Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application

X-ray Photoelectron Spectroscopy Analysis of Nafion-Containing Samples: Pitfalls, Protocols, and Perceptions of Physicochemical Properties

X-ray photoelectron spectroscopy (XPS) is one of the most common techniques used to analyze the surface composition of catalysts and support materials used in polymer electrolyte membrane (PEM) fuel cells and electrolyzers, providing important insights for further improvement of their properties. Characterization of catalyst layers (CLs) is more challenging, which can be at least partially attributed to the instability of ionomer materials such as Nafion during measurements. This work explores the stability of Nafion during XPS measurements, illuminating and addressing Nafion degradation concerns. The extent of Nafion damage as a function of XPS instrumentation, measurement conditions, and sample properties was evaluated across multiple instruments. Results revealed that significant Nafion damage to the ion-conducting sulfonic acid species (>50% loss in sulfur signal) may occur in a relatively short time frame (tens of minutes) depending on the exact nature of the sample and XPS instrument. This motivated the development and validation of a multipoint XPS data acquisition protocol that minimizes Nafion damage, resulting in reliable data acquisition by avoiding significant artifacts from Nafion instability. The developed protocol was then used to analyze both thin film ionomer samples and Pt/C-based CLs. Comparison of PEM fuel cell CLs to Nafion thin films revealed several changes in Nafion spectral features attributed to charge transfer due to interaction with conductive catalyst and support species. This study provides a method to reliably characterize ionomer-containing samples, facilitating fundamental studies of the catalyst-ionomer interface and more applied investigations of structure-processing-performance correlations in PEM fuel cell and electrolyzer CLs.

Colloidal Stability of PFSA-Ionomer Dispersions Part II: Determination of Suspension pH Using Single-Ion Potential Energies

Perfluorosulfonic acid (PFSA) ionomers serve a vital role in the performance and stability of fuel-cell catalyst layers. These properties, in turn, depend on the colloidal processing of precursor inks. To understand the colloidal structure of fuel-cell catalyst layers, we explore the aggregation of PFSA ionomers dissolved in water/alcohol solutions and relate the predicted aggregation to experimental measurements of solution pH. Not all side chains contribute to measured pH because of burying inside particle aggregates. To account for the measured degree of dissociation, a new description is developed for how PFSA aggregates interact with each other. The developed single-counterion electrostatic repulsive pair potential from Part I is incorporated into the Smoluchowski collision-based kinetics of interacting aggregates with buried side chains. We demonstrate that the surrounding solvent mixture affects the degree of aggregation as well as the pH of the system primarily through the solution dielectric permittivity, which drives the strength of the interparticle repulsive energies. Successful pH prediction of Nafion ionomer dispersions in water/n-propanol solutions validates the numerical calculations. Nafion-dispersion pH measurements serve as a surrogate for Nafion particle-size distributions. The model and framework can be leveraged to explore different ink formulations.

Investigating Electrode-Ionomer Interface Phenomena for Electrochemical Energy Applications

The endeavor to develop high-performance electrochemical energy applications has underscored the growing importance of comprehending the intricate dynamics within an electrode's structure and their influence on overall performance. This review investigates the complexities of electrode-ionomer interactions, which play a critical role in optimizing electrochemical reactions. Our examination encompasses both microscopic and meso/macro scale functions of ionomers at the electrode-ionomer interface, providing a thorough analysis of how these interactions can either enhance or impede surface reactions. Furthermore, this review explores the broader-scale implications of ionomer distribution within porous electrodes, taking into account factors like ionomer types, electrode ink formulation, and carbon support interactions. We also present and evaluate state-of-the-art techniques for investigating ionomer distribution, including electrochemical methods, imaging, modeling, and analytical techniques. Finally, the performance implications of these phenomena are discussed in the context of energy conversion devices. Through this comprehensive exploration of intricate interactions, this review contributes to the ongoing advancements in the field of energy research, ultimately facilitating the design and development of more efficient and sustainable energy devices.

Anion Exchange Ionomers: Design Considerations and Recent Advances - An Electrochemical Perspective

Alkaline-based electrochemical devices, such as anion exchange membrane (AEM) fuel cells and electrolyzers, are receiving increasing attention. However, while the catalysts and membrane are methodically studied, the ionomer is largely overlooked. In fact, most of the studies in alkaline electrolytes are conducted using the commercial proton exchange ionomer Nafion. The ionomer provides ionic conductivity; it is also essential for gas transport and water management, as well as for controlling the mechanical stability and the morphology of the catalyst layer. Moreover, the ionomer has distinct requirements that differ from those of anion-exchange membranes, such as a high gas permeability, and that depend on the specific electrode, such as water management. As a result, it is necessary to tailor the ionomer structure to the specific application in isolation and as part of the catalyst layer. In this review, an overview of the current state of the art for anion exchange ionomers is provided, summarizing their specific requirements and limitations in the context of AEM electrolyzers and fuel cells.

Solvent Effects on the Catalyst Ink and Layer Microstructure for Anion Exchange Membrane Fuel Cells

Understanding the complex solvent effects on the microstructures of ink and catalyst layer (CL) is crucial for the development of high-performance anion exchange membrane fuel cells (AEMFCs). Herein, we study the solvent effects within the binary solvent ink system composed of water, isopropyl alcohol (IPA), commercial anion exchange ionomer, and Pt/C catalyst. The results show that the Pt/C particles and ionomer tend to form large aggregates wrapped with a thick ionomer layer in IPA-rich ink and promote the formation of large mesopores within the CL. With the increase of the water content in the ink, Pt/C particles are more likely to bridge to each other through wrapped FAA to form a well-connected three-dimensional network. The CL fabricated using water-rich ink shows smaller pores, higher porosity, and a more homogeneous ionomer network without the formation of large aggregates. Based on these results, we propose that the properties of the solvent mixture, including dielectric constant (ε) and solubility parameter (δ), affect the coulomb interaction of charged particles and surface tension at interfaces, which in turn affects the microstructure of ink and CL. By leveraging the solvent effects, we optimize the CL microstructures and improve the performance of AEMFC. These results may guide the rational design and fabrication of AEMFCs.

Elucidation of Critical Catalyst Layer Phenomena toward High Production Rates for the Electrochemical Conversion of CO to Ethylene

This work utilizes EIS to elucidate the impact of catalyst-ionomer interactions and cathode hydroxide ion transport resistance (RCL,OH-) on cell voltage and product selectivity for the electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for RCL,OH- and ca. a 25% change in electrode porosity. Decreasing RCL,OH- results in improved ethylene Faradaic efficiency (FE), up to ∼57%, decrease in hydrogen FE, by ∼36%, and reduction in cell voltage by up to 1 V at 700 mA/cm2. Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for non-hydrogen products in a 25 cm2 membrane electrode assembly at 700 mA/cm2 and <3 V. Additionally, the implications of optimizing RCL,OH- is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process.

Materials Strategies Tackling Interfacial Issues in Catalyst Layers of Proton Exchange Membrane Fuel Cells

The most critical challenge for the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs), one of the primary hydrogen energy technologies, is to achieve decent output performance with low usage of platinum (Pt). Currently, the performance of PEMFCs is largely limited by two issues at the catalyst/ionomer interface, specifically, the poisoning of active sites of Pt by sulfonate groups and the extremely sluggish local oxygen transport toward Pt. In the past few years, emerging strategies are derived to tackle these interface problems through materials optimization and innovation. This perspective summarizes the latest advances in this regard, and in the meantime unveils the molecule-level mechanisms behind the materials modulation of interfacial structures. This paper starts with a brief introduction of processes and structures of catalyst/ionomer interfaces, which is followed by a detailed review of progresses in key materials toward interface optimization, including catalysts, ionomers, and additives, with particular emphasis on the role of materials structure in regulating the intermolecular interactions. Finally, the challenges for the application of the established materials and research directions to broaden the material library are highlighted.

Structure and conductivity of ionomer in PEM fuel cell catalyst layers: a model-based analysis

Efforts in design and optimization of catalyst layers for polymer electrolyte fuel cells hinge on mathematical models that link electrode composition and microstructure with effective physico-chemical properties. A pivotal property of these layers and the focus of this work is the proton conductivity, which is largely determined by the morphology of the ionomer. However, available relations between catalyst layer composition and proton conductivity are often adopted from general theories for random heterogeneous media and ignore specific features of the microstructure, e.g., agglomerates, film-like structures, or the hierarchical porous network. To establish a comprehensive understanding of the peculiar structure-property relations, we generated synthetic volumetric images of the catalyst layer microstructure. In a mesoscopic volume element, we modeled the electrolyte phase and calculated the proton conductivity using numerical tools. Varying the ionomer morphology in terms of ionomer film coverage and thickness revealed two limiting cases: the ionomer can either form a thin film with high coverage on the catalyst agglomerates; or the ionomer exists as voluminous chunks that connect across the inter-agglomerate space. Both cases were modeled analytically, adapting relations from percolation theory. Based on the simulated data, a novel relation is proposed, which links the catalyst layer microstructure to the proton conductivity over a wide range of morphologies. The presented analytical approach is a versatile tool for the interpretation of experimental trends and it provides valuable guidance for catalyst layer design. The proposed model was used to analyze the formation of the catalyst layer microstructure during the ink stage. A parameter study of the initial ionomer film thickness and the ionomer dispersion parameter revealed that the ionomer morphology should be tweaked towards well-defined films with high coverage of catalyst agglomerates. These implications match current efforts in the experimental literature and they may thus provide direction in electrode materials research for polymer electrolyte fuel cells.

Towards a realistic prediction of catalyst durability from liquid half-cell tests

Liquid half-cell measurements provide a convenient laboratory method for determining relevant parameters of electro-catalysts applied in e.g. polymer electrolyte membrane fuel cells. While these measurements may be effective in certain contexts, their applicability to real-world systems, such as single-cells in a membrane electrode assembly (MEA) configuration, is not always clear. This is particularly true when assessing the stability of these systems through accelerated stress tests (ASTs). Due to different electrode compositions and operating conditions, nanoscale degradation proceeds differently. Nevertheless, given the high demands of MEA measurements in terms of time, testing equipment complexity, and amount of catalyst material, application-relevant predictions of catalyst durability from liquid half-cell tests are highly desirable. This study combines electrochemical and nanoparticle analysis based on transmission electron microscopy to conduct a typical voltage cycling AST for rotating disc electrode (RDE) measurements, showing that the loss of the electrochemically active surface area (ECSA) of the used Pt/Vulcan catalyst is strongly enhanced at 80 °C compared to room temperature, which goes along with increased nanoparticle coarsening. Additionally, a high ionomer/carbon mass ratio (I/C = 0.7) accelerates the ECSA loss, and further investigations of its influence suggest a combination of several factors, including the high local proton concentration and the presence of adsorbing anions. At the same temperature (80 °C) and I/C ratio (0.7), the ECSA loss vs. AST cycle number of the Pt/Vulcan catalyst is essentially identical for a voltage cycling AST conducted in either an RDE half-cell or an MEA configuration, suggesting that liquid electrolyte half-cell based ASTs can provide application-relevant results. Thus, our study points out a way for predicting the stability of electro-catalysts in MEAs based on RDE experiments that require less specialized equipment and only μg-quantities of catalysts.

Humidity-Dependent Hydration and Proton Conductivity of PFSA Ionomer Thin Films at Fuel-Cell-Relevant Temperatures: Effect of Ionomer Equivalent Weight and Side-Chain Characteristics

Studies on the hydration properties, proton conductivity, and water content of perfluorinated ionomer thin films at temperatures relevant to fuel cell operation temperatures (around 80 °C) and the effect of ionomer chemistry are scarce. In this work, we report the water content and proton conductivity properties of thin-film ionomers (30 nm) at 80 °C over a wide range of relative humidity (0-90%) for seven different ionomers differing in the side-chain structure, including the number of protogenic groups, with the equivalent weight ranging from 620 to 1100 g/mol of sulfonic acid. The results show that the acid content or equivalent weight of the ionomer is the strongest determinant of both the swelling and the proton conductivity of ionomer films at a given relative humidity. The molar water content (λ) of ionomer films normalized to the molar protogenic group is observed to be equivalent-weight-dependent, implying that the affinity for water is acid-content-dependent. At high relative humidity conditions (>70%) pertinent to fuel cell operations, the proton conductivity of low-equivalent-weight ionomers was higher than that of higher-equivalent-weight ionomers. However, upon correlating the proton conductivity with molar water content (λ), the differences reduce dramatically, highlighting that water content is the controlling factor for proton conduction. Significantly higher values of both water content and proton conductivity are observed at 80 °C compared to those at 30 °C, implying that room temperature data are not reliable for estimating ionomer properties in the fuel cell catalyst layer.

Impact of Platinum Primary Particle Loading on Fuel Cell Performance: Insights from Catalyst/Ionomer Ink Interactions

A variety of electrochemical energy conversion technologies, including fuel cells, rely on solution-processing techniques (via inks) to form their catalyst layers (CLs). The CLs are heterogeneous structures, often with uneven ion-conducting polymer (ionomer) coverage and underutilized catalysts. Various platinum-supported-on-carbon colloidal catalyst particles are used, but little is known about how or why changing the primary particle loading (PPL, or the weight fraction of platinum of the carbon-platinum catalyst particles) impacts performance. By investigating the CL gas-transport resistance and zeta (ζ)-potentials of the corresponding inks as a function of PPL, a direct correlation between the CL high current density performance and ink ζ-potential is observed. This correlation stems from likely changes in ionomer distributions and catalyst-particle agglomeration as a function of PPL, as revealed by pH, ζ-potential, and impedance measurements. These findings are critical to unraveling the ionomer distribution heterogeneity in ink-based CLs and enabling enhanced Pt utilization and improved device performance for fuel cells and related electrochemical devices.

Effect of Catalyst Ink and Formation Process on the Multiscale Structure of Catalyst Layers in PEM Fuel Cells

The structure of a catalyst layer (CL) significantly impacts the performance, durability, and cost of proton exchange membrane (PEM) fuel cells and is influenced by the catalyst ink and the CL formation process. However, the relationship between the composition, formulation, and preparation of catalyst ink and the CL formation process and the CL structure is still not completely understood. This review, therefore, focuses on the effect of the composition, formulation, and preparation of catalyst ink and the CL formation process on the CL structure. The CL structure depends on the microstructure and macroscopic properties of catalyst ink, which are decided by catalyst, ionomer, or solvent(s) and their ratios, addition order, and dispersion. To form a well-defined CL, the catalyst ink, substrate, coating process, and drying process need to be well understood and optimized and match each other. To understand this relationship, promote the continuous and scalable production of membrane electrode assemblies, and guarantee the consistency of the CLs produced, further efforts need to be devoted to investigating the microstructure of catalyst ink (especially the catalyst ink with high solid content), the reversibility of the aged ink, and the drying process. Furthermore, except for the certain variables studied, the other manufacturing processes and conditions also require attention to avoid inconsistent conclusions.

Slot-die-coating operability windows for polymer electrolyte membrane fuel cell cathode catalyst layers

Roll-to-roll (R2R) slot-die coating of polymer electrolyte membrane fuel cell (PEMFC) catalyst layers represents a scalable deposition method for producing 10-20 m²·min^-1 of catalyst-coated gas diffusion layers (GDLs). This high-throughput production technique will help lower the cost of PEMFC catalyst layers. The uniformity of the wet layer applied by slot die deposition is affected by process parameters such as substrate speed, vacuum pressure applied at the upstream meniscus, gap between the slot die lips and substrate, ink rheology, and other ink and substrate properties. The set of conditions for producing a defect-free coating with a dilute ink typically requires little to no upstream vacuum pressure, so suitable operating conditions can be found easily through trial and error and operator intuition. However, the higher viscosity of more concentrated inks dramatically shifts the range of settings that result in a homogeneous coating to higher vacuum levels, which are harder to find through hit or miss. A predictive model showing the range of operable conditions decreases material wastage inherent in experimentally searching for suitable parameters. In this study, the defect-free coating parameter window is explored experimentally and theoretically for two concentrations of PEFC cathode inks. Both a full capillary hydrodynamic model and a computationally cheaper viscocapillary model successfully predict the experimentally determined coating window within the experimental and model uncertainty limits for inks with 5.3 wt% and 12.0 wt% solids ink while maintaining the 0.1 mg_Pt·cm^-2Pt areal loading target. This paper demonstrates a viable pathway for meeting the $30/kW_net ultimate cost target of the United States Department of Energy (U.S. DOE) Hydrogen Fuel Cells Technologies Office (HFTO). The concentrated ink lowers the thermal energy and capital expenditure (CapEx) budget of the coating process by decreasing the amount of time, energy, and floorspace required for drying the coating.

Linking Perfluorosulfonic Acid Ionomer Chemistry and High-Current Density Performance in Fuel-Cell Electrodes

Transport phenomena are key in controlling the performance of electrochemical energy-conversion technologies and can be highly complex, involving multiple length scales and materials/phases. Material designs optimized for one reactant species transport however may inhibit other transport processes. We explore such trade-offs in the context of polymer-electrolyte fuel-cell electrodes, where ionomer thin films provide the necessary proton conductivity but retard oxygen transport to the Pt reaction site and cause interfacial resistance due to sulfonate/Pt interactions. We examine the electrode overall gas-transport resistance and its components as a function of ionomer content and chemistry. Low-equivalent-weight ionomers allow better dissolved-gas and proton transport due to greater water uptake and low crystallinity but also cause significant interfacial resistance due to the high density of sulfonic acid groups. These effects of equivalent weight are also observed via in situ ionic conductivity and CO displacement measurements. Of critical importance, the results are supported by ex situ ellipsometry and X-ray scattering of model thin-film systems, thereby providing direct linkages and applicability of model studies to probe complex heterogeneous structures. Structural and resultant performance changes in the electrode are shown to occur above a threshold sulfonic-group loading, highlighting the significance of ink-based interactions. Our findings and methodologies are applicable to a variety of solid-state energy-conversion devices and material designs.

Effects of Ink Formulation on Construction of Catalyst Layers for High-Performance Polymer Electrolyte Membrane Fuel Cells

Rational design of catalyst layers in a membrane electrode assembly (MEA) is crucial for achieving high-performance polymer electrolyte membrane fuel cells. Establishing a clear understanding of the property (catalyst ink)-structure (catalyst layer)-performance (MEA) relationship lays the foundation for this rational design. In this work, a synergistic approach was taken to correlate the ink formulation, the microstructure of catalyst layers, and the resulting MEA performance to establish such a property-structure-performance relationship. The solvent composition (n-PA/H₂O mixtures) demonstrated a strong influence on the performance of the MEA fabricated with an 830-EW (Aquivion) ionomer, especially polarization losses of cell activation and mass transport. The performance differences were studied in terms of how the solvent composition affects the catalyst/ionomer interface, ionomer network, and pore structure of the resulting catalyst layers. The ionomer aggregates mainly covered the surface of catalyst aggregates acting as oxygen reduction reaction active sites, and the aggregate sizes of the ionomer and catalyst (revealed by ultrasmall angle X-ray scattering and cryo-transmission electron microscopy) were dictated by tuning the solvent composition, which in turn determined the catalyst/ionomer interface (available active sites). In n-PA/H₂O mixtures with 50∼90 wt % H₂O, the catalyst agglomerates could be effectively broken up into small aggregates, leading to enhanced kinetic activities. The boiling point of the mixed solvents determined the pore structure of ultimate catalyst layers, as evidenced by mercury porosimetry and scanning electron microscopy. For mixed solvents with a higher boiling point, the catalyst-ionomer aggregates in the ink tend to agglomerate during the solvent evaporation process and finally form larger catalyst-ionomer aggregates in the ultimate catalyst layer, resulting in more secondary pores and thus lower mass transport resistance. Both the enlarged catalyst/ionomer interface and appropriate pore structure were achieved with the catalyst layer fabricated from an n-PA/H₂O mixture with 90 wt % H₂O, leading to the best MEA performance.

Distinguishing Adsorbed and Deposited Ionomers in the Catalyst Layer of Polymer Electrolyte Fuel Cells Using Contrast-Variation Small-Angle Neutron Scattering

The ionomers distributed on carbon particles in the catalyst layer of polymer electrolyte fuel cells (PEFCs) govern electrical power via proton transport and oxygen permeation to active platinum. Thus, ionomer distribution is a key to PEFC performance. This distribution is characterized by ionomer adsorption and deposition onto carbon during the catalyst-ink coating process; however, the adsorbed and deposited ionomers cannot easily be distinguished in the catalyst layer. Therefore, we identified these two types of ionomers based on the positional correlation between the ionomer and carbon particles. The cross-correlation function for the catalyst layer was obtained by small-angle neutron scattering measurements with varying contrast. From fitting with a model for a fractal aggregate of polydisperse core-shell spheres, we determined the adsorbed-ionomer thickness on the carbon particle to be 51 Å and the deposited-ionomer amount for the total ionomer to be 50%. Our technique for ionomer differentiation can be used to optimally design PEFC catalyst layers.

Impact of the Composition of Alcohol/Water Dispersion on the Proton Transport and Morphology of Cast Perfluorinated Sulfonic Acid Ionomer Thin Films

The dispersion of perfluorinated sulfonic acid ionomers in catalyst inks is an important factor that controls the performance of catalyst layers in membrane electrode assemblies of polymer electrolyte fuel cells. Herein, the effects of water/alcohol compositions on the morphological properties and proton transport are examined by grazing incidence small-angle X-ray scattering, grazing incidence wide-angle X-ray scattering, and electrochemical impedance spectroscopy. The thin films cast by a high water/alcohol ratio Nafion dispersion have high proton conductivity and well-defined hydrophilic/hydrophobic phase separation, which indicates that the proton conductivity and morphology of the Nafion thin films are strongly influenced by the state of dispersion. This finding is expected to further understand the morphology and proton transport properties of Nafion thin films with different water/alcohol ratios, which has implications for the performance of the Pt/Nafion interface.

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe-N-C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells

We present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe-N-C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1-propanol (nPA). The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (H₂O %) in the DM on the ink microstructure were studied. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks. In the absence of the ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure for catalyst concentrations as low as 2 wt %. The effect of H₂O % in the DM on particle agglomeration was found to vary with particle concentration. In concentrated inks (≥2 wt % catalyst), increasing H₂O % was found to increase agglomeration because of the hydrophobic nature of the catalysts. In dilute inks (<1 wt % catalyst), the trend was reversed with increasing H₂O %, suggesting that electrostatic interactions are dominating the behavior. In inks with 5 wt % catalyst, the addition of an ionomer was found to significantly stabilize the catalyst against agglomeration. Maximum stability was observed at 0.35 I/C for all DM H₂O % studied. At high ionomer concentrations (I/C > 0.35), interesting differences were observed between nPA-rich inks (H₂O % ≤ 50%) and H₂O-rich (82% H₂O) inks. The nPA-rich inks remained predominantly stable-ink viscosity only weakly increased with I/C and the Newtonian behavior was maintained for I/C up to 0.9. In contrast, the H₂O-rich inks exhibited a significant increase in viscoelasticity with increasing I/C, suggesting flocculation of the catalyst by the ionomer. These differences suggest that the nature of the interactions between the ionomer and catalyst is highly dependent on the H₂O % in the DM.

Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly(ionic liquid) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells

Polymer electrolyte membrane fuel cell (PEMFC) electrodes with a 0.07 mgPt cm-2 Pt/Vulcan electrocatalyst loading, containing only a sulfonated poly(ionic liquid) block copolymer (SPILBCP) ionomer, were fabricated and achieved a ca. 2× enhancement of kinetic performance through the suppression of Pt surface oxidation. However, SPILBCP electrodes lost over 70% of their electrochemical active area at 30% RH because of poor ionomer network connectivity. To combat these effects, electrodes made with a mix of Nafion/SPILBCP ionomers were developed. Mixed Nafion/SPILBCP electrodes resulted in a substantial improvement in MEA performance across the kinetic and mass transport-limited regions. Notably, this is the first time that specific activity values determined from an MEA were observed to be on par with prior half-cell results for Nafion-free Pt/Vulcan systems. These findings present a prospective strategy to improve the overall performance of MEAs fabricated with surface accessible electrocatalysts, providing a pathway to tailor the local electrocatalyst/ionomer interface.