Abstract
Electrocaloric1,2 and electrostrictive3,4 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 presentations6,7, current electrocaloric refrigerators still rely on external accessories to drive the working bodies8,9,10 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.
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Data availability
All data generated or analysed during this study are included in the paper, the Extended Data and the Supplementary Information, and are also available from the corresponding authors upon request. Source data are provided with this paper.
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Acknowledgements
This work was supported by the National Key R&D Program of China (2020YFA0711500, 2020YFA0711503), the National Natural Science Foundation of China (52076127) and the Natural Science Foundation of Shanghai (20ZR1471700, 22JC1401800). X.Q. expresses thanks for the support by the State Key Laboratory of Mechanical System and Vibration (Grants No. MSVZD202211 and No. MSVZD202301), the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University (Project No. SL2020MS009), the Prospective Research Program at Shanghai Jiao Tong University (19X160010008) and the support of the Shanghai Jiao Tong University 2030 Initiative. We thank Luology (Shandong) Advanced Equipment Technology Co., Ltd for support with contact thermal resistance tests. We thank S. Lin for his support with the simulation software. We express thanks for the support by the Student Innovation Center, the Instrumental Analysis Center at Shanghai Jiao Tong University and the National Facility for Translational Medicine (Shanghai).
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Contributions
X.Q. conceived the concept, designed the device and wrote the manuscript. X.Q., D.H. and Y.Z. conducted the experiments for device performance characterization and reviewed the manuscript. D.H. and S.Z. carried out the materials. C.H. and X.C. measured the strain–electric field curves. D.H., Q.L. and F.D. carried out the simulation. Y.Z. and J.S. supervised the thermal resistance tests. X.Q., D.H. and Y.Z. took the device pictures. D.H., D.W. and Y.Z. designed the energy recovery circuit. H.D., W.C. and G.L. sputtered the electrodes. D.H. and F.D. designed the controlling logical models. X.Q. and J.C. administrated the project. X.Q. supervised the project. All authors analysed and interpreted the data.
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X.Q., D.H., Q.L. and Y.Z. are inventors on a patent application related to the described work. The other authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Comparison between the measured temperatures from the infrared camera under various emissivity.
a, Temperature images provided by the IR camera, in which the circle areas are effective for 0.2 and 0.4 emissivity. b, Comparison of temperature data acquired by thermocouple (grey dot line) and IR camera (dots, with light blue line for guidance) at different surrounding temperatures.
Extended Data Fig. 2 Calibration process for heat flux sensor.
a, System designed for measuring cooling power, with a calibration resistance and a sensor signal amplifier. b, Heat loss is caused by foam covering the surface of the resistance in the calibration process. c, Heat loss is caused by air convection on the surface of the DMP film in the practical testing process. d and f, Heat flux signal changing with time until stability as the resistance was heated with foam (d) and air convection (f). e and g, Linear fitting results showing the correlation coefficients with foam (e) and air convection (g).
Extended Data Fig. 3 Measurement of bouncing heights of the DMP and the base terpolymer.
a, View of the camera, in which the 1 mm PP sheet was used as a reference. b, Measured heights of the terpolymer and the DMP under various electric fields.
Extended Data Fig. 4 Bouncing heights have a significant impact on the leakage between the heat source and the heat sink.
a, Heat leakage signals of the device due to the low hGap ~ 0.6 mm. b, As reducing the hGap of the DMP device to ~ 0.6 mm, the heat leakage signals are enhanced.
Extended Data Fig. 5 Long-time operation performance tests.
a, Cooling signal comparison of TD-0.6% at initial and after 1,000,000 cycles. b, Entropy changes of TD-0.6% at initial and after 61,200 cycles. c, Heat flux density curves of the device at initial, after 23,100 cycles, and after 70,800 cycles. d, Comparison of average cooling power densities corresponding to different cycles.
Extended Data Fig. 6 Applied voltage and fluxing charge measurements.
a, Circuit designed to measure fluxing charges through the device. b, Measured current through and voltage on the device.
Extended Data Fig. 7 Simulation for energy recovery between two devices utilizing a circuit with an inductance.
a, Circuit designed to recover the discharging energy. b, Voltage changes of 2 DMP films with time. c, An enlarged view of (b) at around 1 s showing that the recovering process is less than one microsecond.
Extended Data Fig. 8 On/off control by measuring the capacity of the DMP film.
In the on/off control cycle, a micro-computer continuously monitors the dielectric constant of the DMP film. The dielectric constant at a reference temperature of 30 °C serves as the baseline. Simultaneously, the real-time dielectric constant is calculated from the capacitance measurements obtained using an LCR metre. When the real-time dielectric constant exceeds the reference value, the system triggers the high voltage amplifier that then applies AC high voltages to the DMP film.
Supplementary information
Supplementary Information
This file contains Supplementary Figs. 1–10, Tables 1–3 and Notes 1 and 2.
Supplementary Video 1
Motion of the DMP film. When the DMP film was sandwiched between the hot and cold ends, we could not clearly observe the motion of the DMP film. To clearly capture the motion from the top view, we removed the hot and cold ends and allowed the DMP film to bounce freely. The video shows the DMP film powered by a voltage of 2 kV at an operating frequency of 0.5 Hz.
Supplementary Video 2
A 3 × 3 fridge array. Arrays of electrodes with millimetre scales could be designed to meet the cooling needs of surfaces with uneven heat distribution. This video demonstrates a 3 × 3 array circuit in which each unit could be driven on its own by controlling the specified voltage and operating frequency. Gold electrodes with specific shapes were sputtered onto two surfaces of the DMP film. The lower electrodes of all these units were grounded for insulation, and the upper electrodes were connected to different high-voltage outputs through the sputtered gold wires on the upper surface. The effective working area for one unit was the 1 mm × 1 mm square overlapped by the upper and lower surface electrodes. In this demonstration, two units (row 1, column 3 and row 2, column 1) were powered simultaneously at 2 kV and 0.5 Hz, and one unit (row 1, column 1) was powered by an independent voltage at 1.5 kV and 1 Hz.
Supplementary Video 3
Demonstration for automatic temperature regulation. In this video, our device was attached to a temperature soaking plate on PCB, and a transparent quartz glass was placed above, serving as the heat sink. With the capacity of the DMP film detected, the applied voltage was adjusted in real time. Once the perceived temperature exceeded 30 °C, the device started to work, and the frequency accelerated as the temperature increased. The device would stop working as the perceived temperature dropped below 30 °C.
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Han, D., Zhang, Y., Huang, C. et al. Self-oscillating polymeric refrigerator with high energy efficiency. Nature (2024). https://doi.org/10.1038/s41586-024-07375-3
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DOI: https://doi.org/10.1038/s41586-024-07375-3
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