Matrix-Assisted Energy Conversion in Nanostructured Piezoelectric Arrays

Abstract

We demonstrate an organic/inorganic hybrid energy-harvesting platform, based on nanostructured piezolelectric arrays embedded in an environmental-responsive polymer matrix, which can self-generate electrical power by scavenging energy from the environment. A proof of principle device is designed, fabricated, and tested using vertically aligned ZnO nanowires and heat as the local energy source. The device layout takes advantage of the collective stretching motion of piezoelectric ZnO NWs, induced by the shapechange of the matrix polymer, to convert the thermal energy into direct current with output power densities of ∼20 nW/cm 2 at a heating temperature of ∼65°C. The responsive nature of polymeric matrices to various stimuli makes this nanostructured piezoelectric architecture a highly versatile approach to scavenging energy from a multitude of environments including fluid-based and chemicalrich systems.KEYWORDS Energy-conversion, piezoelectric, ZnO, Si, hybrid nanogenerator, Seebeck effect E ncouraging progress has been made recently in the development of nanowire (NW)-based piezoelectric nanogenerators. [1][2][3][4][5][6][7][8] In fact, exciting results from various groups working on ZnO, poly(vinylidene fluoride) (PVDF), barium titanate (BaTiO 3 ), and lead zirconate titanate (PZT) have shown device architectures with different powering modes including alternating current (ac) 4-7 and direct current (dc). 9 One key limitation, however, of many piezoelectric-based nanogenerators is the requirement of mechanical energy sources (e.g., mechanical vibration or motion) to generate electrical current. This restricts the use of these nanodevices to a general environment where a direct mechanical energy source is available. To activate the motion of nanopiezoelectric materials through alternate energy sources, such as thermal, photonic, and/or chemical, it will be crucial to investigate new methods of coupling the piezoelectric transducers directly to media that can convert a nonmechanical energy source into piezoelectric strain. This capability will enable materials to be submersed in a variety of environments that have both nontraditional power sources such as mechanical vibrations/motion and pressure gradients as well as traditional power sources such as light, heat, and chemical energy.In this work, we report a self-powered platform that relies on the response of a polymeric film to drive the piezoelectric effect in a nanowire array. To test the concept of polymer facilitated mechanical-to-electrical conversion, we chose to study the well-reported ZnO nanowire system that can be grown by different routes including chemical vapor deposition 10,11 or solution-based techniques 12 and embed the NW array in an environmental-responsive organic polymer. 13 In comparison to other ZnO NW-based nanogenerators, the deformation of the ZnO NWs in our devices are not directly induced by external forces, but rather caused by the shape change in the polymer matrix as it responds to external stimuli. With this hybrid appro...

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