Flexible magnetocaloric fiber mats for room-temperature energy applications

Abstract

Currently, magnetocaloric refrigeration technologies are emerging as ecofriendly and more energy-efficient alternatives to conventional expansion-compression systems. However, major challenges remain. A particular concern is the mechanical properties of magnetocaloric materials, namely, their fatigue under cycling and difficulty in processing and shaping. Nevertheless, in the past few years, using multistimuli thermodynamic cycles with multicaloric refrigerants has led to higher heat-pumping efficiencies. To address simultaneously the challenges and develop a multicaloric material, in this work, we have prepared magnetocaloric-based flexible composite mats composed of micrometric electroactive (EA) polyvinylidene fluoride (PVDF) fibers with embedded magnetocaloric/strictive La(Fe,Si)<inf>13</inf> particles by the simple and cost-effective electrospinning technique. The composite’s structural characterization, using X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and measurements of the local-scale piezoresponse, revealed a cubic NaZn<inf>13</inf>-type structure of the La(Fe,Si)<inf>13</inf> phase and the formation of the dominant polar β-phase of the PVDF polymer. The PVDF-La(Fe,Si)<inf>13</inf> composite showed an enhancement of the longitudinal piezoelectric coefficient (effective d<inf>33</inf>) (−11.01 pm/V) compared with the single PVDF fiber matrix (−9.36 pm/V). The main magnetic properties of La(Fe,Si)<inf>13</inf> powder were retained in the PVDF-La(Fe,Si)<inf>13</inf> composite, including its giant magnetocaloric effect. By retaining the unique magnetic properties of La(Fe,Si)<inf>13</inf> embedded in the electroactive piezoelectric polymer fiber mats, we have designed a flexible, easily shapeable, and multifunctional composite enabling its potential application in multicaloric heat-pumping devices and other sensing and actuating devices.