Conductivity through-plane

Similarly to in-plane conductivity, through-plane conductivity seems to be a linear function of the compressed thickness of the DL that is, conductivity increases linearly with thickness decrease. Nitta et al. [216] also observed that in-plane conductivity was larger than through-plane conductivity however, the difference was not as large as that found in previous studies [9]. 

In fuel cells, through-plane conductivity is more meaningful than in-plane because the proton transfer occurs in the through-plane direction. Several methods have been developed to measure the through-plane conductivity, and these will now be described. 

A coaxial probe can also be used to measure the through-plane conductivity of membranes. Figure 5.15 shows the schematic for a coaxial conductivity measurement cell. In this method, the membrane is cut to the same size as the inner conductor, and the measured resistance is the through-plane resistance. The resulting conductivity, 2.4 x 10 2 S/cm, is close to that reported in the literature. 

Figure 5.15. Schematic cell for the measurement of through-plane conductivity [13]. (Reprinted from Journal of Electroanalytical Chemistry, 449, Gardner CL, Anantaraman AV. Studies on ion-exchange membranes. II. Measurement of the anisotropic conductance of Nafion , 209-14, 1998, with permission from Elsevier.)...

The through-plane conductivity ([Pg.211]

A instead of a linear increase in solids, we actually start to remove solids under these conditions. In addition to solids, we also measure through-plane conductivity, permeability, and numerous other characteristics as a function of the position in the gradient. The correlation of these characteristics to the formulation morphology is the goal of these experiments. 

For a GDM made of carbon fiber (e.g., carbon paper), the in-plane conductivity is normally much higher than the through-plane conductivity because most of the carbon fibers stay in the planar direction. Fortunately, since the thickness of the GDM is around 0.2 mm, the voltage loss caused by the through-plane resistance is not significant. For example, if the through-plane conductivity is 20 S cm then the voltage drop caused by one membrane electrode assembly (MEA) (with two pieces of GDM) will be 2 mV at a current density of 1 A cm. ... 

Theoretically, in an isotropic material in-plane and through-plane conductivities are supposed to be equal. However, in many bipolar plate materials the through-plane values tend to be... 

A fiber alignment method and conductive tie layer (CTL) have been proposed by Blunk et al. (2003) as a means of improving conductivity of composite bipolar plates (Figure 6.6). The authors have suggested a CTL which seeks to reduce the high contact resistance between the bipolar plate and the gas diffusion layer (GDL) interface. Even as the through-plane conductivity was improved by these processes, the... 

The proton exchange membrane (PEM) is a key component of PEM fuel cells. It separates the anodic and cathodic compartments and at the same time acts as a proton conductor by transporting protons generated at the anode to the cathode. The protons in the membrane are the main charge carriers. Hence, the conductivity induced by this proton transport is called proton conductivity. Because protons can get transported in two directions, both across and through the membrane, there are two types of conductivity in-plane and through-plane conductivities. The two types are theoretically different unless the membrane is isotopic in these two dimensions. In reality, the PEM is not an absolute electronic isolator. The electronic conductivity, normally much smaller than the... 

Typical bulk through-plane conductivity of Nafion as proton exchange membrane is around 0.1 Scm at 100% relative humidity (RH) and room temperature [24] with typical membrane thickness of 50-200 pm. In contrast, the conductivity of 0.5 M sulfuric acid as a common supporting electrolyte is on the order of 0.2 S cm . Anode to cathode spacing in a membraneless LFFC generally ranges from 0.5 to 1.5 mm, which results in higher total ohmic losses rather than PEM fuel cells. 

Component Typical Bulk Through-Plane Conductivity Oi or Typical Thickness Functional Dependencies... 

Another hot research topic about the PFSA proton conductivity is about the direction of the conductivity. There are two kinds of proton conductivity tangential/ in-plane conductivity and normal/through-plane conductivity. Commonly, proton conductivity is measured along the plane of the membrane, since the measurement of the conductivity in the in-plane direction is much easier to carry out with higher stability, reproducibility, and accuracy. However, in practice, the membrane requires proton conduction perpendicular to the manbrane. So, through-plane conductivity of the membrane may have significant effect on the performance of fuel cells. 

Without absorbing water, these PEMs tend to be rather rigid and are poor ionic conductors. The ionic conductivity would dramatically increase with water content [78]. Therefore, ionic conductivity tests are mostly conducted in water or in water vapor with adequate related humidity. Two types of ionic conductivity for PEMs were used in-plane and through-plane conductivities. The former represents the conductivity along the membrane surface direction, and the latter refers to the conductivity across the membrane thickness direction. In addition, there are two methods for conductivity measurement two-point probe electrode and four-point probe electrode. The latter method is more accurate but the former uses a simpler device. Therefore, comparison of ionic conductivities between membranes must be of the same type and measured through the same method. The aforementioned conductivity measurements are suitable for both proton conductivity and anion conductivity. Proton conductivity (o) is calculated by the following equation [79-82] ... 

The in- and through-plane electrical conductivities of the composites were measured by using traditional four point probe device Keithley 580 and a fixture designed in our laboratory for through-plane conductivity. Fig. 1 shows that the conductivity increases with the increase of the EG content. There are two sharp jumps, one at 35 wt% and the other at 75 wt% of EG. However, the mechanical strength of composites with EG content greater than 65 wt% was found to be poor. In view of this, the EG content was varied between 35 - 65 wt %. 

The improved through-plane conductivity was found to correspond with increased out-of-plane fiber orientation as shown in Table 2. In the table, 0 is the inplane (LW plane) angle made by the fibers with respect to the direction of flow and O is the out-of-plane (TL plane)... 

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