Catalyst decaling method

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. 

Catalyst decaling In the catalyst decaling method described by Gottesfeld and Wilson (1992, 1992a) and Chun et al. (1998)... 

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]. 

Wilson, M. S. Membrane catalyst layer for fuel cells. US Patent 5,234,777,1993. Xie, J., Garzon, R, Zawodzinski, T., and Smith, W. Porosimetry of MEAs made by "thin film decal" method and its effect on performance of PEFCs. Journal of the Electrochemical Society 2004 151 A1841-A1846. 

Aside from being sprayed on the GDL, the catalyst ink can also be applied to the membrane to make a Nafion-bonded hydrophilic CL. To efficiently extend the three-phase reaction zone and reduce the Pt loading, Wilson et al. [37,39,41] developed a thin-fihn electrode using Nafion ionomer as the bonder. Their preparation process uses a decal method, the details of which are as follows [39] ... 

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 catalysts were tested as PEM fuel cell cathodic catalytic layers on a unit cell-test bench 50 cm Membrane-Electrode Assembhes (MEAs) were prepared by the decal method as described in reference [2]. The electrolyte was a Nafion membrane, and the anode a commercial anode made from Pt-doped carbon black (40 wt.%, TKK) deposited by Paxitech onto a carbon felt (0.6 mgpt cm mixed with Nafion ). The thickness of the cathode was kept constant by keeping constant the carbon mass in the catalytic layer. The Nafion /carbon mass ratio of the ink used to prepare the MEAs was fixed at 0.5. After a standardized start-up procedure, polarization curves, i.e. the t/ceii = f(/m) curves, were measured by setting the cell voltage at each desired value for 15 min, which... 

The second method for catalyzing the membranes is to cast the same type of ink (TBA" " form of the ionomer) directly onto the membrane [44]. This process may have an advantage over the decal process in the formation of a more intimate membrane/ electrode interface. It may also be more amenable to scale-up. Indeed, initial attempts at laboratory-scale automated application of thin-film Pt/C//ionomer catalyst layers to ionomeric membranes have been quite successful. In this work, a computer-controlled mechanism of an X-Y recorder was applied to paint catalyst ink by the controlled repetitive motion of the pen of the recorder onto each of the membrane major surfaces. In this way, 100 cm areas of catalyzed membranes were re-producibly generated, yielding performances per cm of a similar level to that achieved previously with catalyzed membrane of 5 cm active area [44]. The laboratory-scale automation equipment is shown in Fig. 22. 

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]. 

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