Brief introduction to electrocaloric cooling and pyroelectric energy harvesting

Authors: ULJ team

Electrocaloric and pyroelectric effects illustrate how certain solid-state materials can convert between thermal and electrical energy. These phenomena are essentially inverse: applying an electric field can produce a temperature change (electrocaloric effect), while a temperature change can induce an electric charge (pyroelectric effect). Both are being explored for their potential to revolutionize cooling and heat pumping, as well as energy harvesting technologies; especially given that nearly half of global energy use (and ~40% of CO₂ emissions) comes from heating and cooling.

Figure 1 schematically represents the two processes.

Figure 1. Left: Typical cooling or heat pump cycle. Right: typical power generation (energy harvesting) cycle. The alternating electric field E is coupled with heat transfer process in the thermodynamic cycle, where W  is input energy (other than heat) and the arrows inside of material represent the orientation of electric dipoles. Figure is reproduced from Ref. ¹

The electrocaloric effect is observed in ferroelectric ceramics and polymers, where an electric field induces a reversible temperature and entropy change. In essence, applying a field aligns electric dipoles and releases heat (material warms up), and removing the field causes the material to absorb heat and cool down. By cycling an electric field, this effect can be used in a heat pump or refrigerator. Electrocaloric cooling needs no compressors or refrigerant gases – resulting devices are compact, quiet, and emit zero greenhouse gases. Recent research has greatly improved this technology: for example, a 2023 electrocaloric prototype achieved a 20.9 K temperature span and 2.1 W of cooling power under a moderate 10 V/μm field, reaching about 54% of Carnot efficiency with energy recovery. ² Such performance suggests solid-state electrocaloric coolers could become a competitive, eco-friendly alternative to conventional vapor-compression systems.

Conversely, pyroelectric materials generate an electric current or voltage when their temperature changes. Today, there is growing interest in pyroelectric energy harvesting, which uses cyclic temperature swings (from waste heat or environmental variations) to produce electricity. A state-of-the-art demonstration in 2022 used multilayer lead–scandium–tantalate capacitors (~42 g of material) to generate 11.2 J of electricity per cycle – an energy density of 4.43 J/cm³ – and achieved ~40% of Carnot efficiency for a 10 K heat span.³ Remarkably, just two of these small pyroelectric modules (0.3 g total) could continuously power a microcontroller and sensors, showing the feasibility of powering IoT devices or reclaiming industrial waste heat via pyroelectric harvesters.

THERMINATOR project

In this project, we will combine two technologies — electrocaloric (pyroelectric) and thermoacoustic energy conversion — to achieve efficient, high-power energy generation that outperforms each technology used independently.

References

1. Klinar, K., Law, J. Y., Franco, V., Moya, X. & Kitanovski, A. Perspectives and Energy Applications of Magnetocaloric, Pyromagnetic, Electrocaloric, and Pyroelectric Materials. Adv Energy Mater 14, (2024).
2. Li, J. et al. High cooling performance in a double-loop electrocaloric heat pump. Science (1979) 382, 801–805 (2023).
3. Lheritier, P. et al. Large harvested energy with non-linear pyroelectric modules. Nature 609, 718–721 (2022).