In order to improve the performance and durability of polymer electrolyte fuel cells (PEFCs), various improvements in the microstructures of cathode catalyst layers (CLs) were initiated in the early ...1990s. More recent advances in CL materials are highlighted, including carbon supports for improved accessibility of Pt nanoparticles (NPs), adsorption of ionomer on the Pt surface, high-oxygen-permeability ionomers, corrosion resistance of mesoporous and microporous carbons, and conductive ceramic supports with a fused-aggregate network structure. These approaches are summarized as stepwise improvements. The influences of the support structure on the distribution of Pt NPs and ionomer are reviewed, as well as their effects on performance and durability. These approaches for carbon supports are extended to conductive ceramic supports and the unique advantages are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The pursuit of realism in the ERS environment is progressing with ICT development. On the other hand, there is no discussion focused on reproducibility that includes comprehensive load side ...characteristics, such as propeller characteristics through the shaft system and hull resistance characteristics, which is one of important knowledge requirements specified in IMO Model Course 2.07. In this report, the author focuses on load side characteristics in ERS performance in order to make clear typical challenges facing ERS, advance marine engineer training and promote research and development related to ship engine operation management, all of which are rarely considered in the current general ERS. In this report, the author introduces the results of an experiment based on actual ship measurements and numerical simulations regarding the reproducibility of the power load characteristics while promoting greater awareness of the issue raised in this paper. The author hopes for wider use and development of ERS that considers the importance of power load characteristics and more robust discussions on improving the ERS environment.
We investigate the effects of the carbon supports on the Pt distribution, ionomer coverage and cathode performance of carbon-supported Pt catalysts, by using STEM observation, N2 adsorption analysis ...and electrochemical characterization. According to the STEM observation, the effective Pt surface area (S(e)Pt), which is determined by the location and size of the Pt particles on the supports, increases in the following order: c-Pt/CB < c-Pt/GCB < n-Pt/AB800 < n-Pt/AB250. The N2 adsorption analyses show that the Pt particles observed in the interior of the CB and AB800-supported Pt catalysts during the STEM observation could be ascribed to the hollow structures inside the carbon supports, which decrease their effective Pt surface areas. The S(e)Pt values are in good agreement with the cell performance in the high current density region. In spite of the highest Pt utilization (UPt) value (>90%) and uniform ionomer coverage, the c-Pt/CB catalyst shows the lowest cell performance due to the lower S(e)Pt value. On the other hand, the n-Pt/AB250 catalyst, for which all of the Pt particles exist only on the exterior surface, is found to be the most attractive in order to generate the large current densities required by actual fuel cell operation.
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•Effective Pt surface area was in the order: Pt/CB < Pt/GCB < Pt/AB800 < Pt/AB250.•Hollow structure of the CB and AB800 decreased the effective Pt surface area (S(e)Pt).•S(e)Pt values were in good agreement with the performance at high current densities.•This is due to improvement of the effective Pt surface area and ionomer distribution.•The AB-supported Pt catalysts had well-balanced supply paths for protons and oxygen.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Polyamide (PA) is a semi-crystalline polymer in which the main chain is configured by the repeating units of amide bonds (-NHCO-). The strength of PA is achieved by intermolecular hydrogen bonding ...between the hydrogen and oxygen atoms of the amide bonds. In this study, the effects of the density of the amide group and crystallinity were evaluated by uniaxial tensile tests of commercial PA11, PA610, PA6, and PA-MXD10. The maximum stress was proportional to the tensile rate, and the stress-strain curves of the PAs with small crystallinity showed a sharp drop after the maximum stress. In contrast, a gradual change in the stress was observed around the maximum stress of the PAs with high crystallinity. Subsequently, a time-dependent nonlinear mechanical model based on the unfixed molecular chain network (MCN) model is proposed to predict the mechanical behavior of PAs. Because this model was proposed for amorphous epoxies, we modified the unfixed MCN model to reproduce the mechanical response of semi-crystalline PAs. In this study, a constant resistance to debonding in the original unfixed MCN model was replaced by the function of the viscoplastic strain. The modified version of the unfixed MCN model reproduced the gradual softening at a large strain range and the effects of the crystallinity on the mechanical response of the PA.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A nonlinear elastic-inelastic model for a thermosetting polymer is proposed based on the molecular chain network theory. In the proposed model, the bond of the polymer chain is divided into physical ...and chemical bonds, and the physical bond is allowed to separate and recombine during the deformation. The decrease in the rigidity and increase in the inelastic strain are related to the development of the physical bond density to represent the characteristic deformation behavior of the polymer. A rate-form large deformation constitutive equation is then formulated based on the updated Lagrangian method. Additionally, deformation behaviors of the epoxy under monotonic and cyclic tensile tests were evaluated by experimental and computational studies. The experimental results of the monotonic tensile test displayed a gradual transition from elastic to inelastic deformation, strain softening behavior after the macroscopic yielding stress, and an increase in the initial slope and the macroscopic yielding stresses with an increasing strain rate. The computational model can represent such characteristics by controlling the development of the physical bond density. In a cyclic test, a decrease in the rigidity and an increase in the residual strain with increasing cycles were observed even in a small strain range. Such inelastic deformation depended on the strain rate and the given upper stress in the cyclic test. Further, the proposed model successfully reproduced such nonlinear behavior in the cyclic test.
The bond of the polymer chain is divided into physical and chemical bonds, and the decrease in the rigidity and increase in the inelastic strain are related to the development of the physical bond density to represent the characteristic deformation behavior of the polymer. Display omitted
•A nonlinear elastic-inelastic model for a thermosetting polymer is proposed based on the molecular chain network theory, in which the development of the physical bonding is introduced.•Deformation behaviors of the epoxy under monotonic and cyclic tensile tests were evaluated by experimental and computational studies.•The proposed model successfully reproduced time-depended nonlinear behavior in the monotonic and cyclic tests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Engineering materials usually exhibit heterogeneity such as that observed in the polycrystalline structure of metals, and this heterogeneity affects the nonuniform deformation of a material. In this ...study, the micro- to macroscopic nonuniform deformation of polycrystalline copper specimen with a curved gage section is evaluated by a finite element method (FEM) simulation based on the second-order homogenization method (2nd-HM). The effects of the microstructure size and macroscopic stress gradient on the nonuniform deformation of the material are then investigated by comparing the simulation and experimental results. A two-dimensional plane strain polycrystalline microstructure was periodically applied to all the integration points in the macrostructure; the anisotropic deformation of the crystal grains is represented by the conventional crystalline plasticity constitutive equation. The computational results indicate that the interaction between nonuniform deformation on the micro and macroscopic scales induces a slight size effect in the material. However, the FEM simulation based on the 2nd-HM could not predict the decrease in the macroscopic strain concentration in the specimens with large crystalline grains, which was observed in the experimental studies, because of random strain localization resulting from the microscopic heterogeneity.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We investigated the effects of short-side-chain (SSC) perfluorosulfonic acid ionomers on the electrochemical properties, fuel cell performance and ionomer distribution of a highly dispersed Pt/GCB ...catalyst with a low Pt loading, 0.05 mg cm−2. The SSC ionomers in the cathode catalyst layers (CLs) resulted in an improvement of the Pt utilization (UPt) and Pt effectiveness (EfPt) values compared with those for the conventional long-side-chain (LSC) ionomer. Furthermore, the SSC ionomers with high ion exchange capacity (IEC), e.g., SSC-1.43 and SSC-1.80 ionomers, exhibited significantly enhanced cell performance under low to medium relative humidity (RH) conditions. This result is ascribed to the higher proton conductivity of the SSC ionomers and more effective trapping of water that is produced during the oxygen reduction reaction (ORR) than those of the LSC ionomer. It was also found that the SSC ionomers showed better continuity and uniformity on the Pt and carbon particles than the LSC ionomer, which might have led to improvement of both the mass transport and the proton-conducting network in the CLs. The application of the SSC ionomers as binders demonstrated an increase of the performance at the low Pt loading fuel cell cathode over a wide range of humidity.
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•Pt utilization and effectiveness improve in cathodes with short side chain ionomers.•Short side chain (SSC) ionomer-based cathodes perform better at low humidity.•This is due to higher proton conductivity because of more effective water trapping.•The SSC ionomer covered the Pt and GCB particles more uniformly and continuously.•This leads to improvement of mass transport and proton-conducting networks.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Oxygen transport is a serious limiting factor on the performance of polymer electrolyte fuel cells (PEFCs). In the present study, without modification of either the chemical structure of the ionomer ...or the Pt surface, the oxygen transport resistance in ionomer films (R CL,film) was successfully mitigated via a newly developed electrospray (ES) catalyst layer (CL) preparation. We prepared the CL according to two different ionization modes positive ionization mode (ESP) and negative ionization mode (ESN) and ionomer/carbon mass ratios (I/C) of 0.3 and 0.7. The ionomer morphology revealed differences according to the ionization mode, as analyzed by scanning transmission electron microscopy. Spherical and dendritic ionomer morphologies were observed resulting from ESP and ESN, respectively. To quantitatively estimate R CL,film values, limiting current measurements were used. Consequently, the CL prepared by ESN exhibited the lowest R CL,film value compared to that for the conventional pulse-swirl-spray (PSS) method and ESP (I/C 0.3 PSS, 61; ESP, 94; ESN, 40 s m–1; and I/C 0.7 PSS, 68; ESP, 66; ESN, 46 s m–1). Moreover, the difference in the ionomer morphology not only influenced the mass activity at low current density but also helped to implement superior performance at high current density. Therefore, it was confirmed that the decreased thickness of the ionomer film covering the surface of the catalyst with ESN decreased R CL,film by a factor of 1.5 and, as a result, improved the overall PEFC performance by the same factor.
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IJS, KILJ, NUK, PNG, UL, UM
•The interaction between the microstructure-induced and the specimen shape-induced non-uniform deformation was evaluated from experimental and numerical studies of the uniaxial tensile tests of the ...polycrystalline copper specimen with a curved gauge section.•The deformation bands, in which the width and length are characterized by grain size, develop during the uniaxial tensile test of the polycrystalline specimen.•We proposed a constitutive equation for the plastic strain as a function of the local stress and finite volume averaged stress.
In polycrystalline materials, with the increase in grain size relative to the macrostructure, the collective behavior of crystal grains affects their macroscopic deformation field. To investigate the effect of relative size on the mechanical behavior of polycrystalline materials, the interaction between the microstructure-induced non-uniform deformation and the specimen shape-induced non-uniform deformation was evaluated based on experimental and numerical studies of uniaxial tensile tests of polycrystalline copper specimens with a curved gauge section. The effects of the macroscopic stress gradient and grain size on the strain field of the specimen were evaluated using specimens with different curvature radii obtained from different thermal treatment conditions. The development of strain distribution was measured using the digital image correlation method. A high strain concentration was observed at the minimum cross-section region in the specimen with smaller grains, whereas such strain concentration was relaxed in the specimen with larger grains because a random strain distribution occurred owing to the polycrystalline structure. A full-scale crystalline plasticity finite element method simulation, under conditions similar to those in the experiment, was then performed. Deformation concentrated zone, in which the length and width depended on the grain size, occurred in the polycrystalline specimen. The cross-section of the specimen was locally reduced when the deformation concentrated zone reached the free surface, and the tensile force became smaller for the specimen with larger grains. To discuss the relative specimen size effect, the plastic strain was divided into local and nonlocal plastic strains. Both the experimental and simulation results clarified that the nonlocal plastic strain gradient evaluated in the finite volume region increased with the region-averaged stress. From these results, we proposed a constitutive equation for the plastic strain as a function of local stress and finite volume averaged stress. The nonlocal plastic work for the evaluation region, which is estimated using the nonlocal strain gradient, increased with the stress during the strain-hardening stage in both the simulation and experimental results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For the large-scale commercialization of polymer electrolyte fuel cells (PEFCs), it is very important to reduce the amount of Pt by developing highly efficient cathode catalyst layers (CLs) due to ...the high cost and limited availability of Pt resources. We investigate the effects of high oxygen permeability ionomers and ion exchange capacity (IEC) on the cathode performance and durability of PEFCs. The high oxygen permeability ionomers are expected to increase the flux of oxygen near the Pt surface of the three-phase boundary, which is critical in the case of extremely low Pt loadings. The low Pt loading cathode CLs are prepared from the AB250-supported Pt catalyst. From the current-voltage (I-E) curve measurements, the high oxygen permeability ionomers improve the cathode performance without any adverse effects. During durability testing, the high IEC ionomers lead to increased solubility of Pt and cause severe Pt agglomeration and a large amount of redeposition of Pt particles in the membrane. Based on these results, we propose a strategy of ionomer property selection to improve both cell performance and durability.
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