(Invited) Exploring Fuel Cell Catalyst Layers at Multiple Scales

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Integrated Statistical and Nano-Morphological Study of Effective Catalyst Utilization in Vertically Aligned Carbon Nanotube Catalyst Layers for Advanced Fuel Cell Applications

Ionomer is one of the important components in membrane electrode assembly (MEA) of proton exchange membrane fuel cells (PEMFC). It not only acts as an ion exchange membrane for the transfer of protons and water from the anode to the cathode, but more importantly as a binder for gas transport and proton transfer in the catalyst layer. This review focuses on the characteristics and key roles of ionomers in catalyst layers, highlighting the microscopic morphology of ionomers in catalyst inks and catalyst layers. Most importantly, this review plays an important role for the design and functionalization of the lower cost, novel fluorine-free ionomers, which are expected to replace expensive PFSA ionomers.

Comparative analysis between mass and volume of catalysts as a criterion to determine the optimal quantity of Nafion ionomer in catalyst layers

Anion exchange membrane water electrolysis (AEMWE) is a promising technology to produce hydrogen from low-cost, renewable power sources. Recently, the efficiency and durability of AEMWE have improved significantly due to advances in the anion exchange polymers and catalysts. To achieve performances and lifetimes competitive with proton exchange membrane or liquid alkaline electrolyzers, however, improvements in the integration of materials into the membrane electrode assembly (MEA) are needed. In particular, the integration of the oxygen evolution reaction (OER) catalyst, ionomer, and transport layer in the anode catalyst layer has significant impacts on catalyst utilization and voltage losses due to the transport of gases, hydroxide ions, and electrons within the anode. This study investigates the effects of the properties of the OER catalyst and the catalyst layer morphology on performance. Using cross-sectional electron microscopy and in-plane conductivity measurements for four PGM-free catalysts, we determine the catalyst layer thickness, uniformity, and electronic conductivity and further use a transmission line model to relate these properties to the catalyst layer resistance and utilization. We find that increased loading is beneficial for catalysts with high electronic conductivity and uniform catalyst layers, resulting in up to 55% increase in current density at 2 V due to decreased kinetic and catalyst layer resistance losses, while for catalysts with lower conductivity and/or less uniform catalyst layers, there is minimal impact. This work provides important insights into the role of catalyst layer properties beyond intrinsic catalyst activity in AEMWE performance.

Expounding on the results of the author's work with the US Army Research Office, DARPA, the Office of Naval Research, and various defense industry contractors, Governing Lethal Behavior in Autonomous Robots explores how to produce an "artificial conscience" in a new class of robots, humane-oids, which are robots that can potentially perform more et

: Small radial inflow turbines have various applications in industry and are successfully being used as a major component of gas turbines and turbochargers. The performance of the turbine is of great importance for the success of these systems. Although the design of radial inflow turbines has improved in the last few years, the detailed aerodynamic study of these components still needs considerable attention. Better understanding of the flow processes involved in these machines will provide a good basis for the design of improved components and for this purpose a joint research programme has been undertaken by Cranfield, the US Army Research Office and Turbomach (San Diego). The main objective of the study was to investigate the flow processes involved in the radial inflow turbine using experimental methods. The work presented in this report describes the various steps undertaken to perform these studies together with results. The project involved two phases, the first measurements downstream of the rotor and the second measurements between the nozzle guide vanes and rotor inlet. The scope of the study was limited to two man years during which considerable success was achieved in obtaining the desired measurement but more time to further reduce this data and to compare with computational results, which was outside the scope of the present study, would have been advantageous. The studies using laser anemometry undertaken downstream of the turbine rotor indicated a swirling flow with a region of counter-rotating flow in the centre. A cobra probe was used to compare with the laser anemometry results. Both measuring techniques show similar trends of flow velocity and flow angle at various running conditions.... Radial Turbines, Laser Anemometry.

Jagdish Chandra (ed) 1984 Philadelphia: Siam viii + 191 pp price £23.80 ISBN 0 89871 052 9 Chaotic motion is the pseudo-random behaviour of systems governed by deterministic classical equations of motion. Nonlinear dynamics and associated chaotic motion have attracted much research interest in recent years, particularly because the results are applicable to a wide range of problems in science and engineering.

Addition of fillers to polymers has long been used as a strategy to enhance the properties of polymers. In the last two decades, however, a class of materials termed as "polymer nanocomposites" (PNC) has evolved to refer to blends of polymers and inorganic fillers in which the inorganic component has one or more dimensions below 100 nm.1-3 Examples of such materials include mixtures of a variety of homopolymers and multicomponent polymers blended with fillers such as clays, nanotubes, Fullerenes, polyhedral oligomeric silsesquioxanes (POSS), nanoscopic silica particles, and so forth.2-7 Initial interest and research in such materials arose from the significant property enhancements reported for extremely low loadings of nanofillers. These reports fueled intense research into the mechanical, electrical, barrier, and fire retardancy properties of PNCs and have led to some notable commercial technologies utilizing PNCs.1, 8-10 More recent efforts have expanded the above class of studies and materials by examining the properties of nanocomposites involving polymer blends and block copolymers, where the potential to create multifunctional materials possessing novel electrical, magnetic, and optical properties have been reported.11, 12 However, despite the scale of intense research on PNCs, much of the initial promise of PNCs has not yet borne out. In this viewpoint article, I present an (admittedly) personal perspective of some of the issues confronting the field of PNCs, focusing especially on the opportunities by which theory, modeling, and computer simulations from polymer physics may aid in realizing the full potential of PNCs. Many of the common nanofillers used in PNCs are unfortunately characterized by strong van der waals interparticle attractions, which promote their agglomeration.13 Moreover, the effective interactions between nanofillers are also influenced by the polymer-filler interactions, and if the latter are unfavorable, it leads to conditions conducive to the aggregation of the fillers. Aggregation and clustering of the fillers typically leads to a significant reduction in the interfacial contact between the fillers and the polymer and hence a deterioration of the property enhancements that can be attained in PNCs. Consequently, achieving stable, dispersed configurations of nanofillers in the polymer matrix is a prime requirement to realize the full property potential of PNCs. Many experimental strategies have been explo-red to overcome the above challenge.14 These have ranged from using polymer-filler combinations, which are known to exhibit favorable affinities to functionalizing the fillers by self-assembling surfactant and grafting polymers to promote favorable polymer-filler interactions (and provide a steric barrier against agglomeration). Also, successful strategies using external fields to promote nonequilibrium dispersion of the nanofiller have been demonstrated.15 From a theoretical perspective, the outstanding question confronting the design of such strategies is "For specified combination of matrix polymer(s), filler(s), the functionalizing moieties and/or external fields, can we predict the equilibrium and nonequilibrium structural characteristics of the PNC dispersion?" Anisotropy of fillers: Most of the PNCs explored for applications involve filler particles such as clays, carbon nanotubes, nanofibers, and so forth, which exhibit considerable shape anisotropy. Indeed, such fillers prove most suitable for exploiting significant polymer-filler interfacial contact at even extremely low loadings of the filler. In contrast, very few of the aforementioned theories and simulations deal with the phase behavior and structure of mixtures of anisotropic fillers dispersed in single and multicomponent polymers.27-29 The rich literature of colloidal physics suggests that the equilibrium characteristics of anisotropic colloids can be expected to be significantly different and richer compared with their isotropic counterparts.30 Moreover, situations combining anisotropic fillers with multicomponent polymers such as block copolymers can be expected to reveal a rich interplay between polymer self-assembly and colloidal phase behavior. It will be of significant interest to PNC research to translate some of the theoretical advances achieved in the context of spherical fillers to the corresponding situations involving anisotropic fillers. Role of Functionalization: As mentioned earlier, functionalization of the fillers is a common strategy to overcome the issue of agglomeration of fillers. However, in much of the existing theories, the role of functionalization is treated either empirically as a modified polymer-filler interaction18, 23 or in more detailed formalism as a modification of the effective polymer-mediated potentials between the fillers. The first approach can be deemed reasonable for small oligomeric or surfactant-like functionalizers, but suffers from the drawback that it leaves open the question of the relationship between the polymer-filler interaction and the physicochemical properties of the functionalizing group. The second approach has typically been effected for the situation of grafted polymer functionalizers.31 It is, however, a pairwise interaction approach that works only for the homogeneous phase of the polymer matrix and in addition neglects multibody effects, which may become important when either long grafting polymers or higher concentrations of fillers are used. Overall, it would be desirable to develop a suite of simulations and/or modeling tools that, similar to the nongrafted case, can obviate such assumptions while still being able to predict the structure of the PNC dispersion. Structure under nonequilibrium and external field conditions: Despite the best experimental strategies, nonequilibrium effects resulting from filler aggregation and/or external fields are bound to remain important for many applications of PNCs, especially for situations involving anisotropic fillers. Some unresolved questions include: "How does the structure of a PNC dispersion evolve upon dispersing the fillers in the polymer matrix?," "Can quantities such as the fractal dimension and cluster size distributions be predicted for specified polymer-filler combinations?," "How does externally applied shear, electric, and magnetic fields (and combinations thereof) impact upon the nonequilibrium state of the dispersion?" Although computer simulations may shed light on some of the relevant issues, the time and length scales, which can be probed by such means may not necessarily overlap with experimental regimes, and there is a need for development of appropriate theoretical models to address pertinent issues. There have been some notable theoretical advances in this regard in the context of colloidal science,32, 33 and a preliminary assessment of their applicability to the field of PNCs would be extremely beneficial. However, issues unique to PNCs, such as the significant anisotropy of the fillers, potentially long-ranged interparticle interactions (mediated by the polymers), the dynamical and rheological response of the polymer matrix, are expected to prove important and provide fertile and challenging areas for theoretical research. Detailed structural characteristics: Many experimental studies of the mechanical, electrical, and rheological behavior of PNCs have suggested an intimate connection between enhanced macroscopic properties and the percolation behavior of the fillers.10, 34-36 Although such features can be directly extracted in computer simulations, existing theoretical frameworks mostly concern with the phase behavior and/or structural features at a pair correlation level. It may be of interest to the PNC experimental community to develop a theoretical framework, which can predict the the influence of different interactions, functionalization, and external fields upon more detailed structural characteristics such as the percolation characteristics37, 38 fractal and cluster dimensions of the fillers in the polymer matrix. Connection to atomistic details: Much of the above discussion focused on some open questions in the context of structure of PNCs as examined from a "coarse-grained" polymer physics perspective. Although such efforts are valuable for providing design guidelines, deducing mechanistic underpinnings and suggesting new experimental strategies, questions involving the detailed chemistry of the filler, polymer and functional groups cannot typically be answered in such frameworks. This situation is compounded by the fact that much of the coarse-grained modeling of PNCs use potentials and interaction parameters, which cannot also be directly determined from experimental measurements. The latter contrasts with the analogous situation in multicomponent polymer melts and solutions where experimental solubility measurements provide direct information on the parameters used in the corresponding coarse-grained theories.39 Addressing this shortcoming in the context of PNCs requires the development of efficient computer simulation tools and methodologies, which can render the connection between the chemistry of the components and the coarse-grained parameters more quantitative. The research field of "coarse-graining methodologies" is undergoing intense development in the context of simple and polymeric fluids.40-42 Although some notable "multiscale" efforts have also occurred in the context of PNCs,43, 44 much work remains to be done in surmounting the time, length scale challenges accompanying the interactions, structure, and properties of PNCs. Detailed structural information: Much of the aforementioned macroscopic theories were developed for model structural representations such as random or completely aligned dispersions while ignoring PNC specific features such as aggregation and/or complex structural arrangement of the fillers. Consequently, it is not surprising that such ideal models cannot quantitatively predict the properties of PNCs. One potential area for future research is the development of macroscopic models capable of accommodating detailed structural information, such as experimentally obtainable pair correlation functions of the fillers or cluster sizes and fractal dimension of aggregates, while rendering quantitative predictions regarding the macroscopic properties of PNCs. This area has recently seen some notable advances, especially arising from numerical continuum mechanical approaches.47-49 It may be envisioned that the results of such efforts can be used to guide the refinement of classical models to accommodate the PNC specific features. Interfacial effects: An important feature that distinguishes PNCs from traditional composites is the presence of significant amounts of polymer-filler interfaces and its influence upon the macroscopic properties. To highlight the resulting issues, I point out the status with respect to the "simpler" situation of polymer films supported on a solid substrate. In such contexts, experiments have clearly demonstrated that the polymer-surface interactions can lead to properties for the polymer layer, which are in general markedly different from that of the bulk polymeric material.50 Moreover, for properties such as glass transition temperatures,51 aging dynamics,52, 53 and elastic moduli,54 the interfacial effects have been shown to persist to extremely long length scales relative to the physical dimensions of the polymer. In the context of properties that exhibit only a short ranged interfacial effects (such as solubility of penetrants and mechanical properties), the aforementioned approaches may suffice to accommodate the influence of polymer-filler interfaces upon macroscopic properties. However, to endow a predictive value to theories, quantitative connections between the physicochemical polymer-filler interactions and the properties of the interfacial layer (or the parameters in the boundary conditions) in such models needs to be established. Although computer simulations may aid in this effort, in many cases, new formalisms may be necessary to discern quantities such as "local" mechanical properties,55 "local" conductivities, "local" penetrant diffusivities, and so forth, in such efforts. Once the connections between polymer-filler interactions and the interfacial properties are firmly established, "homogenization theories" similar to that used for the macroscopic properties of composites and dispersed media may be pursued. However, such approaches still need to be augmented to account for the possibility of complex structural arrangement of the fillers (an issue discussed earlier) and the overlap of interfacial layers which may consequently arise. As discussed earlier, some interfacial properties (such as the glass transition temperatures) are known to display long ranged variations influenced by the surface of the fillers, and in such cases, boundary condition and/or three-phase model approaches are likely to prove inadequate for capturing the influence of polymer-filler interfaces upon the macroscopic properties of the system. Refining the existing models to account for such properties represents an extremely challenging task, because in many cases there is a lack of understanding of the physics underlying such long ranged variations in polymer thin films. Moving to PNCs brings even more complications, such as the possibility for overlap of interfacial layers arising from different particles (such overlaps become very likely for long-ranged effects), leading to significant multibody interaction effects. Overall, this is an area for which the directions of theoretical modeling are far less clear (to me), suggesting that radically new ideas may be necessary to make progress in understanding and predicting the properties of polymer thin films and PNCs. The above represents an opinionated selection of some of the open questions confronting theoretical modeling of polymer nanocomposite systems. While active research is in progress in a number of the above-mentioned areas, successful fruition in many of the issues requires a confluence of ideas from different fields, viz., colloid and polymer physics, statistical and continuum mechanics, modeling and simulation approaches, and most importantly, experiments and theories. While technology and experiments are likely to provide more focus to the issues and theoretical efforts, progress in the above delineated issues is expected to have significant fundamental implications for many related areas of polymer and colloidal science, and may also potentially lead to uses and applications of PNCs above and beyond what has been realized or even dreamed about. This research program on polymer nanocomposites has been graciously supported by research grants from the National Science Foundation, American Chemical Society, Air Force Research Laboratories, Robert A. Welch Foundation, and the US Army Research Office under grant W911NF-07-1-0268. The author thanks Dr. Victor Pryamitsyn for useful comments which helped to shape the ideas expressed in this viewpoint. The author also acknowledges Profs. Glenn Fredrickson, Kenneth Schweizer, John Torkelson, Peter Green, Donald Paul, Jack Douglas, Sanat Kumar, Richard Vaia, and Ramanan Krishnamoorti for many discussions over the years while patiently educating him on the issues in polymer nanocomposites.

: US Army Research Office has funded this 2-year basic research effort by ICx-Agentase to study new techniques of modifying native enzymes with polymers via atom transfer radical polymerization to increase their solubility and utility in organic solvents and to increase their stability in body. Protein-initiated ATRP would enable us to overcome many problems in conventional technology that modifies proteins with polyethylene glycol or pegylation. These problems include lack of control on number of polymer chains attached per protein, low yield, tedious purifications, and less-than-optimal stabilization. The first goal of this study is to develop new technique/s to modify enzymes with hydrophobic polymers and dissolve high concentrations of modified enzymes in organic solvent and apply them in self decontaminating paints and coatings. The second goal of the study was to study the potential of using of ATRP modified proteins for therapeutic applications in vivo. Chymotrypsin and BChE conjugates synthesized by ATRP were demonstrated and were highly active and much more stable in mouse serum as compared to conventionally pegylated enzymes.

Annals of the New York Academy of SciencesVolume 410, Issue 1 p. 323-337 THERMAL AND SHOT NOISE EFFECTS ON NONLINEAR OSCILLATORS* E. Ben-Jacob, E. Ben-Jacob Department of Physics and Astronomy Tel Aviv University Tel Aviv, Israel Institute of Theoretical Physics, University of California, Santa Barbara, California 93106.Search for more papers by this authorD. J. Bergman, D. J. Bergman Department of Physics Ohio State University Columbus, Ohio 43210 Permanent address: Department of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.Search for more papers by this authorB. J. Matkowsky, B. J. Matkowsky Department of Engineering Sciences and Applied Mathematics Technological Institute Northwestern University Evanston, Illinois 60201Search for more papers by this authorZ. Schuss, Z. Schuss Department of Engineering Sciences and Applied Mathematics Technological Institute Northwestern University Evanston, Illinois 60201 Permanent address: Department of Mathematics, Tel Aviv University, Tel Aviv, Israel.Search for more papers by this author E. Ben-Jacob, E. Ben-Jacob Department of Physics and Astronomy Tel Aviv University Tel Aviv, Israel Institute of Theoretical Physics, University of California, Santa Barbara, California 93106.Search for more papers by this authorD. J. Bergman, D. J. Bergman Department of Physics Ohio State University Columbus, Ohio 43210 Permanent address: Department of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.Search for more papers by this authorB. J. Matkowsky, B. J. Matkowsky Department of Engineering Sciences and Applied Mathematics Technological Institute Northwestern University Evanston, Illinois 60201Search for more papers by this authorZ. Schuss, Z. Schuss Department of Engineering Sciences and Applied Mathematics Technological Institute Northwestern University Evanston, Illinois 60201 Permanent address: Department of Mathematics, Tel Aviv University, Tel Aviv, Israel.Search for more papers by this author First published: July 1983 https://doi.org/10.1111/j.1749-6632.1983.tb23331.xCitations: 4 * This research was supported, in part, by grants from the US Department of Energy, no. DE-AC02-78ERO-4650, from the US Army Research Office, no. DAAG29-79-C-0183, from the US Air Force Office for Scientific Research, no. 78–3602C, from the Israel Academy of Sciences, no. 707, and from the National Council for Research and Development, Kernfor-schungszentrum, Karlsruhe, West Germany. One of us (BJM) gratefully acknowledges the support of a John Simon Guggenheim Memorial Foundation Fellowship. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume410, Issue1Fifth International Conference on Collective PhenomenaJuly 1983Pages 323-337 RelatedInformation

Lattice Boltzmann Pore-Scale Investigation of Coupled Physical-electrochemical Processes in C/Pt and Non-Precious Metal Cathode Catalyst Layers in Proton Exchange Membrane Fuel Cells

The perfluorosulfonic acid (PFSA) ionomer commonly used in Polymer Electrolyte Membrane Fuel Cells (PEM-FC) consists of a hydrophobic tetrafluoroethylene backbone with side chains terminated with sulfonate groups responsible for proton conduction. Optimizing the spatial distribution of ionomer in the catalyst layer maximizes the catalyst that is accessible to protons and O2, reducing the Pt loading. Thus, the methods of quantifying the distributions of ionomer relative to catalyst are important. PFSA is prone to radiation damage [1], losing fluorine which makes it challenging to analyze quantitatively with electron [2] and x-ray spectro-microscopies [3]. Scanning Transmission X-ray Microscopy (STXM) is known to cause less damage in soft materials than analytical Transmission Electron Microscopy (TEM), with either core level Electron Energy Loss (EELS) [4] or Energy Dispersive X-ray Spectroscopy (EDS). We have applied Scanning TEM – EDS (STEM-EDS) and STXM at room temperature to the same microtomed sample of a PEM-FC catalyst layer. STEM-EDS was performed using an FEI Tecnai Osiris equipped with CHEM-STEM 4 area detectors. STXM was performed using soft X-ray STXMs at the Canadian Light Source (Saskatoon) and the Advanced Light Source (Berkeley). The extent of ionomer damage (F-loss) as a function of absorbed radiation dose in the cathode due to each imaging technique was measured from F Ka maps in STEM-EDS, and by F1s stack maps (OD694 eV - OD684 eV) in STXM. Figure 1 plots the extent of fluorine signal and thus component loss, normalized to the initial amount, for a range of electron and X-ray exposures. Both the electron and X-ray beams damage the ionomer at a similar rate. However, decent quality EDS maps at room temperature (Figure 1C) with sufficient counts for statistical analysis need ~30000 e-/nm2. At that exposure, approximately 70-80% of the original fluorine signal in the ionomer material is lost. On the other hand, high quality ionomer maps using STXM require less than 10 photons/nm2 (Figure 1A), which causes negligible fluorine loss. The ‘multi’ mode of TEM-EDS acquisition does provide significantly less damage at lower exposures (Figure 1B) but by the time adequate image quality is achieved (Figure 1C), the extent of fluorine loss is unacceptably high. Whether the ionomer damage is attributed to only fluorine loss (EDS), or ionomer component loss (STXM), or significant change of ionomer chemistry is still debatable. However, this study indicates that after applying “common” imaging practices for STXM and EDS, the remaining cathode areas are significantly different. STXM performed on BL 10ID1 at CLS and on BL 5.3.2.2 at ALS. Research supported by NSERC and the Catalyst Research for Polymer Electrolyte Fuel Cells (CaRPE-FC) network. S. Yakovlev, et.al., Membranes. 3(2013) 424–439D.A. Cullen, et al., J. Electrochem. Soc. 161 (2014) F1111–F1117D. Susac, et.al. STXM ECS Trans. 41 (2011) 629–635J. Wang, et.al., J. Phys. Chem. B. 113 (2009) 1869–76. Figure 1

Effect of compression on pore size distribution and porosity of PEM fuel cell catalyst layers

Optimizing the water management in proton exchange membrane fuel cells (PEMFCs) is paramount to improving their performance at high current densities. Numerical models describing the physical processes in the PEMFC are an important tool to analyze and understand experimental results and optimize the performance with respect to material properties and operating conditions. Macro-scale models of PEMFCs describing two-phase flow have previously been developed (1, 2). These models rely on effective transport properties and morphological information of the porous layers, such as pore size distribution (PSD), to accurately describe the physical processes. These properties are often estimated using empirical correlations (1). Microstructural modeling provides a feasible alternative to estimate the required transport properties based on the morphology of the porous layers. Microstructural models describing gas transport and liquid water intrusion have previously been developed for gas diffusion layers (GDLs) (3) and micro-porous layers (MPLs) (4). For catalyst layers (CLs), microstructural models describing the transport and electrochemical reactions under dry conditions are available in literature (5, 6). However, very few studies (7, 8) have accounted for liquid water intrusion in the CLs and the corresponding effect on the transport properties and electrochemical performance. The aim of this work is to develop numerical models to simulate liquid water intrusion in the fuel cell CLs and study the corresponding effect on the transport properties and performance. A focused ion beam-scanning electron microscopy (FIBSEM) CL reconstruction is used to study gas and charge transport and liquid water intrusion in the CL. Liquid water intrusion in the CL is simulated using a full morphology based model. In-situ μ-CT data was used to validate the liquid water intrusion model. The validated model will be used to simulate liquid water intrusion in CLs with different modes of injection such as nucleation (8), PSD based (7) and boundary based (9). The obtained saturation distributions in the CLs would be used as meshes for continuum simulations to study the changes in the effective diffusivity and electrochemical performance of the CLs. For the electrochemical simulations, charge transport is simulated in an ionomer film and oxygen transport is simulated in the ionomer, pores and liquid water. Figure 1a shows a schematic of a single pore with ionomer film and the reaction boundary. Since FIBSEM does not provide any information about the ionomer, carbon or platinum, it is assumed that the ionomer forms a thin film at pore-solid interface. This film is digitally reconstructed based on the composition of the CL. The reaction is simulated at the ionomer-solid interface assuming that the solid interface corresponds to platinum particles. The numerical framework for the microscale simulations has been developed in the open-source package OpenFCST (10). The current results show that the different modes of water injection result in different threshold saturations, i.e., the saturation at which percolating pore volume for gas transport is lost. The effective diffusivity of oxygen reduces with an increase in saturation. Electrochemical simulations on partially saturated CLs are underway.