Competitive cooling with capacitors: Current large-scale cooling devices use vapor compression refrigeration. The efficiency of air conditioners has been optimized, but they can be noisy and rely on problematic greenhouse gases. Two groups now present designs for electrocaloric cooling using lead scandium tantalate capacitors that change temperature under an electric field. Y. Wang et al. obtained a very large heat flux using only solid materials and a cooling fan to remove heat from their device. Torello et al. used fluids for heat transfer, leading to a very large temperature difference between the hot side and the cold side. The new designs demonstrate the potential for devices that might be competitive with vapor compression–based appliances with further optimization. Science , this issue p. 129 , p. 125

Cooling through solid-state electrocaloric materials is an attractive replacement for vapor compression. Despite recent efforts, devices that are potentially commercially competitive have not been developed. We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 2.1 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown. Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 54% of Carnot’s efficiency as long as energy is properly recovered. We believe that this demonstration shows electrocaloric cooling to be a very promising alternative to vapor compression cooling.

Materials that show large and reversible electrically driven thermal changes near phase transitions have been proposed for cooling applications, but energy efficiency has barely been explored. Here we reveal that most of the work done to drive representative electrocaloric cycles does not pump heat and may therefore be recovered. Initially, we recover 75–80% of the work done each time BaTiO₃-based multilayer capacitors drive electrocaloric effects in each other via an inductor (diodes prevent electrical resonance while heat flows after each charge transfer). For a prototype refrigerator with 24 such capacitors, recovering 65% of the work done to drive electrocaloric effects increases the coefficient of performance by a factor of 2.9. The coefficient of performance is subsequently increased by reducing the pumped heat and recovering more work. Our strategy mitigates the advantage held by magnetocaloric prototypes that exploit automatic energy recovery, and should be mandatory in future electrocaloric cooling devices.

Since the discovery of giant electrocaloric effects, researchers are intensively studying electrocaloric cooling as an alternative to vapor compression systems to develop more efficient heat pumps and mitigate climate change. Endorsed by its direct use of electricity, easy‐handling, and compact design, recent advancements in the performance of electrocaloric coolers have finally displayed temperatures comparable to similar competing technologies, and the topic has regained attention and interest. In this work, the design, performance, and working principles of all electrocaloric prototypes before the year 2021 are reviewed, and hints and guidelines are given for future works to bring the development of these devices one step closer to real applications.

Coming up with sustainable sources of electricity is one of the grand challenges of this century. The research field of materials for energy harvesting stems from this motivation, including thermoelectrics¹, photovoltaics² and thermophotovoltaics³. Pyroelectric materials, converting temperature periodic variations in electricity, have been considered as sensors⁴ and energy harvesters^5–7, although we lack materials and devices able to harvest in the joule range. Here we develop a macroscopic thermal energy harvester made of 42 g of lead scandium tantalate in the form of multilayer capacitors that produces 11.2 J of electricity per thermodynamic cycle. Each pyroelectric module can generate up to 4.43 J cm⁻³ of electric energy density per cycle. We also show that two of these modules weighing 0.3 g are sufficient to sustainably supply an autonomous energy harvester embedding microcontrollers and temperature sensors. Finally, we show that for a 10 K temperature span these multilayer capacitors can reach 40% of Carnot efficiency. These performances stem from (1) a ferroelectric phase transition enabling large efficiency, (2) low leakage current preventing losses and (3) high breakdown voltage. These macroscopic, scalable and highly efficient pyroelectric energy harvesters enable the reconsideration of the production of electricity from heat.

Electrocaloric materials are promising working bodies for caloric-based technologies, suggested as an efficient alternative to the vapor compression systems. However, their materials efficiency defined as the ratio of the exchangeable electrocaloric heat to the work needed to trigger this heat remains unknown. Here, we show by direct measurements of heat and electrical work that a highly ordered bulk lead scandium tantalate can exchange more than a hundred times more electrocaloric heat than the work needed to trigger it. Besides, our material exhibits a maximum adiabatic temperature change of 3.7 K at an electric field of 40 kV cm⁻¹. These features are strong assets in favor of electrocaloric materials for future cooling devices.