BCZT-based Lead-free Piezoceramics For Human Body Kinetic Energy Harvesting

As one of the abundant green energy sources,human kinetic energy has attracted considerable attention due to the rapid development of piezoelectric energy harvesters(piezoelectric nanogenerators,PENG)and wearable electronics.Over the decades,PZT has dominated the application market of piezoelectric electronic devices,but its high lead content has caused huge harm to human and the environment.In view of the high piezoelectricity that is comparable to PZT and the lead-free property of BCZT,developing environment-friendly flexible lead-free BCZT piezoelectric ceramic films to harvest human kinetic energy is of great significance for the effective utilization of clean energy and the practical use in wearable electronics.Considering the high lead toxicity of PZT and the unable use of traditional lead-free BCZT piezoceramics in wearable electronics,an AB-site ion co-doping idea is proposed,which balances the sintering,phase transition and electrical properties of BCZT-based lead-free piezoceramics.The fabricated BCZT ceramic fibers or films can effectively harvest human kinetic energy,indicating the established application bridge between rigid ceramics and flexible electronics.Moreover,flexible hybrid devices based on piezoelectric and triboelectric effects(PTNG)are developed,which not only improves the output and sensitivity to human minute motions,but also demonstrates the great potential use in wearable electronics.The innovative results are as follows(1)Cu2+ and Y3+were doped to the AB site of BCZT structure,and the impacts of Cu/Y doping on the sintering,phase transition and electrical properties of BCZT system were studied.It is found that the improvement of sintering and phase transition properties is attributed to the formation of oxygen vacancies accelerating mass transfer and the tolerance effect of Cu/Y,respectively.While the significant improvement of electrical properties results from the donor doping effect of Y3+,the intensified domain well motion,as well as the enhanced charge transfer among piezoelectric particles.Therefore,the balance between sintering,phase transition and electrical properties of BCZT-based lead-free piezoceramics is achieved,and a plausible mechanism is obtained to explain the role of Cu/Y in the formation of BCZT solid phase structure(2)In order to establish the application bridge between rigid ceramics and flexible electronics,piezoelectric composite films based on BCZT-CuY ceramic powders were fabricated,and the promiting effect of rGO on the dispersion of BCZT-CuY and the mechanical and electrical properties of its composite films were explored.It is confirmed that not only can the covalent bond effect between rGO and PDMS compensate for the mechanical loss of the composite film caused by BCZT-CuY addition,but also rGO acts as dispersing and conducting agents to make BCZT particles uniformly distributing in PDMS,and further to enhance the electrical properties of the composite film.With the input of minute human kinetic energy by finger tapping,BCZT-CuY/rGO PENG shows good output,indicating its application prospects in flexible electronics.(3)In term of the high sintering temperature and low content of the above films,uniaxially aligned BCZT ceramic nanofibers were synthesized by electrospinning,and the impacts of fiber alignment and Y doping on the physical and electrical properties were investigated.The low-temperature sintering property and high Curie temperature of BCZTY NFs are ascribed to the low reaction barrier of the intermediate products and the discontinuous physical properties of the nanofibers,respectively.While the donor doping effect of Y element and the electric field along with NFs alignment orientations are two main factors contributing to the enhancement of electrical performance.Compared with BCZT-CuY/rGO PENG,BCZTY-NF PENG can more efficiently harvest human kinetic energy driven by finger tapping(4)Considering the limited flexibility and output of the above naonfibers,electrospun composite ceramic fibers were developed by combining highly flexible PVDF-HFP and highly piezoelectric BCZT,and the structure-function relationship between different nanofibers obtained by different methods and electrical properties was systemactically studied.It is observed that BCZT nanoparticles prepared by the sol-gel method can be uniformly dispersed on the PVDF-HFP NFs surface,which significantly improves both piezoelectric and triboelectric output of BP-SG PTNG Owing to the rough surface of BP-SG NFs and the small inter-fiber distance between these NFs,the spacer-free BP-SG PTNG in both single-electrode and two-electrode modes exhibits high sensitivity to hand motions.(5)To further optimize the structure and output of BCZT-based PTNG,spacer-free GO LS-TENG was fabricated using GO dispersion and BCZT-CuY/PDMS as liquid electrode and piezo-triboelectric material,respectively,and the role of GO in the liquid and output was discussed.It is clarified that a proper amount of GO addition can promote the formation of single or several layers of charge channel in the liquid,which benefits the improvements of charge transfer and output performance.Given that the triboelectric output is much higher than the piezoelectric output,the optimal power density of pure GO LS-TENG achieves 4.97 W/m2.This device can effectively harvest human kinetic energy based on skin,clothing and metal,indicating its huge potential applications in wearable electronics.