Studies of Electronically Perturbed Polyoxometalate Catalysts Open Access

Abstract

           Polyoxometalates (POMs) are polyanionic metal-oxo species that are closely related to metal oxides and capable of a large number of catalytic reactions. However, due to their discrete molecular nature, POMs are suitable for everything from unitary atomic modification to larger scale bulk polymerization. Utilizing this unique aspect of POMs, we devise synthetic strategies that modulate existing POM catalysts through atomic substitution, counterion permutations, and ligand framework adaptation. This is all done in the context of the prominent catalytic reaction of water oxidation, ultimately achieving a number of electronically perturbed POM water oxidation catalysts (WOCs).

           The synthesis of these POM WOCs allows us to directly study the effect of electronic perturbation on the reaction mechanism of these catalysts and how that relates to their observed catalytic performance. This degree of atomic control is not generally available to analogous bulk and crystalline heterogeneous metal oxides and provides new insights for both the oxygen evolution reaction (OER) catalysis and for metal-oxo based reactions. Moreover, the molecular nature of these POM WOCs gives additional handles with which we can use for characterization.

           Chapter 1 gives the broader scope for which this work is relevant. Chapter 2 and 3 proposes the rational design, synthesis, and characterization of an atomically modified mixed-metal POM catalyst. Chapter 4 examines an unprecedented observed trend in counter-cation identity and catalytic reactivity. Chapter 5 investigates the role of ligands in copper-oxo cluster WOCs and the accompanying stabilization that results. Chapter 6 looks at common characterization techniques for probing the catalytic performance of molecular WOCs and reevaluates their broad adaptation in the context of electrochemistry to couple thermodynamics and kinetics and give additional mechanistic insights.

Table of Contents

Table of Contents

Chapter 1: The Basics

Overview

Water oxidation reaction

References

Chapter 2: Electronic Perturbation of Transition-Metal Catalytic Water Oxidation Sites of Isostructural and Isocharge Polyoxometalates

Introduction

Results and Discussion

Experimental

Conclusion

References

Chapter 3: Electronic Spectroscopy of the Effect of Elemental Substitution in Isostructural Polyoxometalate Water Oxidation Catalysts

Introduction

Results and Discussion

Experimental

Conclusion

References

Chapter 4: Effects of Counter Cations on Polyoxometalates Redox Properties and Oxygen Evolution Catalysis Performance

Introduction

Results and Discussion

Experimental

Conclusion

References

Chapter 5: Stabilization of a Copper-Oxo Unit in Base Utilizing Polyoxoniobates

Introduction

Results and Discussion

Experimental

Conclusion

References

Chapter 6: Tafel Slope Analyses for Homogeneous Catalytic Reactions

Introduction

Results and Discussion

Experimental

Conclusion

References

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Chemistry, Inorganic Chemistry, General Chemical Oceanography
Keyword	water oxidation electronic perturbation catalyst polyoxotungstate polyoxoniobate Tafel XAS acid stable cobalt base stable catalysis counterion electronic spectroscopy EXAFS polyoxometalate XANES transition-metal mixed-metal
Committee Chair / Thesis Advisor	Craig L. Hill, Emory University
Committee Members	Djamaladdin G. Musaev, Emory University Cora MacBeth, Emory University Tianquan Lian, Emory University

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