A Chinese research team has developed a new concept to extract thermal energy from low-temperature waste heat sources and reuse it as needed simply by controlling the pressure. Heat generation accounts for more than 50% of the world’s final energy consumption, and the waste heat potential analysis shows that 72% of the world’s primary energy consumption is lost after conversion, mainly in the form of heat. It is also responsible for more than 30% of global greenhouse gas emissions.

Against this background, researchers led by Professor LI Bing from the Metal Research Institute of the Chinese Academy of Sciences have proposed and implemented a new concept – barocaloric thermal batteries, based on a unique reverse barocaloric effect.

The reverse barocaloric effect is characterized by a pressure-dependent endothermic reaction, which is the opposite of the traditional barocaloric effect, in which an increase in pressure leads to an exothermic reaction. “The cycle of a barocaloric thermal battery consists of three stages, including thermal charging under pressure, storage under pressure, and thermal discharge after depressurization,” said Professor LI, the study’s corresponding author.

Barocaloric thermal battery, ammonium thiocyanate (NH₄ SCN). The discharge manifested itself as 43 J/ heat release.^Mr or about 15 K increase in temperature. The heat released was 11 times greater than the mechanical energy supplied.

Working material NH to understand the physical origin of the unique reverse barocaloric effect₄ The SCN is well characterized by synchrotron X-ray and neutron scattering techniques. It undergoes a crystalline structural phase transition from monoclinic to orthorhombic phase at 363 K, accompanied by a volumetric negative thermal expansion of ~5% and entropy changes of about 128 J kg. ^-one K ^-one.

This transition is easily accomplished at pressures up to 40 MPa and is the first reverse barocaloric system with entropy changes greater than 100 J kg. ^-one K^–. Pressure-dependent neutron scattering and molecular dynamics simulations showed that the transverse vibrations of SCN¯ anions increase with pressure and the hydrogen bonds forming the long-range order subsequently weaken.

As a result, the system becomes disordered in response to external pressure and thus the material draws heat from the environment. As a new solution for thermal management, barocaloric thermal batteries are expected to play an active role in a variety of applications such as low temperature industrial waste heat collection and reuse, solid state cold heat transfer systems, smart grids and residential thermal. to manage.