Researchers at the University of Tsukuba in Japan have developed a thermocell containing a material that exhibited a temperature-induced phase transition of its crystal structure. Just above room temperature, the atoms in this solid material rearranged to form a different crystal structure. This phase transition resulted in an increase in output voltage from zero to around 120 mV, representing a considerable performance boost compared to existing thermocells.
“The temperature-induced phase transition of our material caused its volume to increase,” said Professor Yutaka Moritomo, senior author of the study. “This in turn raised the output voltage of the thermocell.”
The researchers were able to finely tune the phase transition temperature of their material so that it lay just above room temperature. When a thermocell containing this material was heated above this temperature, the phase transition of the material was induced, which led to a substantial rise of the output voltage from zero at low temperature to around 120 mV at 50 °C.
As well as tackling the problem of low output voltage, the thermocell containing the phase transition material also overcame the issue of a temperature-dependent output voltage. Because the increase of the output voltage of the thermocell induced by the thermal phase transition was much larger than the temperature-dependent fluctuations of output voltage, these fluctuations could be ignored.
“Our results suggest that thermocell performance can be strongly boosted by including a material that exhibits a phase transition at a suitable temperature,” said Moritomo. “This concept is an attractive way to realize more efficient energy-harvesting devices.”
The research team’s design combining thermocell technology with an appropriately matched phase transition material leads to increased ability to harvest waste heat to power electronics and has potential for providing independent power supplies for advanced electronics they say.
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