Chapter 4 describes the modeling of the electrical conductivity of the composite bipolar plates for multi-component systems. Moreover, the performance of the developed composite bipolar plates was discussed at the end of the fifth chapter. Similarly, the effects of NG, CB and CF content on the properties of the composite bipolar plates were also studied.
Introduction
- Background
- Brief history of fuel cell
- Basic principle of fuel cell
- Different components of PEMFC
- Bipolar plate
- Types of bipolar plate
- Metal bipolar plates
- Graphite bipolar plates
- Carbon based composite bipolar plates
His exploration of the underlying chemistry of fuel cells laid the foundation for later fuel cell researchers. The hydrogen and oxygen gases are supplied to the anode and cathode by means of the flow field plates. Bipolar plate is one of the vital components of low temperature fuel cells, which can contribute up to 80% of the total weight of the PEMFC stack [Hermann et al., 2005].
Introduction | 13 selection considering the thickness reduction and ease of processing (flow field design) of the bipolar plate. However, the main disadvantage of the metal bipolar plate is the low corrosion resistance in the harsh acidic, humid and redox environment of the PEMFC. As a result, the lifetime and efficiency of the fuel cell is reduced [Davies et al., 2000].
However, plate metal corrosion and uneven expansion of the clad metal at fuel cell temperature are still limitations. The channels and ribs of the bipolar graphite plate made in this way are several millimeters.
Literature Review
Recent advances in composite bipolar plate
It was found that the mechanical strength of the composite is the highest under the same conditions. The authors did not achieve a significant improvement in the electrical conductivity and flexural strength of the composite. However, the through-plane electrical conductivity of the composite was significantly low at the optimal composition.
The authors performed the corrosion testing of the bipolar plate in a simulated fuel cell environment. However, the electrical conductivity of the developed bipolar plate was about 20 S·cm−1 which was quite low compared to the. According to the authors, other additives may further improve the performance and/or processability of the composite bipolar plate.
They also reported the biaxial flexural strength (not three-point flexural strength) of the composite bipolar plate as approximately 175 MPa. It was also expected to have high electrical and thermal conductivity of the clad composite bipolar plate. However, the electrical conductivity of the composite bipolar plates was not up to par.
However, the contact resistance of the composite was found to be comparable to that of the graphite. Likewise, the effect of CNTs on the porosity of the composite was not very significant. The in-plane electrical conductivity of the bipolar plate was 500 S·cm−1 with 40 wt% EG and 5 wt% CB.
However, the electrical conductivity of the composite was not yet sufficient to reach the US-DOE benchmark (Table 1.2). The maximum flexural strength of the composite was about 80 MPa with the in-plane electrical conductivity of about 230 S·cm−1. However, the anisotropy in the electrical conductivity of the composite material was more predominant in this case.
Summary of literature review
Electrochemical corrosion testing of the composite bipolar plate should be studied in the rigorous PEMFC environment to find the accelerated results due to aging of the composite. An overview of the comprehensive literature review on composite bipolar plate research and development is discussed in the following section. At the same time, electrochemical corrosion presents one of the major challenges in the selection of bipolar plate materials.
The thermal conductivity of the bipolar plate also plays a crucial role in the operation of the stack. It is noted that the vital properties of the bipolar plate are studied by researchers, but the available literature does not indicate that a particular bipolar plate has all the required properties. The various properties of the carbon-polymer composite bipolar plate reported in selected scientific and technical literature are listed in Table 2.2 based on the discussion in the literature review (section 2.1).
Table 2.2 shows that the electrical conductivity through the plane of the bipolar plate is hardly discussed. The literature review shows that the electrical conductivity in the plane of the bipolar composite plate has only been achieved. However, the goals for in-plane and through-plane electrical conductivity have not been achieved simultaneously by any of the cited literature.
Therefore, the electrical conductivity of the composite bipolar plate can be improved. However, graphite alone cannot offer sufficient properties as a bipolar plate filler suitable for PEMFC use. 2004) suggested that mixing polymers and preferentially locating a conductive filler in one of the polymer phases can increase the electrical conductivity of a composite bipolar plate. The table also shows that the electrical conductivities of the bipolar composite bonded to the thermoset resin are
The inclusion of nanomaterials is also expected to improve the through-plane electrical conductivity and reduce the anisotropy of the graphite-based composite bipolar plates. The mechanical properties of the composite bipolar plates can also be improved by the addition of any fibrous material [Mighri et al., 2004; Huang et al., 2005; The flexibility (deflection at midspan), H2 permeability, thermal conductivity and corrosion behavior of the composite bipolar plates should be thoroughly studied to develop composite bipolar plate suitable for fuel cell.
Aim and objectives
The detailed properties of the novolac PF resin used in the study are listed in table 3.1. The detailed properties of the resol PF resin used in the study are listed in table 3.2. In this investigation, Vulcan XC72 CB was used to improve the electrical property of the composite bipolar plates.
PAN-based CF in chopped form (about 2 mm in length) was used in the current study to achieve the target mechanical properties of the composite bipolar plate. The diagram of the manufactured bipolar plate is shown in Figure 3.3 along with the dimensions. The length (l), width (b) and depth (d) of the test subjects were measured using a caliper.
The thermal conductivity of the composite was measured using a Heat Conduction Unit (brand: Gunt, model: WL 370). Carmona and Ravier (2002) assessed the electrical conductivity of the CB-filled polymers using the percolation model. Therefore, the electrical conductivity through the plane of the composite bipolar plate was not taken into account in the model.
Therefore, another model was adapted to model the electrical conductivity of the composite bipolar plate with two-, three-, and four-component systems. But the electrical conductivity ratio of the fillers used to develop the bipolar plate is 104:59:10. The original GEM equation can effectively predict the electrical conductivity of a composite bipolar plate for such a complex assembly only if it is modified accordingly.
Electrical conductivity modeling | 95 electrical conductivity of the bipolar composite plate for different compositions and different fillers.
Results and Discussion
The effect of the molding temperature on the shore hardness of the composite was also investigated. The scleroscopic shore hardness of the composite bipolar plates was measured according to ASTM C886. The effect of the casting temperature on the scleroscopic Shore hardness of the composite bipolar plate is shown in Fig.5.24.
Therefore, the electrical conductivity of the composite bipolar plates was studied to evaluate the optimal molding temperature. The effects of NG content on the hydrogen permeability of the resin/NG composite bipolar plates are shown in Figure 5.27. The shore hardness of the composite bipolar plates was measured using a scleroscopic hardness meter.
However, the shore hardness of the bipolar composite plate was studied for all compositions. The effects of different filler contents on the thermal conductivity of the composite bipolar plates are shown in Fig. The thermal conductivity of the bipolar composite plate increased with the increase of NG content regardless of the resin type.
The effects of the scan rate on the corrosion current density of the composite bipolar plates are also shown in the respective figure. The corrosion current densities of the composite bipolar plates were accelerated in the severe fuel cell environments. The effects of CB content on the bulk density of the NG/CB/resin composite bipolar plates are shown in Fig.5.37.
The effect of CB content on the hydrogen permeability of the composite bipolar plate is shown in Figure 5.38. The effects of CB content on the corrosion current densities of the composite bipolar plates were shown in Fig. The effects of CB on the corrosion current densities of the composite bipolar plates in rigorously simulated PEMFC.
5.44(b) that the corrosion current density of the composite bipolar plates was more in the AFC environments. There was a small decrease in the thermal stability of the bipolar composite plate after CB reinforcements.
