Dissolution Resistance Research Articles

Beneficial role of retained austenite in pitting corrosion resistance of Fe-C-Si-Mn steel in chloride environments

The pitting corrosion behavior of Fe-0.39C-1.51Si-2.01Mn steel was investigated in NaCl-containing boric-borate buffers at pH 7.0. The microstructure of the steel was confirmed to consist of retained austenite and bainite matrix, and the interstitial C concentration in the retained austenite was estimated to be higher than that in the matrix. The results of immersion tests clarified that the retained austenite hardly dissolved in the early stage of pitting, and acted as a barrier against pit propagation. The dissolution resistance of the retained austenite appeared to originate from the high amount of interstitial C.

Galvanic Corrosion of AA5083/Fe in Diluted Synthetic Seawater: Effect of Anodizing on Local Electrochemistry on and around Al 6 (Fe,Mn) on Al-Matrix

In 100-times diluted synthetic seawater at 298 K (pH 8.2), the effect of anodizing on the galvanic corrosion resistance of AA5083 coupled to pure Fe, Type 430, or 304 stainless steel was investigated by measuring the galvanic current densities and electrode potentials. Anodizing in H 2 SO 4 effectively suppressed the galvanic corrosion of AA5083. It was shown that an increase in pitting potential by anodizing alone could not determine whether galvanic corrosion would occur or not. The cathodic activity on Al 6 (Fe, Mn), which causes alkalization on and around Al 6 (Fe, Mn) particles, decreased as the anodizing time and voltage increased. And, the anodic oxide film on the Al-matrix in alkaline environments became stable as the thickness of the oxide film increased. A comparison of these two factors revealed that the dissolution resistance of surface oxide film on Al-matrix contributed the galvanic corrosion prevention of anodized AA5083 coupled to pure Fe. In the case of AA5083 anodized at 16 V for 180 s, no galvanic corrosion damage was observed on the AA5083 coupled to Type 430 or 304.

First-Principles Investigation on Work Function of Martensitic Carbon Steels: Effect of Interstitial Carbon on Anodic Dissolution Resistance

The effect of interstitial carbon on the work function and the dissolution resistance of martensitic carbon steels was investigated. Ultraviolet photoelectron spectroscopy measurements of 0.001%C, 0.44%C, and 0.88%C specimens showed that the work function of steels increased with the amount of interstitial carbon. In addition, first-principles calculations indicated that the presence of interstitial carbon clearly increased the work function on both the (110) and (100) orientation surfaces. The immersion tests and potentiodynamic polarization measurements of the specimens were conducted in 50 mM C 8 H 5 KO 4 at pH 4.0, and it was clarified that the anodic dissolution reaction was suppressed as the amount of interstitial carbon increased. The improvement in work function appeared to be related to the superior anodic dissolution resistance.

Experimental Evaluation of PEFC Catalyst Layer Structure to Reduce Oxygen Transport Resistances

In polymer electrolyte fuel cells (PEFCs), it is required to reduce the amount of Pt used in the cathode catalyst layer (CL). With the CLs at lower Pt loading, it has been reported that the oxygen transport resistance drastically increases. Our previous research (1) evaluated the components of oxygen transport resistance for CLs fabricated with various structure and reported that the resistance at the Pt surface was dominant while the resistance of oxygen dissolution into the ionomer was negligible. This study focuses on CLs with low Pt loadings. We try to elucidate the appropriate CL structure with lower oxygen transport resistance based on our quantitative evaluation.In this study, catalyst coated membranes were fabricated with various cathode structure. Three types of Pt-supported carbons (TEC10E20E, TEC10E30E, TEC10E50E) having different Pt carrying densities were used. The ratios of Pt to carbon (Pt carrying density) are approximately 20,30 and 50 wt% respectively. The ratios of ionomer to carbon were set with I/C = 0.8.To evaluate the total oxygen transport resistance and its components, we applied the limiting current method (2). Here, I-V measurements were conducted at different total pressures (0.11MPa, 0.12MPa, 0.13MPa, 0.14MPa, 0.15MPa) for the cathode side. The flow rate of cathode gas (oxygen and nitrogen mixture) was 2000 sccm with different oxygen concentration (1%, 1.5%, 2%), and the flow rate of anode hydrogen was 100 sccm. The relative humidity of supplied gas was set 80% (80°C) in both sides.Table 1 shows measured parameters of CLs fabricated with three Pt carrying densities. The sample name represents the Pt carrying densities: CL20, CL30, CL50 used TEC10E20E, TEC10E30E, and TEC10E50E. The porosities measured by nitrogen adsorption method are similar as well as the pore size distributions (not shown here), and this means that the structures of the fabricated CLs are also similar. Using the porosity and the materials used for fabricating, the thickness of the CLs was estimated in Table 1. The thickness of the fabricated CLs becomes thicker with lower Pt carrying density carbon to set the Pt loading around 0.06 mg/cm2. Effective Pt surface area is calculated by multiplying the Pt loading and the electrochemical surface area (ECSA [m2/gPt]) estimated by CV measurements. The ECSA decreased as the Pt carrying density increased. This can be considered because the Pt particles aggregate on the carbon and the surface area becomes smaller. As a result, the effective Pt surface area of CLs fabricated with three Pt carrying densities are around 64 m2 pt/m2 CL for three CLs in Table 1.Figure 1 shows results of the I-V characteristics with the fabricated CLs at 1% and 2% oxygen concentration. The difference is pronounced with O2 2%: the voltage with CL30 is higher than those with CL50 and CL20 especially at higher current densities. With O2 1%, CL20 performance is the lowest even with the largest effective Pt surface area as shown in Table 1.To consider the contribution of the oxygen transport resistances to the performance differences, the oxygen transport resistance components were comparted in Figure 2. RO2 P,dep , RO2 P,ind are the pressure dependent and independent resistances respectively. The RO2 P,dep is considered to be the oxygen transport resistance in the GDL and the channel. The RO2 P,ind is considered to be the oxygen resistance in the CL, and the difference in the limiting current density in Figure 1 is caused by the RO2 P,ind with different CLs.The previous study by the authors (2) showed that the RO2 P,ind can be evaluated by dividing into three components: RO2 P,ind = RCL = RPt + Rdiss + Rpore . These are the oxygen transport resistance at the Pt surface, RPt , the dissolution resistance into ionomer, Rdiss , and the oxygen diffusion resistance in the CL pores, Rpore . From the simplified evaluation formula (2), the RPt is inversely proportional to the effective Pt surface area. Here, the Pt surface areas of the CLs are similar, as in Table 1. The Rpore is proportional to the CL thickness, and the thickest thickness of CL20 may contribute to the largest RO2 P,ind in Figure 2. However, the RO2 P,ind of CL50 is also larger than that of CL30 in spite of the thinnest thickness and the similar effective Pt surface area. These indicate that the dissolution resistance, Rdiss , could contribute to the RO2 P,ind for the CLs with the lower Pt loadings. The dissolution resistance, Rdiss , is inversely proportional to the CL thickness, and may contribute the larger RO2 P,ind of CL50. Therefore, it is necessary to consider the balance of these three components of the oxygen transport resistance. Figure 1

Experimental Evaluation of PEFC Catalyst Layer Structure to Reduce Oxygen Transport Resistances

To increase the output power of polymer electrolyte fuel cells (PEFCs), it is important to reduce the oxygen transport resistance in the cathode catalyst layer (CL). The authors have been conducted detailed analysis of the oxygen transport resistance elements: the diffusion resistances in the CL pores, the dissolution resistance into the ionomer, and the transport resistance at the Pt surface. This study improved the method of fabrication of CL and measurement of limiting current for reliable evaluation of oxygen transport resistance in the CL. Using the experimental results, the oxygen transport resistance elements were evaluated, and the transport resistance at Pt surface was confirmed to be dominant even in the improved methods. However, the difference between the model analysis and experimental values became large at CLs with low Pt loadings. To elucidate appropriate structures of the low Pt CLs with smaller oxygen transport resistance, further detailed study is needed.

A chainmail effect of ultrathin N-doped carbon shell on Ni2P nanorod arrays for efficient hydrogen evolution reaction catalysis

Exploring innovation strategies has huge potential to significantly improving both activity and stability of current catalysts. Here, a chainmail design is proposed to enable the electronic interaction of ultrathin nitrogen-doped carbon shell with Ni2P nanorod core arrayed on nickel foam (Ni2P@NC/NF) for simultaneously promoting the activity and stability in both alkaline and neutral hydrogen evolution reaction (HER). The easy penetration of valence electrons from active Ni2P core to NC shell enables the obvious improvement of HER performance compared to pure Ni2P. In 1 M KOH and 1 M PBS solution, the resultant Ni2P@NC/NF requires the ultralow overpotentials of only 93 and 96 mV to drive the current density of 10 mA cm−2 with the Faradaic efficiency of 96% and 94%, respectively. Remarkably, such a chainmail design also reveals an obviously improved stability with almost negligible performance degradation under the current density of 20 mA cm−2 for 30 h. Theoretical calculations confirm that the nitrogen-doped carbon shell improves the durability of transition metal phosphides by increasing the dissolution resistance of Ni atoms. The proposed concept may create a new pathway for synchronizing high activity and robust stability in manipulating heterogeneous catalytic properties.

Doped Ceria Nanoparticles with Reduced Solubility and Improved Peroxide Decomposition Activity for PEM Fuel Cells

Ceria nanoparticles (NPs) have unique catalytic properties which make them suited to scavenge degrading radical species and their precursor peroxides during PEM fuel cell operation. However, in the acidic environment of the fuel cell, ceria dissolves and the resulting cations migrate within the MEA, causing performance and durability losses. In this work, ex situ testing was used to evaluate the peroxide decomposition, selectivity towards radical generation, and solubility of Gd, Pr, and Zr-doped ceria NPs over a range of crystallite sizes and dopant levels. These doped materials exhibit better peroxide scavenging activity and dissolution resistance than undoped ceria. In these materials, activity is largely governed by increased surface area due to high internal porosity at smaller crystallite sizes compared to undoped ceria. Of the compounds tested, ceria NPs doped with 15 at% Zr (10 nm) and 5 at% Pr (17 nm) exhibited greater dissolution resistance than undoped ceria. Stabilization of the former doped NPs is attributed to crystallite agglomeration, while the increased stability of the latter is proposed to be due to its internally-porous, mesoscale structure suggested by its sorption isotherm. Both materials are more dissolution-resistant and active peroxide decomposers compared to undoped ceria but exhibit increased byproduct radical generation.

DFT-Based Calculation of Dissolution Activation Energy and Kinetics of Ni–Cr Alloys

A density functional theory investigation of the process of dissolution of Ni and Cr adatoms from model Ni–Cr(111) alloy surfaces is presented, both in vacuum and with explicit water molecules. The goal is to understand how the electronic structures solved using DFT can provide insights as to changes in valence, energy and coordination of the adatoms in the process of dissolving from the alloy surface. It is found that nearby Cr solute atoms increase the dissolution activation energy of Ni. Cr adatoms have a similar dissolution activation energy as Ni adatoms, except for one particular surface configuration that has a much smaller dissolution activation energy, which might promote selective dissolution of Cr in Ni–Cr alloys. To interpret the first-principles modeling results for the potential energy trajectory along the dissolution reaction coordinate, we provide a thermodynamic breakdown of the various terms that contribute to the dissolution activation and total reaction energy. The role of addition of Cr is explored on the dissolution kinetics of a Ni–Cr alloys of varying composition by constructing a model for the corrosion current density with DFT-based activation energies. Finally, dissolution resistance index is proposed as a quantifiable descriptor of the dissolution resistance of corrosion resistant alloys.

Selective Dissolution Resistance Control of EUV Photoresist Using Multiscale Simulation: Rational Design of Hybrid System

A photoresist (PR) that can be fabricated in sub-10 nm patterns with the introduction of extreme ultraviolet lithography (EUVL) is a key requirement for transistor downsizing. To produce such ultra...

Roles of Interstitial Nitrogen, Carbon, and Boron in Steel Corrosion: Generation of Oxyanions and Stabilization of Electronic Structure

The effects of N, C, and B interstitials on the corrosion resistance of Fe were investigated in chloride-free boric-borate solutions at pH 6.0 and 8.0. In potentiodynamic polarization at pH 8.0, the anodic dissolution resistance of Fe-0.3N and Fe-0.3C in the active and passive regions was higher than that of pure Fe. and are considered to be dissolved chemical species that contribute to the higher corrosion resistance of Fe-0.3N. Potentiodynamic polarization measurements in a solution with indicated that also decreases the anodic current densities in the active and passive regions, suggesting that the formation of contributes to the higher corrosion resistance of Fe-0.3C. First-principles calculations showed that the presence of N, C, and B in the Fe-lattice decreases the electronic density of states (DOS) at and near the Fermi level. The consistency between the active dissolution rates and the DOS at and near the Fermi levels of the specimens suggests that the more stable electronic structures occurred by the presence of N and C also result in the suppression of active dissolution of Fe. For Fe-0.3B and Fe-0.006B, the presence of iron boride precipitates promoted localized corrosion.

Electrochemical investigation of chalcopyrite (bio)leaching residues

Chalcopyrite is the most abundant but also the most recalcitrant copper sulfide mineral in leaching processes. The reasons for its refractory character are passivation and/or its semi-conductive properties. In our study chalcopyrite was hydrometallurgically processed via chemical leaching, electrochemical leaching, bioleaching and electrobioleaching in 2 l stirred tank laboratory experiments. Both biotic leaching treatments were more successful than both abiotic leaching experiments, however, overall the copper recovery was low due to the recalcitrant character of chalcopyrite. Various electrochemical techniques such as cyclic voltammetry, potentiodynamic polarization and electrochemical impedance spectroscopy were applied to investigate the differences in surface properties of the residues. Potentiodynamic polarization and cyclic voltammetric studies showed that any kind of leaching resulted in increased dissolution resistance and surficial redox inactivation compared to unprocessed chalcopyrite. However, if chalcopyrite was continuously in direct contact to the cathodic working electrode its surface was activated and showed even the highest oxidation currents which implicates increased leachability. Thus, at the surface of such chalcopyrite particles the mineral was converted into readier leachable minerals such as chalcocite. Additionally, electrochemical impedance spectroscopy (EIS) was carried out in the presence of ferrous and ferric iron. It turned out that surface activation via ferrous iron was not observed. In contrast, ferric iron led to successive passivation over time. The charge transfer resistance was the lowest for unprocessed and surface reduced chalcopyrite and the highest for chemically and electrochemically leached sulfide mineral. The findings of this comparative, electrochemical study support that passivation takes place to larger extend during abiotic leaching (chemical and electrochemical leaching) compared to biotic leaching (bioleaching and electrobioleaching).

AuPd/C core–shell and alloy nanoparticles with enhanced catalytic activity toward the electro-oxidation of ethanol in alkaline media

Carbon-supported Pd, Au@Pd core–shell and Au1–xPdx-alloyed nanoparticles were prepared by a chemical reduction method and characterized by different experimental techniques, including X-ray powder diffraction, transmission electron microscopy, scanning-transmission electron microscopy using bright-field and high-angle annular dark field detectors and X-ray energy dispersive spectroscopy. The catalytic mass activity toward ethanol oxidation was assessed by cyclic voltammetry and chronoamperometry at room temperature. The measurements showed that the addition of Au enhances remarkably the electrocatalytic activity of the material, due to the bifunctional effect of Au1–xPdx/C alloys, and the synergetic effect on Au@Pd/C, resulting in a dissolution resistance of core–shell catalysts at potentials of 1.5 V versus reversible hydrogen electrode. In situ Fourier transform infrared spectroscopy measurements showed that the mechanism for ethanol oxidation depends on the electrocatalyst structure and morphology. Acetate was identified as the main product of ethanol electro-oxidation on the studied electrocatalysts. However, the presence of a core–shell structure on Au@Pd/C resulted in enhanced ethanol oxidation selectivity toward CO2. The improvement of activity is attributed to the interaction between Pd shell and Au core.

Diagnosis of water failures in proton exchange membrane fuel cell with zero-phase ohmic resistance and fixed-low-frequency impedance

Water failures, which can be diagnosed with alternating-current impedance, is harmful to output properties and durability of the proton exchange membrane fuel cell. In this paper, an impedance-based measuring method of the zero-phase ohmic resistance is presented, which adjusts the measuring frequency to confine the impedance point within the ±3° sampling limitation area so as to guarantee the accuracy of 0.01 mΩ. The zero-phase ohmic resistance is sensitive to the membrane dehydration, and it decreases in the flooding process due to the gradual liquid water accumulation in the catalyst layer. The fluctuation of the zero-phase ohmic resistance increases in the flooding process, owing to the water state variation resulting from increasingly frequent water removal. A semi-empirical equivalent circuit model is used to analyze the change of mass transfer in the flooding process, and it is found that the diffusion resistance and the dissolution resistance of the reactant increase sharply. The fixed-low-frequency resistance is applicable in the flooding diagnosis, whose sensitivity changes with the chosen frequency. The highest sensitivity is corresponding to the peak value of the impedance magnitude. This paper provides adequate information about the water fault diagnosis, making sense to the fault-avoidance and the durability-promotion of the fuel cell.

Ab Initio Monte Carlo Simulations of the Acidic Dissolution of Stainless Steels Effect of Mechanical Deformation

This work is devoted to the Monte Carlo (MC) simulation of the acidic dissolution of mechanically deformed stainless steels (SS). Ab initio relaxation techniques are first used to calculate the bonding energies between atoms as a function of the interatomic distance. Dissolution kinetics of pre-deformed SS structures are then evaluated by means of an MC algorithm. Calculations show that the dissolution probability of surface atoms depends strongly on the strain field near the surface, compressed zones being found to dissolve more rapidly than extended ones. Mechanically induced defects, such as dislocation loops, were also investigated and shown to form preferential dissolution pathways due to the high levels of deformation and to significantly enhance the dissolution kinetics. Last, adding alloying elements is shown to increase the weakening effect of the strain field, regardless of the deformation mode. The addition of molybdenum for instance, known to improve the anodic dissolution resistance, may become less effective in deformed stainless steels.

Characterization and Corrosion Behavior of Functional Gradient Hydroxyapatite Coating

The aim of the present work is to examine the characterization and corrosion behavior of functional gradient hydroxyapatite coating deposited on titanium-based alloy by plasma spray coating process. The functionally graded coating is designed to provide the crystalline hydroxyapatite at the interface with metallic substrate and the amorphous hydroxyapatite at the outer surface. It is considered that the top amorphous layer of hydroxyapatite has higher bioactivity, and its initial dissolution will lead to bone tissue growth enhancement and bonding, whereas the underneath crystalline hydroxyapatite coating after heat treatment is expected to enhance the long-term stability of coating at the interface with metal. The heat treatment of the underneath as-sprayed coating for crystallization was performed at 700 °C for 1 h. The characterization of the coatings was performed by various techniques such as scanning electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction analysis, surface roughness, and microhardness. It was observed from potentiodynamic scan that heat-treated coating exhibited better dissolution resistance as compared to the as-sprayed coating. Heat treatment of the hydroxyapatite coating resulted in improved crystallinity of the coating which may provide long-term stability to the coating.

Piperine as a Placebo: Stability of Gelatin Capsules without a Cross-Linker

Gelatin has been the biomaterial of choice for decades now. Its low cost, renewable, nontoxic, and biodegradable properties make it one of the most desirable materials for controlled release applications. However, the usage of gelatin is limited by its poor mechanical/thermal stability and high water solubility. Chemical cross-linkers and hydrophobic modifications of gelatin have solved this problem, but they lead to the problem of toxicity and/or a high processing cost. This research attempts to employ a nontoxic hydrophobic drug molecule to curb early degradation of gelatin in an aqueous environment. We report the design of non-cross-linked gelatin capsules with a high dissolution resistance in an aqueous medium. Piperine, a hydrophobic drug (solubility = 40 mg/L in water), was coated on the gelatin capsules to enhance its stability in an aqueous environment. The hydrophobic piperine molecules repelled the water molecules to intensify its dissolution resistance. This stabilization was used to control the release of naproxen sodium, encapsulated inside the gelatin matrix. Piperine, in this case, acts as a placebo; i.e., it has zero therapeutic effect, but its presence was necessary to control the early degradation of the gelatin matrix. The deposition of piperine was done using the solvent evaporation method where ethanol was used as the solvent. The wettability studies revealed the hydrophobic nature of the surface after the deposition of piperine, while SEM analysis showed the presence of long cylindrical (fiber-like) structures over the gelatin surface. Further investigation (FTIR/ATR and molecular dynamics) revealed that the long fiber structures were due to the crystallization of piperine over the surface of gelatin. This crystallization was triggered by the intermolecular association (hydrogen bond) of ethanol and piperine. These observations enabled us to optimize the piperine loading protocol over the gelatin capsules that helped in achieving a zero-order naproxen release for 32 h.

Fabrication and Characterization of Suspension Plasma-Sprayed Fluoridated Hydroxyapatite Coatings for Biomedical Applications

Fluoridated hydroxyapatite (FHA) coatings were prepared on a Ti substrate using a suspension plasma spraying technique. The crystalline phases and chemical compositions of the coatings were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. The analysis confirmed that the coating consisted of an FHA phase. The corrosion behavior in simulated body fluid was studied using potentiodynamic polarization tests, and the results indicated that the FHA coating greatly enhanced the corrosion resistance of the Ti substrate. The chemical stability of the FHA coatings was assessed by evaluating the release of Ca2+ ions. The results indicated that the substitution of fluorine into the hydroxyapatite (HA) structure had a positive effect on the dissolution resistance of the HA. The antibacterial activity was investigated using a surface-plating method; the results revealed that the antibacterial activity of the FHA coating was greater than that of the pure HA coatings. During cell culture tests, the FHA coating did not exhibit cytotoxicity toward the osteoblast cell line, and the cell proliferation was comparable with that of the HA coatings. The antibacterial activity and cell culture results suggested that the plasma-sprayed FHA coating possesses good antibacterial qualities, but is biocompatible with osteoblasts. The promising features of the FHA coating render it suitable for orthopedic and dental applications.

Model for the Correlation between Anodic Dissolution Resistance and Crystallographic Texture in Pipeline Steels.

This paper presents a novel physical–mathematical model to describe the relationship between the crystallographic texture and corrosion behavior of American petroleum institute (API) 5L steels. Symmetric spherical harmonic functions were used to estimate the material’s corrosion resistance from crystallographic texture measurements. The predictions of the average corrosion resistance index made from the crystallographic texture were in good agreement with those obtained from potentiodynamic polarization and electrochemical impedance spectroscopy measurements for the studied steels. This agreement validates the capacity of this model and opens the possibility of applying it as a novel criterion for materials selection and design stages to combat corrosion problems.

Nanoscale simulation of local gas transport in catalyst layers of proton exchange membrane fuel cells

Reducing Platinum amount in proton exchange membrane fuel cell (PEMFC) is one of the main tasks to achieve low cost PEMFC. Recently, significant performance loss has been found under low Pt loading due to local mass transport limitations. In this study, pore-scale simulations are conducted to study oxygen transport within four-constituent microscopic structures of catalyst layer including a carbon particle, ionomer, Pt particles, and primary pores inside the carbon particle. Multiphase physicochemical processes are considered, including oxygen dissolution at the pore/ionomer interface, oxygen diffusion within the ionomer film and inside the primary pores, and reactions at the Pt interface. Local transport resistance is calculated based on the pore-scale concentration field predicted. The simulation results are compared with existing experimental results and 1D models. Simulation results show that dissolution resistance at the secondary pore/ionomer interface is about 10–50 times higher than that inside the ionomoer. Local transport resistance increases as Pt loading decreases, especially under Pt loading of 0.1 mg cm−2. Besides, local transport resistance can be reduced by depositing more Pt outside the carbon particle, alleviating agglomeration and/or decreasing the ionomer thickness. The simulation results indicate that local transport characteristics should be considered when developing 1D agglomeration model of catalyst layer.

Analysis of Oxygen Transport Resistances in the Catalyst Layers with Different Carbon Supports in PEFC

In polymer electrolyte fuel cells (PEFCs), the catalyst layer (CL) of the cathode needs a large amount of Pt because of the slow oxygen reduction reaction. Since electron, proton, and oxygen are necessary for the cathode reaction, achieving the optimum structure of electrode CL and the efficient transport of the reactants is significantly effective to reduce the usage of Pt catalyst. In this study, the effects of carbon structure on oxygen transport were evaluated using CLs fabricated under several conditions. We compared the performances using fabricated CLs with Ketjen black and Vulcan. Furthermore, the oxygen transport resistance in the CLs was evaluated. Pore size distribution (PSD) of the CL was measured by nitrogen physisorption method, and the CL structural parameters were estimated using the estimation model (1). Using the limiting current density method, we evaluate various oxygen transport resistances in the CL and discuss the contributions of these resistances to the cell performance. Figure 1 shows the estimated schematics of Pt-supported Ketjen black and Vulcan with ionomer. To investigate the structure of the fabricated CLs, we measured the PSDs by nitrogen physisorption method, and the results are shown in Figure 2. In the case of using Ketjen black, there is a small peak around 3-4 nm pore diameter, whereas in the case of Vulcan this peak does not exist. The small peak is considered to correspond to the pores in the carbon particles with a diameter of ~ 10 nm, and the difference in the PSDs for the self-produced CL is caused by the characteristics of the Vulcan with few pores in the particle. From these results, it is expected that most of the platinum particles are located on the outer surface of the Vulcan, and oxygen can easily diffuse to the platinum particles through the ionomer. Figure 3 shows the characteristics of the oxygen transport resistance of different thick CLs. By multiplying the measured oxygen transport resistance in the CL by the thickness of the CL, it is possible to evaluate only the change in the diffusion resistance in the CL pores, eliminating the influence of the oxygen transport resistance on the platinum surface and the dissolution resistance into the ionomer (1). From the gradients of the lines in Fig. 3, the effective diffusion coefficients can be estimated: DCL,eff O2=7.2×10-7 [m2/s] for the CL with Ketjen black and DO2 CL,eff =4.3×10-7 [m2/s] for that with Vulcan. The smaller effective diffusion coefficient with Vulcan is caused by the lower porosity. Figure 4 shows the characteristics of the oxygen transport resistance of the CLs having different platinum surface areas. The vertical axis represents the oxygen transport resistance in the CL, and the horizontal axis represents the inverse of the platinum surface area. Here, Pt-supported carbons with three different Pt densities were used, and the carbon amounts were set similar. Based on the gradients of the lines, the value of the oxygen transfer rate constant kPt at the platinum surface are estimated to be kPt=3.7×10-3 [m/s] for the CL with Ketjen black and kPt=9.3×10-3 [m/s] for that with Vulcan. Figures 5 and 6 show the results calculating the oxygen transport resistance of the fabricated CLs using the parameters estimated from the experiment. The oxygen dissolution rate kdiss=7.0×10-3 [m/s], estimated in the previous study (1), was applied here. With the CL with Ketjen black, the resistance at the platinum surface, R Pt , is a dominant factor, whereas the contribution of the resistance at the platinum surface with Vulcan reduces. This is considered to be because platinum particles are arranged outside the carbon particles. However, the diffusion resistance in the pores with Vulcan increases due to the lower porosity. This suggest that it is effectiveto increase the porosity for further reduction in the oxygen transport resistance in the thick CL with Vulcan. Reference Tabe, et al., ECS Trans., 80(8), 205 (2017). Figure 1