Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. Thomas John Balk

Abstract

Nanoporous (np) materials with pore size below 100 nano-meters exist naturally in biological and mineral structures, and synthetic np materials have been used industrially for centuries. Np materials have attracted significant research interest in recent decades, as the development of new characterization techniques and nanotechnology allow the observation and design of np materials at a new level. This study focuses on two np materials: nanoporous silicon (np-Si) and nanoporous palladium (np-Pd).

Silicon (Si), because of its high capacity to store lithium (Li), is increasingly becoming an attractive candidate as anode material for Li ion batteries (LIB). One significant problem with using Si as an anode is the large strain that accompanies charge-discharge cycling, due to swelling of the Si during Li insertion and deinsertion. Np-Si offers a large amount of free volume for Li absorption, which could allow the anode material to swell without cracking. A new method to fabricate thin films of high-purity (100% Si content) np-Si, which is promising as an anode material for LIB, is demonstrated and discussed in this study. Microstructural characterization, chemical analysis, battery performance testing and mechanical behavior of thin film np-Si are discussed here.

Palladium (Pd) is considered an ideal and reliable hydrogen sensor and storage material, due to its fast response and selectivity for hydrogen gas. This research not only demonstrates a method to fabricate np-Pd thin films, but also proposes a method to fabricate bulk np-Pd. The uniformly crack-free and sponge-like np-Pd thin film provides high sensitivity to low concentrations of H2, showing promise as a hydrogen sensor material. Stress changes during hydrogenation/dehydrogenation were measured using wafer curvature. For bulk np-Pd, ultra-fine pore sizes were achieved by electrochemically dealloying bulk PdNi alloy. Mechanical behavior of bulk np-Pd was studied using in-situ transmission electron microscopy (TEM). Scanning electron microscopy (SEM) and x-ray diffraction were also used to characterize the structure and morphology of np-Pd.

This doctoral research has involved the optimization of fabrication conditions and investigations of microstructural evolution during processing, yielding an improved understanding of the properties, mechanical behavior and potential applications of np-Si and np-Pd.

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