| dc.description.abstract | Electrochemical systems offer a pathway toward directly harnessing sustainable electricity to manage intermittency in renewable power production, decarbonize transportation, and unlock new routes for chemical and material production. However, to compete with their thermochemical counterparts, emerging electrochemical processes of interest must achieve lower system costs, higher efficiencies, and longer operating lifetimes. Redox-mediated electrochemical systems are an emerging technology concept that could aid in addressing these challenges. These devices utilize a chemical looping approach, where a soluble mediator species is circulated between an electrochemical reactor – where it is activated – and a chemical reactor – where the activated mediator drives an “off-electrode” chemical redox reaction. This decoupling of the desired chemical transformation of interest from the electrochemical reactor simultaneously alters the underlying design landscape, offering new routes toward cost-effective reactor architectures and conversions. Mediated processes have been demonstrated to improve the energy density of redox flow batteries, catalyze impractical or inefficient electrochemical transformations, increase selectivity and efficiency of separations and recycling, and facilitate spatial and temporal flexibility in chemical manufacturing. However, the complex interplay of the reactors and multiple active species obfuscate the underlying behavior of these systems, hindering efforts to understand, improve, and scale. In this dissertation, I develop a continuum model framework capable of capturing and rationalizing the thermodynamics, reaction kinetics, and transport phenomena that govern the performance dynamics of redox-mediated systems for energy storage and conversion. Leveraging (electro)chemical engineering principles and drawing upon mixed potential theory (originally developed to describe metallic corrosion), the framework qualitatively tracks the results of multiple experimental redox-mediated systems. Such findings suggest the framework is capable of providing insight into new avenues to probe questions related to system design and operation. I begin by relating physical and operating parameters to system-level performance trends in redoxmediated flow batteries, including revealing performance regimes and a dimensionless “collapsed relationship” for solid utilization and tradeoffs in system energy and power. Guided by the assumptions and consequences of the underlying theory, I then pursue a suite of modeling and empirical analyses to uncover the implications of different system designs and operational protocol. Specifically, I investigate how “delocalized” charge transfer in conductive composites, cycling protocol, active material degradation, non-ideal thermodynamics, and intraparticle transport are anticipated to alter the underlying dynamics and system performance of redoxmediated flow batteries. Toward the end of this work, I shift to analyzing emerging redox-mediated systems relevant to industrial chemical transformation, exploring case studies in continuously mediated solid transformations and mediated gas evolving reactions. Finally, I depart from the theme of this dissertation to briefly explore how dynamic thixotropy structure parameter expressions can dynamically regularize viscoplasticity in rheological models, which could aid in advancing non-Newtonian fluid mechanics simulations of emerging devices employing flowable suspension electrodes. Ultimately, the goal of this dissertation is to aid in the development of theory, analysis tools, and design principles that guide the study, development, and enhancement of emerging redox-mediated systems for sustainable energy conversion and storage. | |
