Alkaline fuel cells AAEMs

Figure 2.7 The outline of the AAEM alkaline fuel cell (cf. Figure 2.1).

The electrodes in PEM fuel cells contain a certain amount of Nafion polymer solution to act as a binder in the ink and also to introduce some H" conductive substance to the triple-phase boundary [74]. For AAEM fuel cells, there is a need for an analogous ionomer solution for use in the catalyst layer [54] and so it is an important consideration for development of good electrodes for the alkaline fuel cell [64]. 

Although most of the research in methanol fuel cells is performed in acidic PEM systems, substantial work is carried out in alkaline systems as well. Interestingly, methanol oxidation in alkaline media is, like hydrogen, more facile. In parallel to the PEM in acidic media, the anion alkaline exchange membrane (AAEM) is adopted for methanol electrooxidation in alkaline solutions. Like PEM, AAEM is also studied as a barrier for methanol crossover. 

Although the focus of this article is on PEMs that are being used in automotive fuel cells today, brief mention must be made of work carried out on alkaline anion exchange membranes (AAEMs). Such membranes have the potential to exhibit sufficient activity when used with non-precious metal catalysts, may work with fuels such as methanol and ethylene glycol and provide some of the features that commercial PFSA membranes provide for PEMFCs. A cross-linked, water-insoluble. 

Recent developments in AAEMs have opened up the possibiUty of an alkaline analog of the acidic solid polymer electrolyte fuel cell. This could utilize the benefits of the alkaline cathode kinetics and at the same time eradicate the disadvantages of using an aqueous electrolyte. As the AAEM is also a polymer electrolyte membrane (sometimes abbreviated as PEM), some clarity in abbreviations is required. In this chapter, PEM refers only to the proton exchange membrane fuel cells (acidic), AAEM refers to the anion exchange membrane H2/O2 fuel cells, and AFC exclusively refers to the aqueous electrolyte alkaline H2/O2 fuel cells. Anion exchange membranes are also employed in alkaline direct alcohol fuel cells, discussion of which will refer to them as ADMFC/ADEFC (methanol/ ethanol). 

The use of anion exchange membrane in fuel cells is a relatively nascent technology and as such has no Nafion-like industry leader that is ubiquitous in the field [51]. A recent review of alkaline membranes by Merle [52] highlights the vast number and variety of alkahne membranes in the literature, and the comparatively few commercially available membranes. As AAEMs are solid, they contain... 

As a new and underdeveloped technology, there is a shortage of examples of AAEM fuel cells in the literature. Some of the pioneering work in alkaline membranes and AAEM fuel cells come from the University of Surrey and the work of Varcoe and Slade [8,13,51,58,59,61,62,64-66,71,75-78]. They mainly use... 

They also developed a novel reference electrode for use in an AAEM fuel cell that allowed decoupling of the cathode and anode polarizations from the overall cell polarization. It was shown that the anode polarization was significantly higher than the cathode polarization, contrary to the situation in PEM fuel cells (Figure 2.12). In addition to the already discussed slower HOR kinetics in alkaline, it is thought that flooding in the anode of AAEM fuel cells can cause high mass transport polarization, even at low current densities (note that the thicker... 

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