**1. Introduction**

188 Corrosion Resistance

 The occurrence of pitting corrosion can be observed after 264 hours; pitting spots occur among previously localized brown spots. At one of the three electrodes, the paint

After 336 hours, in addition to the initial symptoms, few and very small points of

After 336 hours pitting corrosion occurs; the number of pitting spots is very small

After 192 hours pitting corrosion occurs in several points; on the electrodes with

 After 264 hours no major differences can be observed, the pitting points do not multiply After 336 hours uniform corrosion is observed on 2 of the 3 electrodes, with an immersion time of 60 minutes; on the electrodes with an immerse time of 5 minutes, the

In conclusion, from the three types of organic inhibitors studied, it can be said that 5,10,15,20 tetrakis(1-methyl-4pyridyl)21H,23H-porphine,tetra-p-fosylate salt, having the immersion time of 5 minutes was almost similar with the paint used and gives an anticorrosive protection much better than the porphyrin previously tested (H2TPP porphyrin (5,10,15,20 tetrakis 4 phenyl-21H,23H). Similar results can be seen, from the visual observations of the

Ahmad Z., (2006), Principles of Corrosion Engineering and Corrosion Control; *Institution of Chemical Engineers (Great Britain) - Elsevier/BH*, 656 pages ISBN 0750659246; Bose A., He P*.,* Liu C*.,* Ellman B.D.*,* Twieg R. J.*,*Huang S.D.*,* (2002), *Journal of the American* 

Monteiro PJ.M., Chong K.P., Larsen-Basse J., Komvopoulos K., (2001), Long Term Durability

Rahimi A., (2004), Inorganic and Organometallic Polymers, *Iranian Polymer Journal* 13 (2),

swells.

pitting are observed Electrodes treated as system I:

Electrodes treated as system II:

rust is adhering.

salt spray chamber test.

149-164;

*Chemical Society*, 124,4-5;

of Structural Materials, *Elsevier Science Ltd*.;

Standard practice for operating salt spray (fog) apparatus, B117-02

**5. References** 

**4. Conclusion** 

no changes can be observed after 24 hours or 48

After 264 hours signs of localized corrosion occur

no changes can be observed after 24 hours or 48

 After 120 hours the surface of electrodes become more matte After 192 hours the surface of electrodes become more rough

After 120 hours the surface of electrodes become more matte

immersion time of 60 minutes the number of pitting points is lower

Fuel cell is an electrochemical device which transforms chemical energy stored in fuel directly into electrical energy. The only by-products of this conversion are water and heat. The factors which affect the intensity of electrochemical processes include properties of the materials used for fuel cell components and its working environment. Due to insignificant emissions of pollutants during energy production combined with high efficiency of these generators, and silent operation, fuel cells are an alternative to technologies of energy production from fossil fuels.

 Studies on fuel cells today focus on extending their life, limitation of weight and size, and reduction of costs of manufacturing generators. Individual cell is composed of membrane/electrolyte and electrodes at both sides of MEA (membrane electrode assembly) (Fig. 1). The whole component is closed at both sides with bipolar or monopolar plates/interconnectors. Bipolar plates are the key components of generators since they take 80% of weight and 45% of costs of the cell [1].The task of the plates is to evenly distribute the fuel and air, conduct electricity between adjacent cells, transfer heat from the cell and prevent from gas leakage and excessive cooling.

According to DOE (the U.S. Department of Energy), basic requirements for materials for bipolar plates in fuel cells include in particular **corrosion resistance under fuel cell's operating conditions, low contact resistance, suitable mechanical properties, high thermal and electrical conductivity, low costs of manufacturing** [2]. Due to high material and functional requirements, few materials can meet these conditions. Bipolar plates in fuel cells are typically made of non-porous graphite because of its high corrosion resistance [3]. However, low mechanical strength of graphite and high costs connected with processing of graphite elevate the costs of manufacturing of fuel cells. Obtaining graphite-based composites modified with steel will allow for obtaining the material with improved mechanical properties, ensuring suitable corrosion resistance and high thermal and electrical conductivity at the same time. The method of powder metallurgy, which allows for obtaining even complicated shape of components, eliminates the problem of mechanical processing of graphite [4].

Properties of Graphite Sinters for Bipolar Plates in Fuel Cells 191

Bipolar plates/interconnectors in fuel cells typically have channels on their surface to allow for the distribution of media to the electrodes [29]. The shape of channels and direction of flow of media might be different for the plate adjacent to anode compared to the plate near cathode. Media which flow in to both electrodes can be supplied by means of parallel channels, where media flow in one direction or channels where media are supplied to fuel cells with opposite directions. Another possible solution is that the media flow in with the direction transverse to the cell. The choice and optimization of the shape of the channels in bipolar plates affect the operation of the cell, particularly the degree of removal of products and distribution of gases to the surface of electrodes. The figure below presents bipolar plates with channels (Fig. 3). The essential effect on operation of the cell is from the depth of

Review of the types of channels concerns in particular the geometry which depends on the type of fuel cell and demand for media in a particular cell. The list of opportunities for different channel design is obviously not ended and, apart from finding fundamental geometry, one should also consider the number of channels in the surface and distances between the channels. Proper distance between the channels and the number of channels ensure quick diffusion and effective discharge of water, especially in the cathode. **However, it should be emphasized that among a variety of types of channels used for distribution of media in fuel cells, there are no unequivocal research works which would have** 

Fig. 2. Materials for bipolar plates in fuel cells.

**provided evidence of which type is the best.** 

the channels, width of the channels, distance between spirals etc.

Fig. 1. Elements of fuel cell.
