Researchers at the Laboratory for Organic Electronics at Linköping University, Sweden, have created a condenser that can be charged by heat. The condenser works well enough with enough capacity it can be called a supercondenser. The new design contains no expensive or hazardous materials, has patents pending, and it should be fully possible to manufacture it on an industrial scale.

Storing heat as electricity. Image Credit: Linköping Universitet. Click image for the largest view.

Storing heat as electricity. Image Credit: Linköping Universitet. Click image for the largest view.

The research paper has been published in the journal Energy Environmental Science.

The future could have a completely new type of energy storage, charged by heat energy – for example during the day when the sun shines, or by waste heat from an industrial process. The heat is converted to electricity, which can be stored until it is needed.

A condenser or supercondenser is a type of energy storage, similar to a battery, that consists of an electrolyte of charged particles – ions – between the two electrodes. The charge is stored next to the electrodes, most often in carbon nanotubes. One of the physical phenomena that the researchers make use of here is that if a supercapacitor is exposed to a temperature gradient – that is, one end is warm and the other cold – the ions rush towards the cold side and an electric current arises.

As a practical matter the terms supercondenser and supercapacitor can be but are not always interchangeable with condenser being the older term and capacitor the more modern one.  Here we’re going with the Swede’s choice of condenser likely due to the effect of heat on the capacitor being a means of charging.

The thermoelectric effect uses heat to generate electricity – how much heat is converted to electricity depends both on which electrolyte is used and how great the temperature difference is. The thermoelectric effect has many identifiers, thermophoresis also thermomigration, thermodiffusion, the Soret effect, or the Ludwig-Soret effect. It is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different responses to the force of a temperature gradient.

For many years, researchers at the Laboratory for Organic Electronics have experimented with fluid electrolytes consisting of ions and conductive polymers. The positively-charged ions are small and quick, while the negatively-charged polymer molecules are large and heavy. When one end is heated and the other one cooled down, the small, quick ions rush towards the cold side while the heavy polymer chains stay where they are. Since they are ions, and not electrons, they stick to the metal electrodes. The charge that then arises is stored in carbon nanotubes next to the metal electrodes, and can be discharged whenever the electricity is needed.

Postdoctoral students Dan Zhao and Hui Wang, and doctoral student Zia Ullah Khan, found the right polymers after years of fruitless experiments. They produced an electrolyte with 100 times greater ability to convert heat to electricity than the electrolytes normally used.

Professor Xavier Crispin said, “We still don’t know exactly why we’re getting this effect. But the fact is that we can convert and store 2,500 times more energy than the best of today’s supercondensers linked to thermoelectric generators.”

The electrolyte contains only non-hazardous, simple, and cheap materials that are stable and can be handled at room temperature. The ion-driven thermoelectric supercondenser therefore opens up new possibilities of storing solar electricity, to take one example. The research has resulted in two patents. The team’s hope is that the results will lead to an entirely new type of energy storage that can be mass-produced on an industrial scale.

Thermophoresis in liquid mixtures was first observed and reported by Carl Ludwig in 1856, 160 years ago and has found uses in an array of technologies in manufacturing. But now there is reason to think the rather obscure effect has a mass market use.

A condenser is another useful segment of the electrical energy storage field of batteries and capacitors. If the technology can charge, without the heat being converted to electricity first, the efficiency potential could be quite high indeed.


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