Electrodes and Electrode Structure

The best catalyst for both the anode and the cathode is platinum. In the early days of PEMFC development, this catalyst was used at the rate of 28mgcm of platinum. This high rate of usage led to the myth, still widely held, that platinum is a major factor in the cost of a PEMFC. In recent years the usage has been reduced to around 0.2mgcm, yet with power increasing. At such loadings the basic raw material cost of the platinum metal in a 1-kW PEMFC would be about 10 - a small proportion of the total cost. 

The basic structure of the electrode in different designs of PEMFC is similar, though of course details vary. The anodes and the cathodes are essentially the same too - indeed, in many PEMFCs they are identical. 

For the next stage, one of two alternative routes is used, though the end result is essentially the same in both cases. 

In the separate electrode method, the carbon-supported catalyst is fixed, using proprietary techniques, to a porous and condnctive material such as carbon cloth or carbon paper. PTFE will often be added also, because it is hydrophobic and so will expel the product water to the surface from where it can evaporate. In addition to providing the basic mechanical structure for the electrode, the carbon paper or cloth also diffuses the 

The second relates to the selection of the gas diffusion layer. We have seen that this is generally either a carbon paper or carbon cloth material. Carbon paper (e.g. ELAT , TORAY , and CARBEL are widely used brands) is chosen when it is required to make the cell as thin as possible in compact designs. In an interesting paper, Lee et al. (1999) 

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In addition to the development of electrodes and electrode structures, there are many options for the system and stack setup. Some patents and papers focus on the basic principles of the system, whereas other patents describe advantageous designs in detail. 

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