Piezoelectric Nanogenerator developed by Dr. Yong Shi
Piezoelectric nanomaterials: The piezoelectric properties of several nanowires, nanofibers, and nanorods made from zinc oxide, lead zirconate titanate (PZT), cadmium sulfide, barium titanate, and gallium nitride have been successfully demonstrated. These one-dimensional piezoelectric nanostructures convert mechanical energy into electrical energy. These nanogenerators have been successfully demonstrated for potential applications in converting low-frequency vibration and biomechanical energy into electrical energy.
But for practical applications the piezoelectric voltage constant of the piezoelectric nanomaterials and output voltage and power of the nanogenerators still needs further improving. It is also difficult to grow single crystal nanowires longer than 50 μm with diameters less than 100 nm. The nanogenerator fabrication method and the output voltage of the nanogenerator could be significantly restricted by the short length of nanowires.
Lead zirconate titanate (PZT): PZT is a widely used piezoelectric ceramic material with high piezoelectric voltage and dielectric constants, which are ideal properties of active materials for mechanical to electrical energy conversion. For a given volume under the same energy input, PZT can generate much higher voltage and power outputs than other semiconductor types of piezoelectric materials.
As a ceramic material, bulk and thin film PZT structures are extremely fragile, especially when subjected to alternating loads. Also these thin film and microfiber structures are typically sensitive to highfrequency vibration. However, unlike bulk, thin films or microfibers, PZT nanofibers prepared by an electrospinning process exhibit an extremely high piezoelectric voltage constant (g33, 0.079 Vm/N), high bending flexibility, and high mechanical strength.
Piezoelectric Nanogenerator developed by Dr. Yong Shi and colleagues
In order to overcome some of the inherent drawbacks of the existing nanogenerators, Dr. Yong Shi, a professor in the Mechanical Engineering Department at Stevens Institute of Technology, has developed a highly efficient nanogenerator based on laterally aligned lead zirconate titanate (PZT) nanofibers on interdigitated electrodes
The nanogenerator device fabrication began by electrospinning18 PZT nanofibers and depositing them on the preprepared interdigitated electrodes of platinum fine wire (diameter of 50 μm) arrays, which were assembled on a silicon substrate. The diameters of PZT nanofibers were controlled to be around 60 nm by varying the concentration of poly vinyl pyrrolidone (PVP) in the modified sol-gel solution. The PZT nanofibers obtained were continuous, while the distance between two adjacent electrodes was 500 μm as designed. A pure perovskite phase was obtained by annealing at 650 °C for about 25 min. Subsequently, a soft and polymer (polydimethylsiloxane, PDMS) was applied on top of the PZT nanofibers. The interdigitated electrodes of fine platinum wires were connected by extraction electrodes to transport harvested electrons to an external circuit. Finally, the PZT nanofibers were polled by applying an electric field of 4 V/ μm across the electrodes at a temperature of above 140 °C for about 24 h. The nanogenerator can be released from the silicon substrate or prepared on flexible substrates, depending on the requirements of the applications for energy harvesting.
Nanogenerator
According to the researchers the peak output voltage from this nanogenerator was 1.63 V, and the output power was 0.03 μW with a load resistance of 6MΩ. The piezoelectric voltage constant and dielectric constant of PZT nanofibers were much higher than those of the semiconductor type of piezoelectric nanowires and nanofibers, making this material ideal for nanogenerator or nanobattery applications. The flexible PZT nanofibers were embedded in soft polydimethylsiloxane (PDMS) polymer matrix, which helped prevent the PZT nanofibers from being damaged, thereby extending the life cycle of the nanogenerator.
The researchers claim because the fabrication and assembly process involved in producing the nanogenerator is very simple, it can be easily mass produced.
According to Dr. Shi and his colleagues utilizing PZT nanofibers in energy harvesting technology could provide a new way to make a portable, flexible, highly efficient device with a low-frequency vibration nature, since the nanofibers could be woven into fabrics and made into composites.
The other members of the research team are Xi Chen, Shiyou Xu and Nan Yao.
Source: http://www.princeton.edu/~iac/nan/pdf/Nano%20Letter1%202010.pdf
July 12, 2010