Catalyst decal transfer

Catalyst decal transfer [6, 78] In the catalyst decaling method, the catalyst ink is cast onto a PTFE blank for transfer to the membrane by hot pressing. A thin CL is left on the membrane when the PTFE blank is peeled away. Finally, the catalyzed membrane is re-hydrated and ion-exchanged to the if form by immersing it in hot dilute H2SO4 solution. 

As we discussed above, there are two major types of CL fabrication techniques. One is to apply the catalyst ink onto the gas diffusion layer to form a catalyzed diffusion medium (CDM), and the other is to apply the catalyst ink onto the PEM to form a CCM. Normally, applying the ink to the gas diffusion medium has the advantage of preserving the membrane from chemical attacks by the solvents in the catalyst ink. However, it seems that the CL does not come into close contact with the membrane and therefore the electrode is prone to delamination. Regarding CCM, there are two ways of applying the catalyst ink to the membrane, namely the decal transferring process and the direct coating process. In the former, the CL is cast onto a PTFE blank... 

In most industrial processes, the electrodes are prepared from a so-called ink consisting of the supported catalyst powder, ionomer, and additives. Already here, the chosen carbonaceous support material will affect the ink properties, such as homogeneity and viscosity, and therefore necessitate adapted ink recipes for each support material. The ink is then either airbrushed, sieve-printed, inkjet-printed, or DECAL transferred onto the membrane or the GDL and - like the ink ingredients - also the chosen manufacturing process strongly affects the electrode properties. 

Membrane-based Hydrophilic Catalyst Layer. Wilson and Gottesfeld [8, 21-23] suggested an ionomer-bonded hydrophilic catalyst layer prepared with the decal transfer method. The so-called decal transfer process includes two key steps (1) coating catalyst ink onto a blank substrate (e.g., PTFE film) then (2) transferring the coat onto the membrane (as shown in Figure 19.6). A typical preparation procedure is as follows ... 

Suzuki, T., Tsushima, S., and Hirai, S. 2011. Effects of Nafion ionomer and carbon particles on structure formation in a proton-exchange membrane fuel cell catalyst layer fabricated by the decal-transfer method. 36, 12361-12369. 

Recently, a modified decal transfer technique for CCM fabrication was reported [55]. In this method, a colloidal catalyst ink was used, as described by Uchida [56]. First, the ink was coated onto a Teflon substrate. After drying, the CL was transferred to a H" " form membrane (e.g. Nafion 112 membrane) by hot pressing at 120-135 °C. Finally, the Teflon substrate was peeled off the CCM. 

Aside from the above process, a decal transfer method has also been developed to make a thin-film electrode [81-83]. The catalyst ink is first coated onto a decal substrate (such as PTFE film or Kapton film) by spraying or by using the doctor blade technique. The catalyst ink is then transferred to a Nafion membrane by a hot-pressing process to form a catalyzed membrane. This decal transfer method is presented schematically in Fig. 2.15 [83]. 

Decal Method In this technique, thin CLs are cast or spread onto a nonadhesive medium, and decal transferred onto an electrolyte by hot-press compression (similar to a clothes iron). This method is suitable for mass production of catalyst layers, with high tolerance and batch processing capability, although the physical bond between the electrode and the electrolyte must be carefully maintained. 

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]. 

As seen in Fig. 22, ME As based on such thin-film catalyst layers can be constructed using a decal process, in which the ink is cast onto Teflon blanks for transfer to the membrane by hot-pressing. A second approach is to cast the same type of ink (TBA+ form of the ionomer) directly onto the membrane [12]. The latter process has an advantage over the decal process in... 

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