In this study, we focused on nano- and micro-scale cracks in the catalyst layer and the micro porous layer of polymer electrolyte membrane fuel cells (PEMFCs) and its impact on cell performance. We applied wet-dry cycles to a conventional test cell to investigate crack generation in the catalyst layer and the micro porous layer. Wet-dry cycles, in which cell temperature was kept at 353K with high- and low-humidified gas alternately applied to the cell, potentially induced mechanical stress to a membrane electrode assembly (MEA) due to membrane hydration and dehydration. As a result, significant degradation of performance was found after the wet-dry cycles. We performed cross-sectional analysis of MEA by using a cross-sectional polisher (CP) and scanning electron microscopy (SEM) to investigate nano- and micro-scale crack generated by the wet-dry cycles in the MEA. The SEM images showed that nano- and micro-scale cracks were significantly generated in the catalyst layer as well as in the micro porous layer after the cycles. We identified cracks in the MEA with different morphologies according to the SEM images, hence, through-plane cracks and in-plane cracks. Through-plane cracks have a deep-valley structure in the MEA while in-plane cracks are formed in an interfacial region between the catalyst layer and the micro porous layer. In-plane cracks could be generated by detachment of the catalyst layer from the micro porous layer due to the wet-dry cycles and potentially decrease in cell performance due to deterioration of electron transport in the MEA. In addition, in case liquid water is accumulated in in-plane cracks, these cracks potentially disturb gas diffusion from the micro porous layer to the catalyst layer. These results clearly showed that mechanical stress induced crack generation in the MEA, resulting in intensive effects on cell performance in PEMFC.

Gas diffusion layer (GDL) is undoubtedly one of the most complicated components used in a polymer electrolyte fuel cell (PEFC) in terms of liquid and gas transport phenomena. An appropriate fuel cell design seeks a fundamental study of this tortuous porous component. Currently, porosity and gas permeability have been known as some of the key parameters affecting liquid and gas transport through GDL. Although these are dominant parameters defining mass transport through porous layers, there are still many other factors affecting transport phenomena as well as overall cell performance. In this work, microstructural properties of Toray carbon papers with different thicknesses and for polytetrafluoroethylene (PTFE) treated and untreated cases have been studied based on scanning electron microscopy (SEM) image analysis. Water droplet contact angle as a dominant macroscale property as well as mean pore diameter, pore diameter distribution, and pore roundness distribution as important microscale properties have been studied. It was observed that the mean pore diameter of Toray carbon paper does not change with its thickness and PTFE content. Mean pore diameter for Toray carbon papers was calculated to be around 26 μ m regardless of their thicknesses and PTFE content. It was also observed that droplet contact angle on GDL surface does not vary with GDL thickness. The average contact angle for 10 wt.% PTFE treated GDLs of different thicknesses was measured about 150°. Finally, the heterogeneous in-plane PTFE distribution on the GDL surface was observed to have no effect on mean pore diameter of GDLs.

MnCo 2 O 4 spinel coatings are designed to be used on metallic interconnectors in SOFC devises to decrease oxidation rate of the metallic interconnect and to prevent the evaporation of harmful CrO 3 and Cr 2 (OH) 2 compounds. These Cr-compounds degrade the long-term performance of the SOFC by migrating to the triple phase barrier (TPB) of the cathode and reduce back to Cr 2 O 3 . MnCo 2 O 4 spinel coatings, used in this study, were manufactured by using a novel solution precursor plasma spray (SPPS) process and heat treated in oxidizing environment. Deionized water based solutions of Mn(NO 3 ) 2 •4H 2 O and Co(NO 3 ) 2 •6H 2 O were used as a feedstock material. Concentration of the metal cations in the solutions was adjusted to 3 M. Ferritic stainless grade Crofer 22 APU with the thickness of 0.5 mm and surface roughness of R a < 0.5 μm was used as a substrate material. The coatings were manufactured using a Sulzer Metco A3000S plasma spray system with F4-MB plasma gun with modified solution feeding hardware. Coatings with different microstructures were sprayed using different spraying parameters, e.g. the type of plasma gases used. The as-sprayed coatings were aged at 700 °C for 500 h in oxidizing environment, in order to study the stability of the coating, the growth of the Cr-scale and the Cr-transport through the spinel coatings. The microstructural characterization for the as-sprayed and the oxidized coatings were done using a field-emission scanning electron microscopy (FESEM) with SE-mode. The quantitative analyses were executed with energy dispersive spectroscopy (EDS), and in addition X-ray diffraction (XRD) was used for qualitative studies. The coatings with various microstructures were sprayed. The densest microstructure was sprayed using Ar-He plasma gas. Also the crystallographic equivalence for MnCo 2 O 4 was achieved when Ar-He plasma was used with 40 mm spraying distance. Ageing caused the increase in structural porosity. On the interface between the coating and the interconnect, a dense spinel layer was formed which effectively prevented the Cr-transport forming approximately 500 nm thick Cr-rich sub-scale.

The ultimate goal of cold start of hydrogen-powered polymer electrolyte fuel cell vehicles is to minimize the significant system thaw energy requirement and to achieve the short time period desired for freeze start (e.g. less than 30 seconds) in a subfreezing environment. As part of an effort to improve cold start capability for fuel cell vehicles, this work presents a new thaw-at-start strategy using electrical characteristics of vanadium oxide thin films as self-heating source at sub-zero temperature. Vanadium-based thin film coated on the surface of flat bipolar plates (e.g. carbon-based graphite and metallic bipolar plates) have been synthesized by a dip-coating method via aqueous sol-gel chemistry. Subsequently, the detailed in-/ex-situ analyses of the thin films have been carried out using diverse diagnostic techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition, crystallinity, and microstructure. In addition, electrical switching characteristics of the thin films on bipolar plates was cautiously observed over a temperature range from −20°C to 80°C by means of 4-point probes installed in a thermo -hygrostat. By doing so, it has been possible to correctly infer the relationship between a tendency of the thermally-induced electrical switching hysteresis and bipolar plate materials. Also, comprehensive theoretical study on the basis of the experimental results have been performed to estimate the heat dissipation rate by Joule heating from the solid thin films on bipolar plates for the rapid cold-start operation of fuel cell vehicles.

The present work investigated a new method of calculating effective transport properties of solid oxide fuel cell (SOFC) electrodes from three-dimensional (3D) physically realistic network structures. These physically realistic network structures are topological equivalent representations of reconstructed microstructures in the form of spheres (nodes or bodies) and cylinders (segments or throats). Maximal ball algorithm is used to extract these physically realistic network structures from the series of two-dimensional (2D) cross-sectional images of SOFC electrodes. Dual-beam focused ion beam - scanning electron microscopy (FIB-SEM) is performed on SOFC electrodes to acquire series of 2D cross-sectional images. Finite element method is implemented to compute the effective transport properties from the network structures. As an example, we applied this method to calculate the effective gas diffusivity of lanthanum strontium manganite (LSM) of SOFC. The results obtained from physically realistic network structures are compared with reconstructed 3D microstructures.

Automated manufacturing techniques are needed to reduce production costs for polymer electrolyte membrane (PEM) fuel cell electrodes. The work presented in this paper focuses on the use of a low pressure, low volume direct spray valve that uses air pressure to atomize fluids and transfer them to a gas diffusion layer (GDL) to produce a gas diffusion electrode (GDE). Two of these electrodes would then be joined with a polymer electrolyte membrane to produce a fuel cell membrane electrode assembly (MEA). Accurate and reproducible deposition methods such as this will result in less wasted materials, especially platinum, and increased throughput compared to common laboratory-scale techniques such as paint brushing and Mayer-rod coating. In this study, the production of inks will be discussed including a catalyst ink containing platinum nano-particles supported on carbon (20% loading by weight) and a similar analog ink which is identical except for that it does not contain the platinum. Two different substrates, mylar transparency film and actual carbon paper GDL substrate will be used and presented in this study. Ink rheology (viscosity, solids content, etc.) will also be discussed as it pertains to optimizing spray pattern uniformity and process efficiency. Initial results of thickness measurements which are used for determining uniformity and the required overlapping of multiple coats will be presented. In addition, a comparison of scanning electron microscopy (SEM) images of electrode surface structures prepared by mayer-rod and spraying will be shown. A brief discussion of the future work planned by the authors in order to study the effects of processing variables on actual fuel cell performance will also be given.

An investigation of the liquid water saturation across the cross-section of an operating polymer electrolyte fuel cell is performed to analyze the saturation discontinuity predicted by numerical models. Numerical models have predicted a discontinuity in the liquid water saturation at the interface of the micro-porous layer and the coarser macroporous region of the gas diffusion layer. High-resolution through plane neutron radiography is used to acquire the water content distribution across the thickness of the gas-diffusion layer and study the effects of the interface. The measured liquid water profiles indicate no obvious discontinuity in the liquid water saturation across the cross-section of the bi-layer gas diffusion layer when large areas are averaged spatially. Evidence of the discontinuity is found when small spatial averaging is used in certain locations. Other locations show no evidence of the discontinuity. Scanning electron microscopy is used to examine the microstructure of two types of the bi-layer diffusion media. The images show that the approximation of the interface as a sudden, distinct feature may not be appropriate. The results suggest that a model that considers the existence of an interfacial region in the diffusion media may be appropriate, in which the properties vary continuously.

The high temperature mechanical properties in a glass-ceramic sealant of BaO-B 2 O 3 -Al 2 O 3 -SiO 2 system was studied by four-point bending test at room temperature, 550°C, 600°C, 650°C, and 700°C, to investigate the variation of Young’s modulus, flexural strength, and stress relaxation. Weibull statistic analysis was applied to describe the fracture strength of the given glass ceramic. The crystalline phase was produced by controlled heat treatment and analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the flexural strength was enhanced at high temperatures when the testing temperature was below the glass transition temperature (T g ). This was presumably due to a crack healing effect taking place at high temperature. Significant stress relaxation for the given glass ceramic was observed to generate extremely large deformation without breaking the specimens when the testing temperature was set at 700°C.

Fabrication of defect free co-sintered electrolytes with thickness between 12 μm and 40μm has been demonstrated on planar and tubular cells produced via a spray coating process. Leak testing using a helium leak method showed low diffusional leak rates for cells using optimized spray parameters. The electrolytes were characterized using scanning electron microscopy to qualitatively assess pin holes. Average open circuit voltages (OCVs) of 1080 mV were obtained on tubular cells with spray-coated electrolytes using 3% humidified hydrogen as the fuel. This paper presents spray coating as a viable, cost effective method for electrolyte application in co-fired, anode supported SOFCs.

This study experimentally examines the effect of nitrogen doping on the activity of Pt/C catalyst systems. The investigation was accomplished through the development of geometrically well-defined model catalytic systems consisting of tunable assemblies of Pt catalyst nanoparticles deposited onto both N-doped and undoped highly-oriented pyrolytic graphite (HOPG) substrates. N-doping was achieved via ion beam implantation, and Pt was electrodeposited from solutions of H 2 PtCl 6 in aqueous HClO 4 . Morphology from scanning electron microscopy (SEM) and catalytic activity measurement from aqueous electrochemical analysis were utilized to examine the N-doping effects. The results strongly support the theory that doping nitrogen into a graphite support significantly affects both the morphology and behavior of the overlying Pt nanoparticles. In particular, nitrogen-doping was observed to cause a significant decrease in the average Pt nanoparticle size, an increase in the Pt nanoparticle dispersion, and a significant increase in catalytic activity for both methanol oxidation and oxygen reduction.

Fuel cells are a promising technology to deal with energy sustainability, especially for mobility purposes the Proton Exchange Membrane Fuel Cell and hydrogen produced from biomass could be coupled to overcome the amount of CO 2 emissions. In order to improve fuel cells performances the search for new electrocatalysts has a great importance in this technology the challenge for a fuel cell catalyst that is less poisoned by CO is one of the most important field in low temperature fuel cell developments that use alcohol and hydrocarbons as primary fuels. In this work PtSm, PtTb, PtDy, PtU, PtRuMo and PtRuDy systems have been synthesized by the colloid method, investigated by the following techniques: X-rays fluorescence analysis (XFA), X-rays powder diffraction (XRD), X-rays photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), cyclic voltammetry (CV) and polarization curves (Exi). The results obtained in this work shows that PtRuMo is the best choice for direct methanol oxidation. For direct ethanol oxidation the higher activity was found in PtRuDy system. PtU system was investigated and showed an interesting behaviour in ethanol oxidation. After two cycles of H 2 /O 2 and ethanol/O 2 the catalyst was able to reach the initial figures on hydrogen/oxygen oxidation which means that no degradation of the catalyst was indentified.

Considerable interest exists in the application of single wall carbon nanotubes (SWNTs) to proton exchange membrane fuel cells (PEMFCs). Proposed applications include use as anode materials in both hydrogen and direct methanol fuel cells, solid polymer electrolyte additives, active cathode materials, and bipolar plate interconnects. SWNTs have extremely high electrical conductivity and catalytic surface areas which make them potentially outstanding active materials for PEMFC electrodes. Additionally the enhanced mechanical properties may play a roll in developing new fuel cell designs such as thin-film microelectronic fuel cells. In a previous study SWNTs were combined with commercially obtained E-TEK Vulcan XC-72 and Nafion® to produce composite cathode membranes. The addition of nanotubes resulted in enhanced fuel cell performance over an equivalent weight percent doping of E-TEK alone. This increased performance was achieved with a 50% reduction in the quantity of platinum present in the cathode. In the present study we investigate fuel cell performance when both the anode and cathode membranes contain graphite, platinum and SWNTs. The SWNTs were characterized by use of thermogravimetric analysis, Raman and UV/VIS/NIR spectroscopes as well as high resolution field emission scanning electron microscopy. Fuel cell performance was determined by comparison of the IV characteristics.

The production of hydrogen was investigated in a fixed bed tubular reactor via steam reforming of methanol using CuO/ZnO/Al 2 O 3 catalysts prepared by wet impregnation method and characterized by measuring surface area, pore volume, X-ray diffraction pattern and scanning electron microscopy photographs. The SRM was carried out at atmospheric pressure, temperature 493–573 K, steam to methanol molar ratio 1–1.8 and W/F 3 to 15. Effects of reaction temperature, contact-time, steam to methanol molar ratio and zinc content of catalyst on methanol conversion, selectivity and product yields were evaluated. The addition of zinc enhances the methanol conversion and hydrogen production. The excess steam promotes the methanol conversion and suppresses the carbon monoxide formation. Different strategies have been mentioned to minimize the carbon monoxide formation for the steam reforming of methanol to produce fuel cell grade hydrogen. Optimum operating conditions with appropriate composition of catalyst has been found to produce more selective hydrogen with minimum carbon monoxide. The reaction mechanism has been proposed based on the product distribution. The kinetic model available in literature fitted well with the experimental results.

The cold-start behavior and the effect of subzero temperatures on fuel cell performance were studied using a 25-cm 2 PEMFC. The fuel cell system was housed in an environmental chamber that allowed the system to be subjected to temperatures ranging from sub-freezing to those encountered during normal operation. Fuel cell cold-start was investigated under a wide range of operating conditions. The cold-start measurements showed that the cell was capable of starting operation at −5 °C without irreversible performance loss when the cell was initially dry. The fuel cell was also able to operate at low environmental temperatures, down to −15 °C. However, irreversible performance losses were found if the cell cathode temperature fell below −5 °C during operation. Freezing of the water generated by fuel cell operation damaged fuel cell internal components. Several low temperature failure cases were investigated in PEM fuel cells that underwent sub-zero start and operation from −20 °C. Cell components were removed from the fuel cells and analyzed with scanning electron microscopy (SEM). Significant damage to the MEA and backing layer was observed in these components after operation below −5 °C. Catalyst layer delamination from both the membrane and the gas diffusion layer (GDL) was observed, as were cracks in the membrane, leading to hydrogen crossover. The membrane surface became rough and cracked and pinhole formation was observed in the membrane after operation at subzero temperatures. Some minor damage was observed to the backing layer coating Teflon and binder structure due to ice formation during operation.