Electrocaloric cooling technologies, enabled by the discovery of the giant electrocaloric effect in dielectrics more than a decade ago, represents a zero-global-warming-potential, environment-benign cooling alternative. Benefited from its nature as an electricity-driven capacitor, the electrocaloric working body renders the great advantages in the energy efficiency and the device integration. The decade-long efforts on advancing the technology revealed many promising material candidates with matured manufacturing protocols, as well as intriguing device prototypes for applications beyond the traditional vapor compression based cooling. This article presents the recent advances in electrocaloric cooling technologies, from material improvements to device demonstrations. The environmental impact and the energy efficiency of the technology were evaluated by the total effective warming impact and the material COP, respectively. In addition to the current progresses achieved by the decade-long research effort, the existing challenges and potential opportunities brought by the electrocaloric refrigeration will be discussed. In general, applying or removing an external work to a refrigerant can cause a reversible phase transition with heat ejection or absorption. Various thermodynamic cycles based on the liquid-gaseous phase transition are where the foundation of conventional vapor compression refrigeration (VCR) was built on. Analogous to the VCR, the electrocaloric refrigeration (ECR) utilizes an electric field to induce a dipolar order-disorder phase transition where a reversible temperature change enables the heat pumping. The discovery of the giant electrocaloric effect (ECE) in solid-state materials a decade ago quickly revived the interests on the ECR from both academia and industrial. Numerous advances have been achieved in condensed matter physics, from normal FE to relaxor FE and from solid-state dielectrics to fluidic dielectrics. The ECE-induced temperature changes exceeded 30 K under high external electric fields. The ECR is environmentally benign. Operating a solid-state or condensed matter cooling agent, ECR emits no harmful gas directly, such as gases with ozone depletion potential (ODP) and/or global warming potential (GWP). The electrocaloric (EC) materials hold the promise of high energy efficiency because of their nature as low-loss insulators. Overall, our review shows that the ECR exhibits an incredibly low total equivalent warming impact (TEWI), with both direct and indirect equivalent CO2 emission considered. EC cooling devices have been demonstrated by researchers in university research groups as well as in R&D centers of industrial cooperation that are pioneering in the field. The uniqueness of the EC working bodies, i.e., compressor-free, low-noise, high-efficiency, flexibility, scalability, optic transparency, electromechanical maneuverability, etc., may extend the ECR to new application scenarios beyond the traditional household refrigeration and air conditioners. Future advances of the ECR could lead to point-of-care, distributive thermal management, on-chip cooling, wearable thermal management, and highly efficient climate-controlling systems for electric vehicles. The development of this interdisciplinary field calls for in-depth collaboration among research societies of condensed matter physics, material engineering, mechanical and thermal engineering, refrigeration and cryogenics, and industrial manufacturing. The global climate shift calls for a series of technical innovations that exhibit low-carbon-emission over their lifetimes. The discovery of the giant electrocaloric effect (ECE) stimulated a new research field of the environmental-benign, high-efficiency cooling technology, which extends the boundary of the conventional refrigeration as well as the condensed matter physics. In this review, we summarize the major advances of the ECE in the fundamental physics, materials, devices demos, and the state of arts over the last decade. Challenges, opportunities, and perspectives of the future development of the rejuvenated research field are discussed.
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