Metal-organic frameworks Co3[Co(CN)6]2: A promising candidate for dramatically reinforcing the piezoelectric activity of PVDF

Over decades, the exploration of poly(vinylidene fluoride) (PVDF) based composites with outstanding piezoelectric activity has gained great popularity and interest from diverse research communities because of their potential in realizing flexible sensors and energy harvesters. Herein, in this work, we reported a novel high performance PVDF based piezoelectric composites containing Metal-organic frameworks (MOF) Co3[Co(CN)6]2. The ultra-high specific surface area and unique open framework nanostructure of Co3[Co(CN)6]2 demonstrated to be efficient in inducing strong interfacial coupling effect within PVDF, resulting in piezoelectricity enhancement. Moreover, the redox behavior of metal ions in Co3[Co(CN)6]2 which provides pathway for electrons, was anticipated to further hardness the interfacial coupling effect and consequently piezoelectric reinforcing effect. Upon an addition of 0.6 wt% Co3[Co(CN)6]2, the piezoelectric response of composites reached the maximum, i.e. a d33 and a d31 of 37 pC/N and 33 pC/N, respectively, which are both almost double those of PVDF. Furthermore, the resultant composites exhibited superior electromechanical coupling factor k31 up to 0.135 while that of pure PVDF was only 0.078. For the first time, we present the applicability of MOF as a new class of reinforcing fillers for piezoelectric composites, providing a new perspective to develop PVDF based composites with superior piezoelectric response.