Low-Temperature Chemical Synthesis of Intermetallic, Carbide, Borocarbide, and Carbonaceous Nanoparticles

Open Access
Author:
Schaefer, Zachary Louis
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 07, 2011
Committee Members:
  • Raymond Edward Schaak, Dissertation Advisor
  • Raymond Edward Schaak, Committee Chair
  • Harry R Allcock, Committee Member
  • Benjamin James Lear, Committee Member
  • Sridhar Komarneni, Committee Member
Keywords:
  • Boron-doped Carbons
  • Carbides
  • Carbonaceous Materials
  • Oxygen Reduction Reaction
  • Nanoparticle Synthesis
  • High Surface Area Materials
Abstract:
Nanoparticles can possess a wide variety of properties that make them capable of being utilized for advanced technological purposes. In many instances, the reliable synthesis of nanoparticles with uniform size, shape, and composition is required to achieve their desired function. Among the methods to produce nanoparticles, low-temperature solution based reactions have emerged as a reliable platform for the synthesis of nanoparticles with tailored size, shape, and composition. In this dissertation, I describe my recent contributions to expanding the diversity of systems and nanostructures capable of being accessed using solution chemical methods. To start off, a conversion chemistry route to make M-Zn intermetallic nanocrystals is described. The generality of this approach is shown by the ability to access PtZn, Ni-Zn, and five distinct Au-Zn intermetallic phases as nanocrystalline materials. The Au-Zn materials represent the most intermetallic phases accessed within a single binary intermetallic system using solution methods to date. Taking the Au-Zn method as a prototype, the possibility for shape preservation of the Au nanoparticle template during the conversion chemistry reaction is demonstrated. Following this, routes to the synthesis of nickel borocarbide and carbide are described. The borocarbide is made using a nano-composite strategy, which utilizes borohydride anion (BH4-) for both reduction of the nickel precursor and as a source for boron. The nickel carbide system is explored in detail and shown to form through a conversion chemistry route, and be capable of having a variety of carbon compositions that can be tuned through carefully modulated isothermal heating. This evidence, along with logical reasoning, is used to help unify existing literature that has claimed separate phases (hcp-Ni and Ni3C) for materials that are likely members of solid solutions of carbon in nickel. Finally, we show how the metastability of carbon in nickel can be used to form high surface area hollow carbon shells at low-temperatures. The C-shells are graphitic in nature, and show enhanced current generation, compared to controls, when used as catalyst supports for Pt during the oxygen reduction reaction (ORR). Evidence is also presented for the unusually low-temperature production of boron-doped hollow carbon shells when using nickel borocarbide as a precursor material. As a result of the electronic modification from the heteroatom doping, these shells could possess a variety of superior properties compared to pure carbon shells.