More and more devices are connected, and we carry myriad electronic gadgets around with us. But what about the power supply? Perhaps we can become our own personal generators. At Christian Müller’s laboratory the aim is to convert body heat into electricity.
Professor of Polymer Technology
Wallenberg Academy Fellow 2014
Chalmers University of Technology
Polymeric semiconductors in thermoelectric generators and solar cells
“Twenty years ago we might have carried a single electronic device. Nowadays we have many more, and in twenty years’ time far more devices will be connected to the internet. It will be impossible to run everything on batteries. Instead, we need to develop really inexpensive technologies capable of providing a power supply for each device. Solar cells are one solution – but only if there is sun. But differences in temperature are all around us, and we could use them to create exactly the amount of electricity needed to run an electronic device,” says Müller, who is a Wallenberg Academy Fellow based at the Department of Chemistry and Chemical Engineering at Chalmers University of Technology.
The idea is not new: thermoelectric generators have been around for several decades. If the temperature in a conductor or semiconductor varies from one of its parts to another, this may set electrons in motion, i.e. create an electric current. Optimally doped semiconductors produce most power; by connecting them in series enough power can be generated to run devices. This technology is used in space probes, for example. A thermoelectric generator is installed in the probe, and connected up to a radioactive substance that decays and thus generates heat. The generator powers the probe much longer than solar panels could, as the probe moves away from the sun.
Plastics cut manufacturing costs
“Nonorganic materials have been used to date, and the generators have been expensive to make. I want to develop thermoelectric generators based on organic materials, such as polymeric semiconductors. They could be much cheaper,” Müller says.
Polymers are materials, usually plastics, consisting of molecules arranged in chains. Thermoelectric plastics would be flexible and bendable; they could be braided and woven into the desired size and shape or printed on a 3D printer. This would make the manufacturing process itself much more cost-effective than the present method, which requires micro manufacture of each thermogenerator.
The new materials could be woven into a garment and could run earphones, sensors or RFID (radio frequency identification) tags, which are used in travel cards and electronic keys, for example. But the technology needs to be more efficient. Currently available thermoelectric materials have to cover an area about the size of the palm of a hand to run a clock. That is too big.
“When I received my first grant from the Swedish Research Council I was pretty much part of the system. Being named a Wallenberg Academy Fellow means that I feel welcome in Sweden – appreciated for what I am doing here. I think that is what I am most grateful for. It’s not like that everywhere.”
Fun making a new material
In addition, current plastic semiconductors cannot be woven or printed. Their chains of molecules are too short, which makes the plastic brittle. Müller will be trying to create plastics possessing better mechanical properties.
“I have been working on polymeric semiconductors for quite some time, albeit mostly as thin layers affixed to another material. In that case mechanical properties are no great problem. But thermoelectronics demands much thicker materials. I like making new materials, and I realized that thermoelectricity was a fantastic testing ground for developing new materials possessing both good electronic and good mechanical properties,” Müller enthuses.
His project is a collaborative one. He has one colleague in his own research team who used to work at the Swedish School of Textiles in Borås. Müller says he knows a fair amount about fibers, but less about how they can be put together to form fabrics. It is here that his colleague’s expertise can be put to good use.
Research as a fashion show
Müller has studied and researched in Zurich, Barcelona, Linköping, Cambridge, and elsewhere. Having tried physics and chemistry he opted for materials science and for physical chemistry, a field appreciated by few of his fellow students. He became increasingly fascinated by plastics, not least because the field offered potential for interesting collaborative projects with industry.
“But as far as organic thermoelectric plastic is concerned, there is no industry yet. I see our research as a fashion show instead. After all, the creations presented by fashion houses are not intended to be worn by anyone on the street. They generate interest by showing what can be done with clothes. We do the same. We are fairly philosophical – dreaming of what could be done with plastics. And I hope that my students take things a step closer to practical applications in the future.”
That is Müller’s big dream: To see his doctoral students in industry or the academic world, and to have given them a good start in their careers.
At the moment he is on part-time parental leave. Much of the time he is at work is spent on administration – although he does point out that Sweden is not as bad in this respect as many people claim. He sighs, mentioning that he has worked in many countries that really love official stamps. Form after form has to be filled out if anything is to get done.
“Looking to the future, I will have to decide whether I want to work on small or large-scale projects. Both have their attractions. If I become involved in something on a larger scale, it will be because I like to see others succeed. As a researcher in those situations you have to take more of a back seat.”
Text Lisa Kirsebom
Translation Maxwell Arding
Photo Magnus Bergström