Nanostructured Materials for Tactile and Catalytic Applications

Abstract

In response to the needs of the modern information-rich society, there is an increasing demand for multifunctional materials with novel properties to advance the development of the new-generation electronics. To synthesize these materials, many biomaterials have been extensively studied and research suggests that their outstanding performance is strongly related to the sophisticated hierarchical structures. Since the development of nanotechnology, numerous nanostructured materials have been reported to exhibit unprecedented performance by mimicking the structures of biological materials. However, there is still a significant gap between experimental research and commercialization of the nanostructured materials, as a result of the typical high-cost fabrication procedures involving lithography or patterning process. Thus, developing new nanostructured materials that can be fabricated with ease can greatly advance their use in practical applications. Inspired by the growth of the biological materials, this dissertation investigates the facile synthesis and explores the use of two types of nanostructured materials, which are three-dimensional hierarchical ZnO nanostructure and self-assembled Au nanoparticle chains.

3-D ZnO nanostructures are synthesized using electrochemical methods by combining 2-D nanosheets with 1-D nanorods. These structures made in high density without any patterning process can be easily assembled over a large area. Upon the application of pressure, the hierarchical structures lead to a highly sensitive and dynamic modulation of the conductive pathways. The tactile sensor made of the high density nanostructured material shows an outstanding sensitivity in the low-pressure regime with a 0.4 Pa limit of detection and a response time of less than 2 ms. The ZnO structures can also detect temperature changes with a non-linear response similar to skin perception in the 298-400 K range. Combining both the pressure and temperature sensitivities, the device is able to differentiate between 20 μl and 40 μl water droplets and also differentiate between 10 μl droplets of room temperature and 323 K. Such performance in a single device which can be prepared by a simple fabrication procedure will bring the tactile sensor closer to skin ability and make this type of devices easily accessible at the same time.

Combining the ferroelectric and semiconducting nature of organolead trihalide perovskite MAPbI3, a light harvesting, self-powered monolith tactile sensor is fabricated. ZnO nanostructure on the MAPbI3 film serve as a pressure-sensitive drain whose interfacing area modulates in response to the applied pressure. The sensor is operational for at least 72 h with just light illumination after consuming 55 µW·h cm-2 energy during the poling process. A linear response is observed till 76 kPa with a sensitivity of 0.57 kPa-1 which can be modulated by the strength of the external electric field.

Additionally, PtRu/Au catalysts for ethanol oxidation is synthesized using self-assembled Au nanoparticle chains linked by Pt4+ and Ru3+ cations. The facile assembly process allows the easy optimization of the relative amounts and relative placement with respect to each other. By inter-mixing the chains at varying stages of assembly, spatial control of distinguishable domains of Pt and Ru on the size of 5-10 nm is achieved. The electrocatalytic activity of the synthesized catalyst is 3.1 times that of commercial Pt/C. The catalyst also shows a higher carbon monoxide-tolerance by negatively shifting the CO oxidation peak for about 0.1 V. Compared to the homogenous mixed catalyst, a 29 % increase of current density is observed for the catalyst with well-defined domains.

The findings of this research therefore provide insights for synthesis of nanostructured materials with unprecedented properties using cost-effective methods instead of complex lithography or patterning process. Such simple fabrication procedures extend our knowledge of preparing and use of similar nanostructured materials in a wide range of applications.