3D Printing Architecting β-PVDF Reservoirs for Preferential ZnO Epitaxial Growth Toward Advanced Piezoelectric Energy Harvesting.

For polyvinylidene fluoride (PVDF) based piezoelectric composites, epitaxial growth of ZnO nanorods (ZnO-nr) piezoceramic layer on PVDF is an effective way to improve their piezoelectric performance. However, the crystal nucleus of ZnO featuring polar surfaces that cannot be directly attached to hydrophobic PVDF with low surface energy. Herein, direct ink writing (DIW) 3D printing is employed for the first time to create β-PVDF reservoirs with significantly enhanced surface energy, facilitating the attachment and epitaxial growth of ZnO-nr. The printed β-PVDF reservoirs designed with programmed macro-pores and abundant inner micropores, enable a higher loading of ZnO-nr by more than one magnitude, thereby boosting the electro-mechanical response. The resulting PVDF/ZnO core-shell piezoelectric energy harvester (PEH) delivers an output voltage of 33.2 V, as well as an unprecedentedly high relative output voltage of 2.76 V/wt.%, which is 2.63 times that of the state-of-the-art 3D-printed PVDF/piezoceramics PEHs. Furthermore, it can differentiate subtle human motions whereas hybrid PEHs cannot distinct. This work demonstrates that the DIW 3D printing approach offers a simple and convenient design idea for creating high performance PEHs.