Toward Balanced Piezoelectric and Mechanical Performance: 3D Printed Polyvinylidene Fluoride/Carbon Nanotube Energy Harvester with Hierarchical Structure

With rapid consumption of fossil energy and its impact on the environment, the desire for clean energy is gradually increasing around the world, and piezoelectric polymers have received extensive attention owing to their capability to harvest discrete mechanical energy in the environment. However, the existing piezoelectric devices are mostly low-dimensional fibers or films, making it difficult to achieve a good balance between mechanical robustness and piezoelectric output. Herein, a polyvinylidene fluoride (PVDF)/multiwalled carbon nanotube (MWCNT) scaffold with a hierarchical porous structure and geometry was fabricated by chemical-foaming-assisted fused deposition modeling (FDM). Chemical foaming was triggered by the heat accompanied during FDM molding, where a microporous structure was formed inside the part without affecting the geometric design to realize strain accumulation in normal space. Moreover, the conductive MWCNT formed discontinuous and parallel morphology around the pores, which not only promotes the polling process and formation of electrets, but also avoids the electrical breakdown caused by the formation of the conductive network. Accordingly, the combined effect of hierarchical structure and incorporation of MWCNT leads to a balanced piezoelectric (open circuit voltage of 8.46 V and short circuit current of 157 nA) and mechanical performance (compressive modulus of 14.07 MPa). These excellent properties all demonstrate the potential capabilities of the developed piezoelectric nanogenerators in the field of self-powered nanosensors and portable devices.