Pyro-brainiacs set new record with waste-heat-into-electricity study

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Californian scientists have come up with a way of converting waste heat from electronics back into electricity with improved efficiency, according to a study in Nature Materials.

The system uses a process called pyroelectric energy conversion, which the study shows can take low-quality waste heat (which it might interest you to know is anything below 100˚C) and turn it into electricity thanks to the relaxor ferroelectric film created by the scientists.

Neither the process nor the material is particularly new. The innovation is in the thin film.

Pyroelectricity is the ability of certain materials to generate a charge when heated or cooled, and was first noted in Greek philosopher Theophrastus's On Stones, written almost 2,500 years ago. The effect did not acquire today's name until David Brewster used the term in his paper entitled "Observations on the pyro-electricity of minerals".

Towards the end of the 20th century, pyroelectric elements were found to be useful for thermal imaging both on Earth and in space.

Relaxor ferroelectrics have been around for 50 years, and the team synthesised a thin-film version of the material at a thickness of 50- 100 nanometers.

The Berkeley-based team then fabricated a pyroelectric structure based on the film and tested the machine's power generation capabilities. The device set new records for pyroelectric energy conversion with a maximum energy density of 1.06 Joule cm³, power density of 526 Watts cm³, and a Carnot efficiency of 19 per cent.

Lane Martin, senior author of the paper and associate professor of materials science and engineering at Berkeley, said: "We know we need new energy sources, but we also need to do better at utilizing the energy we already have... These thin films can help us squeeze more energy than we do today out of every source of energy."

While the study has helped demystify the properties of pyroelectric physics, further work is needed to get the film optimised for specific heat streams and temperatures. ®

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