On December 1, the research group of Professor Qian Xiaoshi of the Prospective Interdisciplinary Research Center of the School of Mechanical and Power Engineering of Shanghai Jiao Tong University published "Colossal Electrocaloric Effect in an Interface-augmented Ferroelectric Polymer" in Science. The extensive formation of the polarization interface of the polymer is induced by the sacrificial layer of the small molecule crystal, which makes the ferroelectric polymer exhibit a huge entropy change under the action of the external electric field, realizes the Pondian card effect in the traditional vinylidene fluoride relaxation ferroelectric polymer, and reveals the entropy change mechanism of the polarization interface of topological epitaxy under the control of the external electric field. Professor Qian Xiaoshi is the sole corresponding author of this paper, and doctoral student Zheng Shanyu is the first author. This is the second time that Qian's research group has published in Science as the first author this year.
science · 30 nov 2023 · vol 382, issue 6674
The giant electro-card effect is a peculiar condensed matter physical phenomenon, which uses the refrigeration cycle composed of alternating polarization-depolarization during the charging and discharging of solid dielectrics to produce reversible electro-temperature changes. The electric card refrigeration system has the characteristics of low power loss, high energy efficiency, zero greenhouse effect potential, easy miniaturization and lightweight, etc., which provides one of the important disruptive forward-looking technologies for the replacement of refrigerants and the realization of the dual carbon goal。By reducing the polar domain size of the relaxation body, the dipole flip energy barrier between the two polar entropy states can be reduced, thereby increasing the electric field-induced dipole entropy change. The reported domain sizes are all 100-20 nm, but further reducing the domain size to the sub-nanometer scale is challenging due to the complex crystallization process of the relaxed ferroelectric.
After the polar interface is formed, the small molecule crystals can volatilize away from the polymer network at high temperature, so as not to affect other electrical properties of the polymer, and a large number of small and large sub-nanometer cavities and polar interfaces are cleverly introduced to improve the entropy change of the material. At a low electric field of 20% breakdown, the entropy changes to 100 j (kg.).k) It is 4 times that of ordinary polymers, and the strength of the electrical card is more than 1 j (kg.).k.MV), with a refrigeration capacity of 5x103 J kg and a stable operation of 3 million cycles
DMHD molecule-induced polymer interface enhancement showed giant electric card performance.
The use of nano-infrared technology showed that a large number of polar conformations were retained at the nanopore interface, and all of them appeared at the edge of the grain. The dense sub-nanometer two-dimensional polar interface replaces the three-dimensional polar nanodomain region at the hundred-nanometer scale, and becomes the main contributor to the electrical card effect.
Interface-enhanced IR-PIFM characterization of polar and non-polar conformations.
Photoluminescent infrared hyperspectroscopy (HYPIR) was used to acquire infrared absorption chemical images in the spectral range of 1600-780 cm-1 of electric card polymers. TPD not only exhibits obvious interfacial all-transpolar conformational enhancement signals, but also forms more polymer conformational types, which has stronger multiphase coexistence characteristics.
Structural analysis of interface-enhanced polymers and common polymers.
In situ WAXD studies the dynamic transition of the three-dimensional bulk crystal structure under the action of electric field, and DMHD induces a strong phase transition in the substrate polymer. DFT and MD models also intuitively show that the non-polar to polar phase transition barrier can be reduced due to the presence of interfacial hydrogen bond interactions. The elastic neutron scattering results show that the mean square displacement of TPD-UN before annealing is the smallest, indicating that hydrogen ions are tightly confined near the surface of small molecules, and the constraints of the polar conformational interface with large surface area can be released by sacrificing DMHD, which promotes the giant electro-clamp effect of TPD.
Dielectric behavior and cycling properties of modified polymers.
The landau-ginzburg-devonshire thermodynamic model was used, supplemented by the phase field simulation experimental results. Through the dielectric property analysis, the improvement of polarization strength and dielectric constant confirmed the existence of interface-enhanced electrical card effect materials。The nanoporous polar interface is exposed to a free volume that is not physically constrained, unlike the adverse complications associated with permanent composite fillers.
The TPD jumbo effect has good temperature stability around room temperature and can cover an effective temperature window of 10 to 70. The refrigeration efficiency of COPMat is up to 250% higher than that of ordinary polymers, and the stability cycle test is up to 3 million cycles。This further reduces the size and weight of the power supply, powering potential portable card cooling.
This is the first time that a domestic university has published a study on the theme of electric card refrigeration in science with the first author's unit**。**The research work was supported by several teams, among which the quasi-elastic neutron scattering experiment was completed by the team of Hong Liang from the School of Physics, Shanghai Jiao Tong University; Professor Jiangping Chen from the School of Mechanical Power, Houbing Huang's team at Beijing Institute of Technology, and Yurong Yang's team from Nanjing University provided important support for this research. In addition, Molecular Vista and Bruker (Beijing) are also involved in research on nano-infrared.
The research work has been funded by the Ministry of Science and Technology's Key R&D Program of Transformative Technologies and Key Scientific Problems, the National Natural Science Program and the Shanghai Natural Science Original Exploration Project, the National Key Laboratory of Mechanical Systems and Vibration Project, the "Deep Blue Plan" project of Shanghai Jiao Tong University and the "Key Forward-looking Layout" project. The Student Innovation Center and Analysis and Testing Center of Shanghai Jiao Tong University, the Shanghai Synchrotron Radiation Light Source BL19U2 and BL16B1 Line Stations, and the Australian Nuclear Science and Technology Center provided experimental resources for the research work.
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*: Faculty of Mechanical and Power Engineering.
Editor-in-charge: Member of the "Four Forces" Co-operation Program.
Smart Energy Innovation Institute Lai Siyang.
Editor-in-Chief: Jin Xue.
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