Oxygen Transport Resistance Research Articles

A design of gas diffusion media for polymer electrolyte membrane fuel cell: Characterization and water management investigation

Higher power density is a key technological goal for the deployment of polymer electrolyte membrane fuel cells (PEMFCs) in vehicles. Water production is proportional to current density and at high current densities water flooding in catalyst layers can result in significant mass transport limitations. A novel perfluoropolymers material, Teflon™ AF, is introduced as a hydrophobic agent to fabricate microporous layers (MPLs). The MPL ink with varying proportions of Teflon™ AF and Vulcan XC-72 carbon black is prepared and used to coat MPLs into the gas diffusion layers. X-ray computed tomography and mercury intrusion porosimetry are used to characterize the physical properties of the penetrated GDM. The performance of cells with the homemade MPLs are compared with commercial GDM cells under dry and wet operating conditions using varying backpressures. The results at high relative humidity and high backpressure show that the cells with homemade MPLs have less flooding than that with commercial GDM. Oxygen transport resistance measurements using the limiting current method show that the penetration of the MPL into the substrate has an undesirable effect of increasing oxygen transport resistance. The results are of benefit to understanding the water management and gas transport mechanism of MPL for fuel cells operating at both dry and wet conditions.

Electrode microstructure design to improve effective utilization of Fe-N/C catalysts towards oxygen reduction reaction process

Fe-N/C materials have shown intrinsic activities comparable to Pt/C catalysts for oxygen reduction reaction on rotating ring-disk electrodes (RRDE). However, due to the insufficient three-phase interfaces (TPIs) and high oxygen transport resistance (RT), the high intrinsic activity cannot be sufficiently utilized in electrodes, resulting in a gap between the intrinsic catalytic activity on RRDE and the performance in devices. To expand the TPIs and promote oxygen transport, a novel electrode with a transition layer structure is proposed to disperse the active sites. The dispersion degree of active sites is optimized by tuning the solid–liquid interfacial energy between the ink solvent and the substrate. A high electrochemical active area of 1264 cm2 and a low RT of 2.0 s cm−1 are achieved for the electrode prepared by an alcohol-rich ink. The simulation and experimental results demonstrate that the microstructure can benefit the extension of TPIs and facilitate oxygen transport in the air cathode, ultimately achieving efficient utilization of catalytic activities. A maximum power density of 35.4 mW cm−2 is achieved in a membrane-less direct formate fuel cell, surpassing most congeneric devices. Our approach clarifies the relationship between TPI construction, mass transport, and electrode microstructure, which successfully exploits the intrinsic activity on air cathodes and improves the power generation ability.

Local oxygen transport resistance in polymer electrolyte fuel cells: origin, dependencies and mitigation

Next-generation polymer electrolyte fuel cells (PEFCs) require an integral design of the porous structure of electrodes at different scales to improve performance and enlarge durability while reducing cost. One of today’s biggest challenges is the stable, high-performance operation at low Pt loading due to the detrimental effect of the local oxygen transport resistance caused by ionomer around catalyst sites. Hindered local oxygen transport arises from sluggish kinetics at the local reaction environment, that comprises adsorption at (wet) ionomer and Pt interfaces, and diffusivity of gas species in ionomer and water. Diverse factors affect oxygen transport, including operating conditions (relative humidity, temperature, and pressure), ionomer content and morphology, ionomer heterogeneity, porosity of carbon support, catalyst dispersity, and flooding. To attain performance and durability targets, it is essential to maximize the oxygen utilization of the catalyst layer by implementing enhanced membrane electrode assembly architectures. This involves employing advanced catalyst layer preparation techniques, including electrospraying, to generate optimized highly porous morphologies. Furthermore, achieving these targets necessitates the development of new materials with tailored properties, such as high permeability and porous ionomers, among other innovative strategies.

Experimental and Numerical Simulation Study of Oxygen Transport in Proton Exchange Membrane Fuel Cells at Intermediate Temperatures (80 °C-120 °C).

Investigating the oxygen transport law within the Membrane Electrode Assembly at intermediate temperatures (80-120 °C) is crucial for enhancing fuel cell efficiency. This study analyzed the resistance to oxygen transport within the Membrane Electrode Assembly at intermediate temperatures using limiting current density and electrochemical impedance spectroscopy. The study findings reveal that, as temperature progressively increases, the Ostwald ripening effect leads to a 34% rise in the local oxygen transport resistance (Rlocal) in relation to the pressure-independent resistance (Rnp) within the cathode catalytic layer. Concurrently, the total transport resistance (Rtotal) decreases from 27.8% to 37.5% due to an increase in the gas diffusion coefficient and molecular reactivity; additionally, there is a decrease in the amount of liquid water inside the membrane electrode. A three-dimensional multiphysics field steady-state model was also established. The model demonstrates that the decrease in oxygen partial pressure can be mitigated effectively by increasing the back pressure at intermediate temperatures to ensure the cell's performance.

Synthesis of a Mesoporous SnO2 Catalyst Support and the Effect of Its Pore Size on the Performance of Polymer Electrolyte Fuel Cells.

The aim of this study was to clarify the effectiveness and challenges of applying mesoporous tin oxide (SnO2)-based supports for Pt catalysts in the cathodes of polymer electrolyte fuel cells (PEFCs) to simultaneously achieve high performance and high durability. Recently, the focus of PEFC application in automobiles has shifted to heavy-duty vehicles (HDVs), which require high durability, high energy-conversion efficiency, and high power density. It has been reported that employing mesoporous carbon supports improves the initial performance by mitigating catalyst poisoning caused by sulfonic acid groups of the ionomer as well as by reducing the oxygen transport resistance through the Pt/ionomer interface. However, carbon materials in the cathode can degrade oxidatively during long-term operation, and more stable materials are desired. In this study, we synthesized connected mesoporous Sb-doped tin oxides (CMSbTOs) with controlled mesopore sizes in the range of 4-11 nm and tested their performance and durability as cathode catalyst supports. The CMSbTO supports exhibited higher fuel cell performance at a pore size of 7.3 nm than the solid-core SnO2-based, solid-core carbon, and mesoporous carbon supports under dry conditions, which can be attributed to the mitigation of the formation of the Pt/ionomer interface and the better proton conductivity within the mesopores even at the low-humidity conditions. In addition, the CMSbTO supports exhibited high durability under oxidative conditions. These results demonstrate the promising applicability of mesoporous tin oxide supports in PEFCs for HDVs. The remaining challenges, including the requirements for improving performance under wet conditions and stability under reductive conditions, are also discussed.

Patterned hydrophobic gas diffusion layers for enhanced water management in polymer electrolyte fuel cells

Flooding of the cathode due to water accumulation is one of the biggest limiting factors in the performance of polymer electrolyte fuel cells (PEFCs). This study therefore attempts to solve this issue by fabricating gas diffusion layers (GDLs) with differently patterned hydrophobic regions. The GDLs in three different patterns (triangular, diamond, and inverted-triangular) were prepared by brushing a Polytetrafluoroethylene (PTFE) solution onto commercial carbon papers through a mask and tested in PEFCs. The patterned GDLs results in superior performance in all cases compared to a uniformly PTFE-treated GDL. Notably, the oxygen transport resistance is significantly reduced, indicating that the water accumulation in the cathode is avoided. This is attributed to the patterned hydrophobicity gradient providing distinct pathways for water and oxygen. The GDL with triangular patterning displays the highest peak power density, due to the fact that the untreated less hydrophobic region is in direct contact with the cathode outlet in this case, facilitating the removal of excess liquid water. Overall, the study confirms that the GDLs with patterned hydrophobicity could be used to enhance the performance of commercial PEFC systems by facilitating water management, potentially leading to improved efficiency and durability.

Boosting Bulk Oxygen Transport with Accessible Electrode Nanostructure in Low Pt Loading PEMFCs.

Despite the high potential for reducing carbon emissions and contributing to the future of energy utilization, polymer electrolyte membrane fuel cells (PEMFCs) face challenges such as high costs and sluggish oxygen transport in cathode catalyst layers (CCLs). In this study, the impact of pore size distribution on bulk oxygen transport behavior is exploredby introducing nano calcium carbonate of varying particle sizes for pore-forming. Physicochemical characterizationsfor are employed to examine the electrode structure, while in situ electrochemical measurements are used to scrutinize bulk oxygen transport resistance, effective oxygen diffusivity ( ) and fuel cell performance. Additionally, the CCLs are constructed with aid of Lattice Boltzmann method (LBM) simulations and for CCLs with different pore size distribution are calculated. The findings reveal that initially increases and then decreases as the most probable pore size increases. A "sphere-pipe" model is proposed to describe practical bulk oxygen transport in CCLs, highlighting the significant role of not only the pore size of secondary pores but also the number of primary pores in bulk oxygen transport.

Research of Proton Exchange Membrane Fuel Cell Modeling on Concentration Polarization under Variable-Temperature Operating Conditions

In this study, a concentration overvoltage model that focuses on describing variable-temperature operating condition properties for PEMFCs is established. Sensitivity analysis and a quantification study of oxygen transport resistance are carried out based on the oxygen transport resistance model and measurement data. By analyzing the influence of temperature on cathode oxygen transport resistance, the key structural parameters of the cathode oxygen transport resistance models are estimated, and the parameter modification method of fuel cell limiting current density under variable temperatures is proposed. Based on the polarization curve test experiments under variable-temperature conditions, it is demonstrated that the newly developed concentration overvoltage model reduces the relative error of simulation for a low Pt loading fuel cell in the high current region by 2.97% and 10.06% at 60 °C and 80 °C, respectively. The newly established concentration overvoltage model of a PEMFC solves the problem that the parameter of limiting current density is set without considering the influence of fuel cell temperature fluctuation, which leads to the poor simulation accuracy of the concentration overvoltage model in the high current region.

Investigating the transient electrical behaviors in PEM fuel cells under various platinum distributions within cathode catalyst layers

The spatial distribution of platinum (Pt) within the cathode catalyst layer (CCL) is vital for the electrochemical reactions and mass transport in fuel cells. Though important, the transient effects of these distributions are seldom explored. This study examines the impact of Pt distribution on transient electrical behaviors, including voltage and local current distribution (LCD) uniformity, using a transient, two-dimensional, two-phase, non-isothermal fuel cell model that incorporates catalyst agglomerate. Three Pt distribution types are investigated: uniform, MPL-side biased, and PEM-side biased. Results indicate a voltage undershoot occurs during current loading. Compared to the homogeneous CCL, PEM-side bias reduces this undershoot by 12.5% due to shortened proton transfer paths and decreased ohmic loss, while MPL-side bias increases it by 18.8% due to the inverse effect. Additionally, Pt distribution affects both oxygen transport and reaction resistance within the agglomerate, influencing LCD uniformity. Under loading conditions, gradient CCLs show inferior LCD uniformity than homogeneous ones. Peak non-uniformity values of 0.22, 0.59, and 0.71 are observed for homogeneous, MPL-biased, and PEM-biased CCLs, respectively. From the perspective of voltage and LCD uniformity, the MPL-side biased CCL is not found to enhance dynamic characteristics, whereas the PEM-side bias improves voltage undershoot but at the cost of LCD uniformity. This study provides a novel perspective on fuel cell dynamics, emphasizing the transient effects of Pt distribution and their potential for optimizing dynamic performance by adjusting the Pt gradient.

A Rheo-Impedance investigation on the interparticle interactions in the catalyst ink and its impact on electrode network formation in a proton exchange membrane fuel cell

The performance of a proton exchange membrane fuel cell is highly dependent on the microstructure of the catalyst layer. The catalyst layer consists of a network of platinum supported by carbon particles mixed with an ion-conductive ionomer. Optimum coverage of ionomer on catalyst is essential in providing proton conductive pathways while maintaining minimal oxygen transport resistance. Considering that most of the catalyst and ionomer interactions occur as a result of ink formulation and evolution during the high-shear coating process, a new methodology involving a combination of ink flow properties and electrochemical impedance spectroscopy is introduced to study interparticle interactions in catalyst ink. Five ink samples with ionomer-to-carbon ratios ranging from 0 to 1 are used to investigate the interplay between ionomer and catalyst. The flow and impedance properties of the ink are measured simultaneously to investigate the agglomerate characteristics and the percolation of conductive catalyst in the catalyst ink, while fixing the carbon to solvent ratio. This study successfully demonstrate the effectiveness of the newly developed characterization tools, which can be used for evaluating new materials and processing parameters. The insights gained from this study can be applied to optimize the triple-phase-boundaries and form efficient electrode structure with low Pt loading to enhance overall fuel cell performance.

Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells.

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

Engineering Triple‐Phase Boundary in Pt Catalyst Layers for Proton Exchange Membrane Fuel Cells

AbstractEngineering triple‐phase boundaries in low Pt‐loaded catalyst layers is highly desired yet challenging due to the poor Pt utilization caused by inhomogeneous Nafion ionomer coverage over catalyst nanoparticles and high mass transport resistance near catalyst surface. Herein, an effective Pt catalyst/support design strategy by using urea to modify the carbon supports is reported, in which the balance between nitrogen doping and Pt nanoparticle deposition can be well achieved without sacrificing catalyst performance. The nitrogen‐modified carbon with the positively charged surface can electrostatically attract with ionomer with negative charges in a catalyst ink. Meanwhile, ionomer can be preserved into a solid catalyst layer, forming a desirable ionomer/catalyst interface with improved dry proton accessibility and lowered oxygen transport resistance. Consequently, this interface leads to striking performance improvement in the kinetic and mass transport regions in the membrane electrode assembly level, with the current density of 1.11 A cm−2 at 0.65 V under 50% RH and 85 °C operating conditions, reaching 2.8 times this value compared with the one without modification.

An improved agglomerate model with adsorption isotherm for oxygen transport in CCLs with low Pt loading

Understanding of oxygen transport in cathode catalyst layers with low Pt loading is of great importance to the proton exchange membrane fuel cells. The resistance to oxygen transport within the catalyst layers (CCLs) increases significantly as the Pt loading decreases. Thus, it is necessary to develop an accurate continuum-scale model for the oxygen transport and reaction in catalyst layers with low Pt loading so as to guide the optimization of catalyst layers. To address this issue, a modified agglomerate model is developed in the present study. In the model, the CCLs are conceptualized as packings of agglomerate particles composed of the carbon, ionomer, and catalyst. Each of agglomerate particle is covered by a thin layer of ionomer. The main features of our model are two folds: (1) adsorption isotherm is employed instead of Henry's law, commonly used the previous agglomerate models, to depict the oxygen adsorption at the surface of ionomer; (2) non-uniform oxygen transfer flux across the ionomer layer surrounded each agglomerate is considered. The results predicted by our developed model are in good agreement with the experimental data for the polarization curve and the variations of the oxygen transport resistance with the Pt loadings. Especially, our model is superior to the previous agglomerate models in regarding to the variation of oxygen transport resistance with mass fraction of Pt in the catalyst. The modified agglomerate model developed in this work provides an effective tool for investigation of oxygen transport and reaction in CCLs with low Pt loading.

Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layers for Performance Enhancement of Polymer Electrolyte Fuel Cells

A novel microporous layer (MPL) coated gas diffusion layer (GDL) is developed to improve water management of polymer electrolyte fuel cells (PEFCs) by incorporating hydrophobic and hydrophilic pores within the same layer. This MPL expels excess water at the interface between the catalyst layer and MPL through hydrophilic pores while maintaining efficient oxygen transport through hydrophobic pores, reducing oxygen transport resistance under high humidity conditions. The water permeability and relative oxygen permeance tests demonstrate the presence of separate hydrophobic and hydrophilic pores in the appropriate composite MPL. The effects of combinations of hydrophilic and hydrophobic binders used in the composite MPLs on the oxygen transport resistance are evaluated. The hydrophobic polytetrafluoroethylene (PTFE) binder and the hydrophilic polyvinyl alcohol (PVA) binder cannot enhance performance due to mismatched sintering temperatures. Although the hydrophobic polyvinylidene fluoride (PVDF) and PVA binders have the same sintering temperature, the performance was degraded due to the strong hydrophilicity of PVA. Another combination of composite MPL incorporates hydrophobic PVDF and Nafion binders. Hydrophilic TiO2 particles are introduced in the Nafion binder to reinforce the hydrophilicity. The appropriate composite MPL significantly reduced the total oxygen transport resistance compared to those obtained with the hydrophobic MPL.

Effect of Engineered Cracks in Catalyst Layers on PEMFC Catalyst Layer Durability

Proton exchange membrane fuel cells (PEMFCs) are expected to play a pivotal role in decarbonizing the transportation sector, and particularly heavy-duty vehicles (HDVs). However, improvements in durability are needed for PEMFCs to compete with state-of-the-art power sources for HDVs. Here, we examine how catalyst layer (CL) cracks that are engineered affect the CL durability by using patterned silicon templates to control the CL crack density at the micrometer scale. Electrochemical analyses show that the initial PEMFC performance is relatively unaffected by crack density, but the performance after durability testing was strongly affected. Specifically, CLs with high crack density showed higher performance relative to CLs without cracks after application of a carbon corrosion accelerated stress test. Electrochemical analyses coupled with X-ray computed tomography and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy showed that the cracks provide shorter oxygen diffusion pathways to reaction sites, leading to decreased oxygen transport resistance. Additionally, we observed that the catalyst durability is unaffected by cracks. Our results provide a mechanistic explanation of the role of cracks in CL durability.

Revealing local oxygen transport in ionomer films on multidimensional nanoscale catalysts in fuel cells

The one-dimensional nanowire Pt-based catalysts achieves a much lower local oxygen transport resistance than three-dimensional catalysts owing to the broader and shorter transport paths in well-layered ionomer films on one-dimensional catalysts.

Linking the ionomer film morphology and nanoscale oxygen transport properties in fuel cells

Transport processes are crucial for the performance of electrochemical energy conversion devices and attract wide attentions. This work focuses on the critical oxygen transport process in the ionomer electrolyte film on a Pt electrode, which highly limits the performance of low Pt-loading fuel cells. Reduction of oxygen transport resistance may be achieved by optimizing the ionomer film morphology. Therefore, the relationship between ionomer film morphology and oxygen transport characteristics is explored by altering ionomer side chain lengths in this work. The results show that the swollen structure with larger water agglomerates in the ionomer film with shorter ionomer side chains is detrimental to the formation of oxygen transport paths. However, the multilamellar structure with an alternating alignment of water agglomerates and PFSA ionomer agglomerates in the ionomer film with longer ionomer side chains has a larger water-PFSA interface, which provides more oxygen transport paths and thus reduces the oxygen transport resistance. This work inspires the novel design concept of the ionomer electrolyte film with low local oxygen transport resistance, i.e., enlarging the water-PFSA interface parallel to the oxygen transport direction via altering the ionomer material properties, which is valuable for the development of low Pt-loading fuel cells.

Unraveling the Effects of Carbon Corrosion on Oxygen Transport Resistance in Low Pt Loading Proton Exchange Membrane Fuel Cells.

Cost and durability have become crucial hurdles for the commercialization of proton exchange membrane fuel cells (PEMFCs). Although a continuous reduction of Pt loading within the cathode catalyst layers (CCLs) can lead to cost savings, it also increases the oxygen transport resistance, which is further compounded by key material degradation. Hence, a further understanding of the mechanism of significant performance loss due to oxygen transport limitations at the triple phase boundaries (TPBs) during the degradation process is critical to the development of low Pt loading PEMFCs. The present study systematically investigates the impact of carbon corrosion in CCLs on the performance and oxygen transport process of low Pt loading PEMFCs through accelerated stress tests (ASTs) that simulate start-up/shutdown cycling. A decline in peak power density from 484.3 to 251.6 mW cm-2 after 1500 AST cycles demonstrates an apparent performance loss, especially at high current densities. The bulk and local oxygen transport resistances (rbulk and Rlocal) of the pristine cell and after 200, 600, 1000, and 1500 AST cycles are quantified by combining the limiting current method with a dual-layer CCL design. The results show that rbulk increased from 1527 to 1679 s cm-2, Rlocal increased from 0.38 to 0.99 s cm-1, and the local oxygen transport resistance with the normalized Pt surface area (rlocal) exhibited an increase from 18.5 to 32.0 s cm-1, indicating a crucial impact on the structure collapse and changes in the chemical properties of the carbon supports in the CCLs. Further, the interaction between the ionomer and carbon supports during the carbon corrosion process is deeply studied via electrochemical quartz crystal microbalance and molecular dynamics simulations. It is concluded that the oxygen-containing functional groups on the carbon surface could impede the adsorption of ionomers on carbon supports by creating an excessively water-rich layer, which in turn aggravates the formation of ionomer agglomerations within the CCLs. This process ultimately leads to the destruction of the TPBs and hinders the transport of oxygen through the ionomer.

The Impact of Mesopores of SnO2 Catalyst Support on the Performance of Polymer Electrolyte Fuel Cells

Recently, the focus of future polymer electrolyte fuel cell (PEFC) application for automobiles has shifted from the class of passenger light-duty vehicles (LDVs) to that of heavy-duty vehicles (HDVs). The total operating time in the lifetime of HDVs is much longer than that of LDVs. Thus, durability is becoming more and more important for the cell components including the catalyst materials, and the compatibility between initial performance and durability at a high level is desired. Employing mesoporous carbons as catalyst supports is a promising option to enhance the initial performance [1]. In the catalyst layer of a PEFC with mesoporous carbon support, Pt-based catalyst nanoparticles deposited inside the mesopores are not directly covered by ionomer. As a result, a catalyst poisoning by sulfonic acid groups of the ionomer is hindered and a high catalytic activity is obtained. In addition, a high oxygen transport resistance thorough Pt/ionomer interfaces [2] can be mitigated by employing mesoporous carbon support. Nonetheless, from the viewpoint of thermodynamics, carbon support can oxidatively degrade during the long-term operation. Tin oxide (SnO2) is one of the promising candidates for substituting the carbon support because of its high electrochemical stability at high potentials [3]. However, to our best knowledge, the mitigation of the ionomer adsorption on the Pt surface by using mesoporous SnO2 support has not been studied in previous works. In this study, we synthesized mesoporous SnO2 supports and investigated the impact of the mesopore on the performance of the PEFC. Connected mesoporous Sb-doped SnO2 particles (CMSbTOs) were synthesized by using a mesoporous carbon as a template (Figure (a)). The size of the mesopore was successfully controlled in the range of 4 – 10 nm by adjusting the carbon template structure and calcination temperature (Figure (b)). The BET surface area and conductivity of the CMSbTOs were in the ranges of 90 – 210 m2 g-1 and ca. 10-2 S cm-1, respectively. Pt nanoparticles were deposited on the CMSbTOs via a colloidal method to obtain Pt/CMSbTO catalyst (Pt loading of 20 wt.%). It was confirmed that the Pt nanoparticles were located both on the outer surface and inside the mesopores of the CMSbTOs by scanning transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) analysis. A membrane electrode assembly (MEA) was fabricated by using a Pt/CMSbTO catalyst for the cathode catalyst layer and single cell tests were performed under dried (30%RH, 82 °C) and highly humidified (80%RH, 60 °C) conditions. In addition, a homemade Pt/Sb-SnO2 catalyst with solid-core SnO2 support and a commercial Pt/Vulcan catalyst (TEC10V30E, TKK) were also tested for comparison. Under the dried conditions, the Pt/CMSbTO catalyst showed a better I-V performance than the Pt/Sb-SnO2 (solid) catalyst and Pt/Vulcan catalyst (Figure (c)). The oxygen reduction reaction (ORR) activity of the Pt/CMSbTO catalyst at 0.84 V was higher than that of the Pt/Sb-SnO2 (solid) and Pt/Vulcan catalysts. This result suggests that catalyst poisoning by the ionomer is mitigated when the mesoporous SnO2 support is employed. Moreover, the local oxygen transport resistance (oxygen transport resistance that is independent of the total gas pressure) of the Pt/CMSbTO catalyst was lower than that of the Pt/Sb-SnO2 (solid) and Pt/Vulcan catalysts, probably because of a decrease in the oxygen transport resistance due to Pt/ionomer interfaces. In contrast, under the highly humidified conditions, the I-V performance of the Pt/CMSbTO catalyst was comparable to that of the Pt/Sb-SnO2 (solid) catalyst and slightly lower than that of the Pt/Vulcan catalyst (Figure (d)). This result can be ascribed to floodings inside the mesopores of the CMSbTO support. Accelerated stress tests (repeated potential steps between 1.0 – 1.5 V under 100%RH, 80 °C) were also performed to confirm the electrochemical stability of the Pt/CMSbTO catalyst at high potentials. The Pt/CMSbTO catalyst showed a much higher retention rate of the electrochemical Pt surface area (ECSA) than the Pt/Vulcan catalyst as expected. More details, including the effect of the pore size of the CMSbTO support on the initial performance, will be discussed in the presentation.