Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Chemistry

Major

Chemistry

First Advisor

Wenyu Huang

Abstract

Electrocatalysis plays a critical role in the clean energy conversions nowadays, such as fuel cells and batteries. With the increasing population and energy demands, people are aiming to build a global-scale sustainable energy system in the future, which could convert the abundant N2, O2, water into more useful chemicals and fuels via electrocatalysis and electricity from renewable energies (e.g., wind, solar energy). Therefore, there is an urgent need to design electrocatalysts with higher activity, better stability, and higher selectivity. Two strategies are commonly applied to enhance the activity: 1) increase the number of active sites and 2) increase the intrinsic activity of each active site. By using support and alloying in our research, we could achieve both strategies simultaneously.

In this dissertation, I present several examples of confined intermetallic nanoparticles and MOF-derived nanomaterials for enhanced electrocatalysis. In chapter 2, I synthesized sub-4 nm monodispersed PtZn intermetallic nanoparticles supported on carbon nanotubes with the protection of mesoporous silica shell via high temperature annealing. Both specific activity and mass activity towards methanol oxidation reaction of smaller PtZn nanoparticles are greatly enhanced, revealing that the smaller particles not only increase the number of active sites but also increase the intrinsic activity of each site. Moreover, both DFT calculation and experimental results indicating PtZn systems go through a “non-CO pathway”, due to the stabilization of the *OH species by Zn atoms. Chapter 3 shows a facial synthesis of intermetallic nanoparticles as electrocatalysts via one-pot pyrolysis of ZIF-8 encapsulated metal nanoparticles. ZIF-8 works as both carbon source, zinc precursors, encapsulation shell in the formation of zinc-containing intermetallic nanoparticles supported by nitrogen doped carbon. This method allows the fine tuning of particle size and composition, and more importantly, provides high thermal stabilities up to 1000 ˚C. In chapter 4, I showed the enhanced hydrogen evolution activity of ordered Pt3Ti intermetallic nanoparticles supported by Ti3C2 Mxene sheet. We further demonstrated the enhanced activity is due to the strong synergistic effect between Pt3Ti and Mxene support. Chapter 5 shows the morphology inherence from hollow ZIFs to hollow carbons with superior activities of oxygen reduction reaction. The designed hollow carbons are not only having better mass transfer but also able to introduce the heteroatoms such as Fe onto the inner wall, which could promote the activity of ORR.

Copyright Owner

Zhiyuan Qi

Language

en

File Format

application/pdf

File Size

157 pages

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