An essential part of proton exchange membrane fuel cells (PEMFCs) is the gas diffusion layer (GDL), which provides pathways for by-products to be removed from PEMFCs. One of the main properties of GDLs is porosity. The two widely used experimental methods for finding the porosity of GDLs are mercury intrusion porosimetry (MIP) and method of standard porosimetry (MSP). In addition to these methods, the porosity of GDLs can be calculated based on the high resolution 3D images that are acquired using X-ray microtomography (μXCT) as shown in recent studies (e.g., [7,12]). Despite the general success of using μXCT to measure GDL porosity, different porosity values have been reported for similar GDLs. These variations are due to different assumptions made for determining the surface of the sample, and hence, its external dimensions. In this research, current methods used for calculating porosity of GDLs from μXCT images are discussed, and a new surface identification method based on a rolling ball algorithm is introduced. The main advantage of this new method is that variations in surface topology or roughness are taken into account when calculating porosity. The new method is not only applicable to GDLs, but can be applied to characterize a wide range of highly porous media.

The gas diffusion layers (GDLs) are key components in proton exchange membrane fuel cells and understanding fluid flow through them plays a significant role in improving fuel cell performance. We used a combination of multiple-relaxation time (MRT) lattice Boltzmann method (LBM) and X-ray micro tomography imaging technology to compare results on dependence of the permeability calculation on the different system size of the computational gas diffusion layer sample. The micro-structures of the carbon paper (HP_1.76) and carbon cloth (HP_1.733) GDL were all digitizing 3D images acquired by X-ray computed micro-tomography at a resolution of 1.76 and 1.733 microns meter respectively, and the fluid flow was simulated by applying pressure gradient in both the through-plane and in-plane direction respectively. The lattice Boltzmann method for permeability calculation has already been tested in our previous work. In this work, we will focus on the permeability calculation of the realistic gas diffusion layer samples depend on the different size samples. The results show the permeability increases with fluctuations as the porosity rises. All the permeability and porosity converge to the value of large size sample that can be regarding a representative volume element. As the porosity and permeability of these Porous samples differs significantly for each other, the anisotropic permeability is nearly same for each one. We can choose part of the sample to calculate the characters if the sample is too big to calculate. We systematically study the effect of system size and periodic boundary condition and validate Darcy’s law from the linear dependence of the flux on the body force exerted.

High quality through-plane images of an operating polymer electrolyte membrane fuel cell (PEMFC) were visualized by employing synchrotron X-ray radiography to quantify liquid water in gas diffusion layers (GDL). Two types of GDLs, Toray carbon paper with and without micro-porous layers (MPLs), were employed and imaged during the operation. Performance data and x-ray images of these GDLs are compared to determine the impact of an MPL on water management. At low current density (<0.4A/cm 2 ) under high stoichiometric ratio, the MPL has little overall effect, but may behave as a diffusion barrier for reactants. At higher current density (0.6A/cm 2 ) and under low stoichiometric ratios, the MPL is observed to significantly affect the water management of the PEMFC and is credited for increased cell performance.

A greater understanding of nickel reduction-oxidation cycling (redox) mechanisms at the microstructural level can enhance SOFC performance and reliability. Transmission x-ray microscopy (TXM) provides several techniques for exploring oxidation states within SOFC electrode microstructure. X-ray nanotomography and full field x-ray absorption near edge structure (XANES) spectroscopy are new TXM techniques that have been applied in tandem to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct Ni and NiO regions. XANES spectra for the individual materials provide a basis for the processing and analysis of these mixed samples. Images of composite samples obtained using x-ray nanotomography are treated using numerical image processing steps including: scaling, tomographic reconstruction, and image alignment and subtraction. The distinct nickel and nickel oxide phases have been uniquely identified using full field XANES nanotomography. Applications to SOFC anodes are discussed.

In this paper, through-plane liquid water distribution is analyzed for two polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). The experiments were conducted in an ex situ flow field apparatus with 1 mm square channels at two distinct flow rates to mimic water production rates of 0.2 and 1.5 A/cm 2 in a PEMFC. Synchrotron radiography, which involves high intensity monochromatic X-ray beams, was used to obtain images with a spatial and temporal resolution of 20–25 μm and 0.9 s, respectively. Freudenberg H2315 I6 exhibited significantly higher amounts of water than Toray TGP-H-090 at the instance of breakthrough, where breakthrough describes the event in which liquid water reaches the flow fields. While Freudenberg H2315 I6 exhibited a significant overall decrease in liquid water content throughout the GDL shortly after breakthrough, Toray TGP-H-090 appeared to retain breakthrough water-levels post-breakthrough. It was also observed that the amount of liquid water content in Toray TGP-H-090 (10%.wt PTFE) decreased significantly when the liquid water injection rate increased from 1 μL/min to 8 μL/min.

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.

In order to investigate the effect of microstructure of PEMFC porous layers on the liquid water behavior, liquid water accumulation and discharge behavior in the operating PEMFC was visualized by soft X-ray radiography. The utilization of low energy X-ray made it possible to detect the liquid water behavior in the porous layers with high temporal and spatial resolution, and the cross-sectional imaging can resolve the each components of the PEMFC. The visualization results showed that the liquid water distribution in the carbon paper and the carbon cloth GDL was completely different. The liquid water in the carbon cloth GDL concentrates at the weaves of fiber bundle and was effectively discharged to the channel. In addition, to investigate the effect of the network of pores in more detail, stereo imaging of the liquid water evaporation process from the carbon paper GDL was carried out. These visualization results suggested that the microstructure of the PEMFC porous layers strongly affect the liquid water behavior in the PEMFC.

Heterogeneous dielectric material systems and their interfaces which are engineered at the local level (atomic/nano/micro scale) present special challenges for analysis and interpretation of their macroscopic functional behavior in response to specific operational histories. In addition to the chemical composition of the material, the local morphology plays a definitive role in the determination of the transport, electrochemical, and mechanical functions of the heterogeneous constituents, and especially in their interaction and collective action. The basic science of the effect of morphology on polarization, resulting multi-physics properties, and their evolution processes (which determine durability and life) are less well understood. The present paper will focus on a small part of this broader problem. Specifically, the effect of porous microstructure on the broadband dielectric characteristics of the solid oxide fuel cell (SOFC) will be discussed. Different variations of microstructure (such as porosity, pore connectivity, distribution, geometry etc) of YSZ based SOFC materials will be studied using a broadband dielectric spectroscopy system at different temperatures. A finite element based meso-to-continuum model (mm scale model with micron scale features) will be developed to predict dielectric characteristics (voltage, current, impedance distribution) utilizing actual morphology (captured via a 3D X-ray tomography microscope). The paper will summarize all preliminary results from the ongoing research and provide a pathway towards a robust analysis that will help design better microstructures for SOFC electrodes.

To observe the liquid water distribution in porous layers of an operational Proton Exchange Membrane Fuel Cell (PEMFC) with high spatial and temporal resolution, Laboratory-based soft X-ray microscopy has developed. This system can generate low energy X-ray in the soft X-ray range, and maximum sensitivity towards water is achieved. A point X-ray source with a diameter of less than 1.0 μm and the improved detector optics contribute to realize a spatial resolution of 500 nm and a temporal resolution of 1.0 sec/frame. In addition, in-plane and through-plane observations of an operational PEMFC were carried out. In the in-plane observation test, non-uniform distribution of liquid water in the plane of the catalyst layer was observed, and the importance of appropriate design of the catalyst layer to liquid water transport phenomena was suggested. In the through-plane observation test, liquid water discharge behavior near under the rib area was observed, and the importance of channel wall wettability to liquid water transport phenomena was also suggested.

In the current work, a lattice Boltzmann method (LBM) is developed to study the fluid flow through digitally reconstructed 3D models of carbon paper GDLs generated by x-ray computed tomography, and the research on permeability calculation in the gas diffusion layer is also included. The methods involves the generation of a 3D digital model of a carbon paper GDL as manufactured using x-ray images acquired through x-ray micro-tomography at a resolution of 1.74 microns. The reconstructed 3D images then read into the LB model in order to predict three orthogonal permeability tensors when pressure is prescribed in the different flow direction. The Lattice Boltzmann method (LBM), an evolving pore-scale modeling approach, has received increasing attention in computational fluid dynamics. In the LBM, fluid is represented by a distribution of particles moving on a regular lattice. The LBM is extremely appealing in porous medium simulation, because the bounce-back boundary condition is efficient to treat solid boundary. It can deal with the boundary condition more easily than other tradition method. At the inlet/outlet boundaries, a pressure boundary condition is applied. This study characterizes the relationships between anisotropic permeability and porosity for gas diffusion layer, where hydrodynamics is analyzed in detail. The results indicate that the LBM is powerful and is able to provide excellent estimation on the permeability in a porous medium. The calculated permeability is in good agreement with existing measurements. The relationship between the permeability and the porosity is fitted well with the Kozeny-Carman equation and existing results.

During operation of Polymer Electrolyte Membrane Fuel Cells (PEMFCs), electro-chemical reactions generate water, which exists as a liquid because of the PEFMC’s low operating temperature. The water remains in the PEFMC after it is turned off. During the winter this water can freeze; associated increase in its volume deforms the gas diffusion layer (GDL). The deformed GDL reduces the cell’s power output and durability. In this investigation, X-ray microscopy was used demonstrate that water freezing changed the geometry of GDL by water freezing.

Liquid water distribution in the operational PEMFC was visualized by soft X-ray radiography. To achieve a maximum sensitivity towards liquid water, low electron beam energy in soft X-ray range was chosen. As a result, the spatial resolution of 1 μm and the temporal resolution of 0.5 sec were obtained. In addition, a correlation between the accumulation of water and the reduction of performance in higher current density range was observed. At low current densities, liquid water accumulation was observed under the ribs, because the longer diffusion length for the rib area conduced to a less effective water removal into the vapor phase. With increase of current density, liquid water was also observed under the channels and the reduction of performance with time was observed. These results suggested that the current density under the rib is much less than under the channel and the anisotropy of GDL and the geometry of flow field had a heavy impact on the liquid water distribution and the cell performance.

Pr 0.3 Sr 0.7 Co 0.3 Fe 0.7 O 3−δ (PSCF3737) was prepared and characterized as a cathode material for intermediate temperature-operating solid oxide fuel cell (IT-SOFC). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and electrical property measurement were performed to study cathode performance of the material. XPS and EXAFS results proved that oxygen vacancy concentration was decreased and lattice constants of the perovskite structure material was increased by doping Fe up to 70 mol% at B-site of the crystal structure, which also extended the distance between oxygen and neighbor atom. Thermal expansion coefficient (TEC) of PSCF3737 is smaller than that of Pr 0.3 Sr 0.7 CoO 3−δ (PSC37) due to lower oxygen vacancy concentration. PSCF3737 showed better cathode performance than PSC37. It might be due good adhesion by a smaller difference of TEC between Gd 0.1 Ce 0.9 O 2 (CGO91) and electrode. Composite material PSCF3737-CGO91 showed better compatibility of TEC than PSCF3737. However, PSCF3737-CGO91 did not represent higher electrochemical property than PSCF3737 due to a decline of reaction sites by CGO91.

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.

We have investigated the effect of the recast temperature, i.e., heat treatment of a polymer electrolyte, on the diffusion coefficient and solubility of oxygen in the electrolyte and also on the morphological properties of recast ion-exchange membranes for improving the cathode activity in PEFCs. The recast membranes were prepared at different recast temperatures from Nafion ® and Aciplex ® solutions. Based on the chronoamperometric measurements, it was found that the diffusion coefficient and solubility of oxygen were deeply affected by the recast temperature. The diffusion coefficient increased with the decreasing recast temperature while the solubility had the opposite tendency. The water uptakes and ionic cluster size also varied with the recast temperature. Based on the X-ray measurements, it is considered that the differences in the mass transport parameters, the cluster sizes and water uptakes are due to the growth of clusters and crystallinity in the electrolyte.