection between these parameters and the performance of a photocatalyst, respectively. By systematically varying the photocatalyst’s structure and chemistry, we hope to be able to pinpoint what makes a good photocatalyst and to improve the efficiency of photocatalysts for emission cleaning and water splitting.
Additionally, the nanofabrication methods, which we have at hand, allow us to functionalize the photocatalyst with small metallic nanoparticles. Such metallic nanoparticles have been known for very long to have the ability to efficiently interact with light. In fact, the strong and beautiful colors of ancient church windows and renaissance pottery are based on this effect. We hope to be able to utilize nanoparticles made of gold, silver or other metals to remedy one of the weaknesses of many photocatalysts, namely their limited ability to harvest light.
WHO WILL BENEFIT FROM THE RESULTS?
In the nearest future, the results generated within this project are expected to have an impact on other scientists, who hopefully will be able to build on our results in order to generate an even better understanding of photocatalysis. As time goes, we should be able to fabricate more and more sophisticated photocatalysts with better and better efficiency. On a longer time-scale, the output of this project is therefore likely to have an impact on each and everyone of us, in as much as the results of the project can be used to build efficient photocatalysts for emission cleaning and water splitting. The result would be a cleaner environment and an energy-system, which is based on a renewable energy source and a renewable energy carrier in the form of hydrogen. Companies in the clean-tech sector are the prime candidates to exploit and commercialize results of technological importance.
