Transition Metal Oxide Nanoparticles Decorated Carbon Nanomaterials as Earth-Abundant Electrocatalysts for Zinc-Air Batteries
Creators: He, Yingjie
Publisher: name: University of Alberta Library
Year: 2022

<p>As awareness of global warming increases and the geopolitically influenced energy supply fluctuates, the global economy is in dire need of a transition from fossil fuels to renewable energy sources. Although renewable energies are sustainable and have favorable environmental impacts, they suffer from their intrinsic intermittency. This creates an imbalance between energy supply and demand on the electric grid. An efficient and cost-effective stationary energy storage technology has the potential of mitigating the energy imbalance while helping to realize the full potential of renewables. Recently zinc-air batteries have become a popular candidate for stationary energy storage owing, in part, to their low cost, high energy density, and safe design. The biggest challenge in commercializing zinc-air batteries, however, is the development of affordable electrocatalysts for the oxygen reduction and oxygen evolution reactions (ORR and OER, respectively) at the air electrode. Traditionally, precious metals such as platinum and ruthenium oxide are used. These materials have obvious drawbacks such as high cost and low earth-abundance. In recent years, transition metal oxide nanomaterials have been explored as alternatives to precious-metal-based catalysts due to their abundance and affordability. Carbon nanomaterials have also garnered attention because of their high surface area, electronic conductivity, and affordability. This dissertation describes the synthesis and characterization of hybrid electrocatalysts that combine transition metal oxide nanoparticles and carbon nanomaterials. These hybrid catalysts outperform common precious metal benchmarks by large margins.<br>
Chapter 1 introduces the current global energy outlook and its associated environmental impact. Subsequent discussion outlines the components and working principles of zinc-air batteries while providing context of the described work in the form of a high-level literature review. Finally, this chapter concludes with detailed descriptions of key characterization techniques used throughout the summarized experiments in Chapters 2 - 4.<br>
Chapter 2 presents an investigation of a hybrid material, namely manganese oxide decorated hollow mesoporous carbon nanospheres (Mn3O4@HMC), as an efficient ORR catalyst for zinc-air batteries. This material was characterized thoroughly using a wide range of techniques and exhibits comparable catalytic performance in both half-cell and full-cell electrochemical testing to commercial benchmark Pt-Ru (30% platinum and 15% ruthenium dioxide on carbon black).<br>
Chapter 3 expands on the foundation of Chapter 2, investigating the decoration of hollow mesoporous carbon (HMC) with other transition metal oxide nanoparticles. This study provided hybrids that excel in catalyzing ORR or OER. More importantly, cobalt oxide nanoparticle decorated HMC (Co3O4@HMC) exhibited excellent bifunctional catalytic activity toward both ORR and OER, outperforming Pt-Ru in both reactions.<br>
Chapter 4 describes a novel annealing method that generates hollow carbon cubes and simultaneously introduces catalytically active metal oxides and alloy nanoparticles using cobalt-based zeolitic imidazolate frameworks (ZIF-67) as a sacrificial template. This method eliminates the need for the dangerous hydrofluoric acid (HF) etching step in the traditional synthesis of hollow carbon nanomaterials (e.g., HMC). The hybrid exhibits promising bifunctional catalytic activity toward both ORR and OER as well as good durability in zinc-air batteries.<br>
Chapter 5 summarizes and concludes the entire dissertation and provides insight into potential future projects.</p>