Toray paper

Figure 33. Visualization of liquid water transport in an operating transparent PEFC (45 /rm membrane with EW < 1000 GDL, Toray paper TGPH 090 with 20 wt % PTFE loading with a microporous layer).

Unlike the RDE technique, which is quite popular for characterizing catalyst activities, the gas diffusion electrode (GDE) technique is not commonly used by fuel cell researchers in an electrochemical half-cell configuration. The fabrication of a house-made GDE is similar to the preparation of a membrane electrode assembly (MEA). In this fabrication, Nation membrane disks are first hot-washed successively in nitric acid, sulphuric acid, hydrogen peroxide, and ultra-pure water. The membranes are then coated with a very thin active layer and hot-pressed onto the gas diffusion layer (GDL) to obtain a Nation membrane assembly. The GDL (e.g., Toray paper) is very thin and porous, and thus the associated diffusion limitation is small enough to be ignored, which makes it possible to study the specific kinetic behaviour of the active layer [6],... 

The activities of CNTs have been evaluated by Girishkumar et al. [7] using ex situ EIS. Their study was conducted in a three-compartment electrochemical cell using a GDE electrode (a carbon fibre paper coated with SWCNTs and Pt black as an anode or cathode). Electrophoretic deposition was used to deposit both the commercially available carbon black (CB) for comparison and the SWCNT onto the carbon Toray paper. Commercially available Pt black from Johnson Matthey was used as the catalyst. In both cases, the loading of the electrocatalyst (Pt), the carbon support, and the geometric area of the electrode were kept the same. EIS was conducted in a potentiostatic mode at either an open circuit potential or controlled potentials. 

FIGURE 10.28 Scanning electron microscopy (SEM) images of (a, b) Umbite and (c, d) ETS-10 supported on carbon Toray paper. (Erom Aused, M.P., Urbiztondo, M.A., MaUada, R., Pina, M.P., and Santamana, J., Synthesis of proton conducting membranes for direct metbanol fuel cells (DMPCs). Books of abstracts of tbe OSSEP Pinal Workshop, Tenerife, 2004, pp. 90-91.)... 

Chandra, B., Race, J.T., Sun, Y., Barton, S.C., and Hone, J. (2007) Growth of carbon nanombes on carbon Toray paper for bio-fuel cell applications. 

In addition to studying the performance of thin-film sputtered R electrodes, the effect of Teflon (PTFE) incorporation in the carbon Toray paper... 

For the investigation the oxygenated liquid fuels in half-cells, chemically prepared Pt-Sn (0.5 mg cm 8% Sn) and R-Ru (0.5 mg cm 50% Ru) electrodes supported on gas-diffusion type Vulcan XC-72/Toray paper were obtained from ETEK Inc. These electrodes generally have 15-20% PTFE content in the electrocatalytic layer. The electrochemically prepared electrodes consisted of electro-depositing R-Sn and R-Ru from an acid solution of hydrogen hexachloroplatinate(IV), tin(IV)chloride, and potassium pentachloro-aquoruthenate. 

The initial porosity of a carbon paper-type GDM is often higher than 75% (Toray paper and SGL paper as high as 80 and 90%, respectively). After teflonization, it may decrease to around 70%, which is still very high. The porosity of the GDM is measured by porosimetry, a technique ideal for measuring pores ranging from a few nm to a few hundred pm. The porosimeter first creates a vacuum condition to remove gases within the pores of the GDM,... 

Flow distribution patterns, (a) SGL sample. (b)Toray paper sample. The cross-hatched bars represent the distributions and the solid line the average value. (Source Kandlikar et ai, 2009a, with permission of Elsevier.)... 

Table 14.2 shows the porosities (pore volume per unit of sample volume) for hydrophilic pores Uphi, hydrophobic pores Upho, and the overall porosity u = Uphi + Upho for Toray paper with two values of PTFE concentrations cptee-Also shown in the table is the parameter hydrophobizing efficiency which represents the ratio of hydrophobic pores (in volume percent) to the PTFE concentration (in volume percent or, as carbon and PTFE have similar density values, in weight percent). This parameter is of importance since high values of the PTFE concentration can lead to an increase in the GDL s ohmic resistance. From the table it can be seen that the PTFE concentration does not significantly influence the volumes of both hydrophilic and hydrophobic pores. At the same time. 

TABLE 14.2 Porosity of Toray paper with different amounts of PTFE... 

Polymer-modified electrodes that are prepared by electropolymerization of monomers, with mediating properties toward NADH oxidation, are attractive because the synthesis is irreversible, the long-term stability of the electrode is enhanced, and the catalytic properties of the monomer are retained. A diversity of reports on electropolymerization of o-quinone derivatives [87-89], and phenothiazine and phenoxazine derivatives with different levels of utility for practical applications, can be found in the literature [62,65,66,68,72,90-92], Electropolymerization of azinc derivatives has mainly been reported on gold [66,91], platinum [93], glassy carbon electrodes [65,68,71,81,92,94-97], and other carbonaceous electrode materials (Toray paper [98-100], graphite [101], and screen-printed carbon [70]). 

In 2009, Treu et al. purified PQQ-dependent ADH from Gluconobacter and immobilized the enzyme with PQQ-dependent ALDH and high surface area nanotube supports on Toray paper with a hydrophobieaUy modified Nafion layer to bind the mixture to the surface [36]. With this type of eleetrode fabrication, the PQQ-dependent enzymes were able to achieve better eleetrieal eontact on the electrodes. This biologieal fuel anode with earboxylated single-waUed CNTs (SWCNTs) achieved the best result with a power density of 1.25mAem , a current density of 0.252 mAem , and an OCP of 1.15 V. Short and long earboxylated multiwalled nanotubes were also studied and all nanotube anodes showed inereased performance compared with earbon paper anodes without nanotubes. 

FIGURE 13.6 (a, b) S. oneidensis cells on Toray paper electrodes. Three-dimensional images prepared with Anaglyph Maker, ver. 1.08. Scale bars = 5 pm. (Unpublished images taken by author KEF.) 3D red cyan glasses are recommended to view this image correctly. 

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