BSZT/BNNS-Incorporated PVDF Composites for Dramatically Enhanced Electrocaloric Cooling Capability

With increasing global concerns over energy efficiency and environmental protection, traditional refrigeration technologies encounter significant challenges. The electrocaloric effect (ECE), as a solid-state and environmentally friendly refrigeration technology, has emerged a key focus for next-generation cooling devices owing to its ease of control and broad applicability. However, low thermal conductivity (κ < 0.2 W/(m·K)) and high electric field requirements (>100 MV/m) limit its practical application. Herein, we propose a dual-filler synergy strategy by integrating barium strontium zirconium titanate (BSZT) nanofibers (high polarization) and hydroxylated boron nitride nanosheets (BNNSs–OH, high κ and low dielectric constant) into a relaxor ferroelectric polymer matrix. This effectively simultaneously addresses dielectric mismatch and poor thermal management, two long-standing bottlenecks of single-filler ECE systems. The optimized composite (9 wt % BSZT/8 wt % BNNSs) demonstrates outstanding performance at room temperature (30 °C): a significant electrocaloric temperature change (ΔT = 13.5 K at 75 MV/m), enhanced thermal conductivity (κ = 1.6 W/(m·K)), and improved breakdown strength (Eb = 394 MV/m). Compared to the pristine polymer, the composite demonstrates a 230% improvement in cooling efficiency, alongside great cyclic stability over 1000 cycles. This work offers a material-based solution for high-performance solid-state cooling, facilitating practical applications in portable devices, wearable electronics, and chip thermal management.