The rapid growth of intermittent renewable energy (e.g., wind and solar) demands low-cost and large-scale energy storage systems for smooth and reliable power output, where redox-flow batteries (RFBs) could find their niche. In this work, we introduce the first all-soluble all-iron RFB based on iron as the same redox-active element but with different coordination chemistries in alkaline aqueous system. The adoption of the same redox-active element largely alleviates the challenging problem of cross-contamination of metal ions in RFBs that use two redox-active elements. An all-soluble all-iron RFB is constructed by combining an iron–triethanolamine redox pair (i.e., [Fe­(TEOA)­OH]−/[Fe­(TEOA)­(OH)]2–) and an iron–cyanide redox pair (i.e., Fe­(CN)6 3–/Fe­(CN)6 4–), creating 1.34 V of formal cell voltage. Good performance and stability have been demonstrated, after addressing some challenges, including the crossover of the ligand agent. As exemplified by the all-soluble all-iron flow battery, combining redox pairs of the same redox-active element with different coordination chemistries could extend the spectrum of RFBs.

A zinc–iron redox-flow battery is developed that uses low cost redox materials and delivers high cell performance, consequently achieving an unprecedentedly low system capital cost under $100 per kW h.

In this work, a Lattice-Boltzmann-Method (LBM) model for simulating hysteresis in a proton exchange membrane fuel cell (PEMFC) electrode is presented. One of the main challenges hindering study of the cathode catalyst layer (CCL) in PEMFCs is the lack of understanding of two-phase transport and how it affects electrochemical performance. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Using LBM with these representations, the difficult problem of catalyst layer capillary hysteresis can be examined. In two-phase capillary hysteresis, both the equilibrium saturation position as well as its absolute value depends on the wetting history. Based on the models, it is ascertained that at lower capillary numbers, the liquid begins to undergo capillary fingering—only above a capillary pressure of 5 MPa, a regime change into stable displacement is observed. As capillary fingering does not lead to uniform removal of liquid, the prediction is that because high capillary pressures are needed to change to the regime of stable displacement, wicking is not as effective as the primary means of water removal.

Proton-exchange membranes fuel-cells (PEMFC) electrochemical performance insights are predicated on a detailed understanding of species transport in the cathode catalyst layer (CCL). Traditionally, CCL microstructure considerations were approached through approximations with unresolved pore-scale features. Such simplifications cause the loss of predictability for improving the economic feasibility via lower Pt-loading or non-noble metal catalysts. With advances in visualization, microstructure resolved mesoscale models become possible. A judicious combination of lattice Boltzmann (LBM) and finite volume (FVM) is an appropriate strategy for direct numerical simulation (DNS) of the physicochemical fields that remain unresolved due to spatiotemporal limitations.

The ionomer, which is responsible for proton transport, oxygen accessibility to reaction sites, and binding the carbon support particles, plays a central role in dictating the catalyst layer performance. In this work, we study the effect of ionomer distribution owing to the corrosion induced degradation mode in the catalyst layer based on a combined mesoscale modeling and experimental image-based data. It is observed that the coverage of the ionomer over the platinum-carbon interface is heterogeneous at the pore-scale which in turn can critically affect the electrode-scale performance. Further, an investigation of the response of the pristine as well as degraded microstructures that have been exposed to carbon support corrosion has been demonstrated to highlight the kinetic-transport underpinnings on the catalyst layer performance decay.

A Lattice-Boltzmann-Method model for a proton exchange membrane fuel cell (PEMFC) electrode has been presented. One of the main challenges in the development of the cathode catalyst layer (CCL) in PEMFCs is the lack of detailed understanding of species transport and how it affects electrochemical performance. Researchers have typically used high level approximations that oversimplify the microstructure of the CCL—these are known as macrohomogenous models. However, as the field has progressed, these idealizations have begun to show their flaws, especially in areas of improving catalytic performance with lower Pt-loadings and non-noble metal catalysts. Previously, the microstructure details needed to build an accurate mesoscale model have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), creating these representations has become possible. Mesoscale modeling in the CCL has been traditionally approached through either the Lattice-Boltzmann-Method (LBM) or electrochemistry coupled Direct-Numerical-Simulation (DNS). These models have been underutilized in the fuel-cell community due to their complexity and resource intensiveness; however, with advances in parallel computing, this has become not only a possibility, but a necessity for modeling phenomena such as low platinum loadings and interfacial effects. The idea behind this model is to study a particular phenomenon – the effect of current density on saturation. While not the focus of this work, LBM can eventually be coupled with DNS in a synergistic modeling approach. This can shed light on the transport and degradation phenomena in PEMFCs, particularly catalyst layer considerations and carbon support corrosion.

Dedicated to all the wonderful people in my life: Mom, Dad, Chris, and Carmen. Nate Hamilton too for teaching me how to code. iv ACKNOWLEDGEMENTSFirst, I want to graciously acknowledge the people who have shaped me as a researcher. This long and difficult path was not possible without my mother (Cindy Grunewald), father (Jerry Grunewald), and brother (Chris Grunewald), as well as Carmen Chen and Zachary Herde, who have supported me every step of the way at Georgia Tech.I want to thank Dr. Tom Fuller, who I heard wonderful things about from Brian Setzler when I was still in Dr. Yushan Yan's lab at the University of Delaware, for all his guidance throughout these years. I wonder if he still remembers me pestering him if he had made his decision to take me on in Fall 2017 after thermo class. Dr. Fuller gave me a broad license to take this project in any way that I wanted after we developed the code, helping me figure out how to "see the forest from the trees" and broaden my horizons as a researcher. This project would also not have been possible without Dr. Partha Mukherjee and Navneet Goswami, who I collaborated with at Purdue University throughout the length of my PhD and helped shape the researcher I am today. I also wanted to thank Dr. Adam Weber, who graciously allowed me to be at Lawrence Berkeley National Lab over Summer 2021 to adapt my work to a new problem and further improve as a researcher. I also wanted to express gratitude to my wonderful group members for many long nights and inspiring conversations:

The complex dynamics associated with the flooding phenomena in Polymer Electrolyte Fuel Cells (PEFC) need to be appropriately probed in order to facilitate proper water management. In this work, we propose a hybrid Direct Numerical Simulation-Lattice Boltzmann Method (DNS-LBM) framework that enables to investigate such intricate multiphysics coupling. The reaction area passivation and pore blockage which is a consequence of the formation of water as a byproduct from the Oxygen Reduction Reaction (ORR) is implicitly correlated to the geometrical configuration of the catalyst layer microstructure and influences the local electrochemistry leading to mass-transport limitations. In addition, the effect of operating current density on the saturation zones alters the distribution of reaction current within the electrode. This synergistic modeling approach sheds light on the aforementioned mechanisms at the pore-scale and paves the way for detailed understanding of the performance of low Platinum loaded cathode catalyst layers.