Ferroelectric Polymer Nanocomposites with Complementary Nanostructured Fillers for Electrocaloric Cooling with High Power Density and Great Efficiency

The exploration of electrocaloric cooling is of great importance to address the environmental and energy efficiency issues in the currently available refrigeration technologies. Although pronounced electrocaloric effect (ECE) has been demonstrated in ferroelectric materials, it is a necessary but far from sufficient condition to achieve substantial cooling. For instance, the narrow operation temperature windows and limited thermal conductivities of ferroelectric materials pose challenging obstacles for ferroelectric materials to realize high cooling power density and great cooling efficiency. In this work, we present polymer nanocomposites with multiple nanostructured fillers, including barium strontium titanate nanowires (BST NWs) with systematically varied Curie temperatures and boron nitride nanosheets (BNNSs). The introduced BST NWs effectively enhance EC strength and significantly extend the operating temperature so that giant ECE is achieved at relatively low electric fields in a wide temperature range. Meanwhile, it is found that BNNSs form an electrically insulating and thermally conductive network in the nanocomposites, resulting in remarkable enhancements in dielectric breakdown strength and thermal conductivity. As validated by the finite element simulations, the synergistic integration of multiple components with complementary functionalities, such as BST NWs and BNNSs, in the ferroelectric polymer renders the nanocomposites with unprecedented high cooling power densities and great cooling efficiencies. Coupled with the facile processability of polymers and lead-free nature of electroactive ceramics, the polymer nanocomposites unleash the immense potential of ECE for environmentally friendly and highly efficient cooling applications.