Self-oscillating polymeric refrigerator with high energy efficiency

Electrocaloric^1,2 and electrostrictive^3,4 effects concurrently exist in dielectric materials. Combining these two effects could achieve the lightweight, compact localized thermal management that is promised by electrocaloric refrigeration⁵. Despite a handful of numerical models and schematic presentations^6,7, current electrocaloric refrigerators still rely on external accessories to drive the working bodies^8-10 and hence result in a low device-level cooling power density and coefficient of performance (COP). Here we report an electrocaloric thin-film device that uses the electro-thermomechanical synergy provided by polymeric ferroelectrics. Under one-time a.c. electric stimulation, the device is thermally and mechanically cycled by the working body itself, resulting in an external-driver-free, self-cycling, soft refrigerator. The prototype offers a directly measured cooling power density of 6.5 W g^-1 and a peak COP exceeding 58 under a zero temperature span. Being merely a 30-µm-thick polymer film, the device achieved a COP close to 24 under a 4 K temperature span in an open ambient environment (32% thermodynamic efficiency). Compared with passive cooling, the thin-film refrigerator could immediately induce an additional 17.5 K temperature drop against an electronic chip. The soft, polymeric refrigerator can sense, actuate and pump heat to provide automatic localized thermal management.