Nanomaterials for thermoelectric energy conversion

Michael P Tate, Purdue University

Abstract

Increasing worldwide energy demand over the next 25 years will drive development of high-efficiency, cost-effective energy conversion devices such as nanostructured thermoelectric power generators. Thermoelectric power generators recover energy from waste heat in the form of electricity, but modern thermoelectric device efficiencies are below the level at which wide spread use becomes practical. Development of new nanomaterials, through advances in nanoscale science and engineering, will offer new routes to reduce the costs and increase the efficiencies of nanostructured thermoelectric devices. The key achievement necessary to enable the possibility of nanostructured thermoelectric devices is development of large parallel arrays of nanowires with diameters less than 4 nm. Nanowire arrays enhance the efficiency of the devices, and thereby reduce overall cost, through quantum confinement of the electron transport within the materials. One robust method to synthesize large parallel arrays of nanowires is a hard-templating approach of nanoporous films followed by electrochemical deposition within the nanopores. Evaporation-induced self-assembly (EISA) of surfactant molecules with metal oxide oligomers is particularly robust at producing highly periodic, monodisperse nanopores of appropriate length scale. In addition, EISA is a room temperature, liquid phase, scalable process, which has a cost advantage over competing vapor phase processes. However, understanding of key processing variables that control the formation of film topology remains elusive, in part due to the lack of characterization methods and analytical tools. In this dissertation, I describe my development of grazing incidence small angle x-ray scattering tools to quantitatively characterize highly ordered nanostructured films, and show how I have used these tools to understand and control the nanostructure and topology of nanoporous films. In particular, a simple and reproducible method to self-assemble highly ordered and oriented double-gyroid symmetry nanoporous films has been developed, in which the films have facile mass transport of solution phase ions from the surface, through the film, and to the underlying substrate. This breakthrough has enabled the use these nanoporous films as templates for the electrochemical deposition metal and semiconductor nanowire networks with 4 nm diameters. Finally, I describe a future research framework for measurement of thermoelectric properties from the embedded nanowire networks.

Degree

Ph.D.

Advisors

Hillhouse, Purdue University.

Subject Area

Chemical engineering

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