Catalyst-coated membrane conventional

Catalyst layer ink can be deposited on gas diffusion layers to form a CCGDL, as discussed in the previous section. Alternatively, the catalyst ink can be applied directly onto the proton exchange membrane to form a catalyst-coated membrane (CCM). The most obvious advantage of the CCM is better contact between the CL and the membrane, which can improve the ionic connection and produce a nonporous substrate, resulting in less isolated catalysts. The CCM can be classified simply as a conventional CCM or as a nanostructured thin-film CCM. 

The nanostructured thin-film electrode was first developed at 3M Company by Debe et al. [40] and Debe [41], who prepared thin films of oriented crystalline organic whiskers on which Ft had been deposited. The film was then transferred to the membrane surface using a decal method, and a nanostructured thin-film catalyst-coated membrane was formed as shown in Figure 2.10. Interestingly, both the nanostructured thin-film (NSTF) catalyst and the CL are nonconventional. The latter contains no carbon or additional ionomer and is 20-30 times thinner than the conventional dispersed Pt/ carbon-based CL. In addition, the CL was more durable than conventional CCMs made from Pt/C and Nation ionomer [40]. 

FIGURE 3.28 Cross-sectional SEM images of MEAs prepared by conventional, catalyst-coated membrane (CCM), and CCM hot-pressed methods, taken before and after long-term operation, (a) Conventional—fresh, (b) Conventional—1000 h, (c) CCM—fresh, (d) CCM—1000 h, (e) CCM hot pressed—fresh, and (f) CCM hot pressed—500 h [97]. 

Esterification/ alkylation, deNOx reaction, hydrogenation, and Zeolite molecular sieve membrane It is found that zeolite membranes, disk, and coating show high performance or potential as catalysts compared with conventional catalysts [160]... 

A concentration of the platinum loading close to the electrolyte interface via Pt-covered polymer nanofibers has been proposed by 3 M [31]. The concentration of the platinum catalyst coated onto nanofibers within approximately 300 nm distances from the electrolyte membrane surface, however, is leading to specific operation characteristics. While high power densities can be achieved under comparatively dry operating conditions even at elevated temperatures, the thin catalyst layers show a tendency for flooding under wet conditions at low temperatures. A summary of the behavior of this type of catalyst layers under specific operating conditions is given in [56]. The low temperature behavior has been improved by addition of a conventional catalyst layer on to this thin film catalyst layer [57]. 

It was reported that cobalt-tetraphenylporphyrin complex (CoTPP) coated on an electrode catalyzes electrocatalytic proton reduction,215 but the activity was not very high. We have found that metal porphyrins and metal phtahlocyanines when incorporated into a polymer membrane coated on an electrode show high activity in electrocatalytic proton reduction to produce H2.22,235 Some data are summarized in Table 19.2. It was shown that this catalyst is more active than a conventional platinum base electrode. 

PV is a promising option to enhance the conversion of reversible condensation reactions in which water is formed as a by-product. Peters et al. (2005) prepared composite catalytic membranes by a dip-coating technique. Composite catalytic membranes have been prepared by applying a zeolite coating on top of ceramic hf silica membranes. In the PV-assisted esterification reaction, the catalytic manbrane was able to couple catalytic activity and water removal. A reactor evaluation proved that the outlet conversion of the catalytic PV-assisted esterification reaction exceeded the conversion of a conventional inert PV membrane reactor, with the same loading of catalyst dispersed in the bulk liquid. Further, the performance of the zeolite-coated PV membranes can be increased by optimization of the catalytic layer thickness or by an increase in catalytic activity. 

Barbieri et al. [146] developed a MR for the WGS reaction. A palladium/silver fihn containing 23 wL% silver, which had a thickness between 1 and 1.5 pm, v is prepared by sputtering and coated onto a porous stainless steel support. This preparation method generated a much higher ratio of pore size to fihn thickness compared to conventional methods. Tubular membranes of 13 mm outer diameter, 10 to 20 mm length, were fabricated. Commercial Cu-based catalyst from Haldor-Topsoe was introduced into the fixed bed. At reaction temperatures between 260 and 300 C, and a GHSV of 2085 h, the thermodynamic equilibrium conversion could be exceeded by 5-10% by the membrane technology. 

In the two first cases the membrane is usually considered as catalytically inert and is coupled with a conventional fixed bed of catalyst placed on one of the membrane sides. In the case of reactor design based on an electrochemical cell configuration, the catalyst is coated on one of the electrodes or can serve as an electrode itself. 

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