Membrane preparation Nafion membranes

Run/Nin heteronuclear complexes such as (653), in which a photosensitizer [Ru(bpy)3]2+ or [Ru(phen)3]2+ is covalently attached to the Ni1 cyclam complex, have been synthesized in order to improve the efficiency of electron transfer from the photoexcited photosensitizer to the catalytic site.1 44-1646 However, these complexes did not perform particularly well, either due to unfavorable configuration of the Nin-cyclam subunit and the resulting steric hindrance or due to short lifetime of the excited states of the Ru photosensitizer moieties. A stable catalytic system has been prepared by immobilizing macrocyclic Ni11 complexes and [Ru(bipy)3]2+ in a nafion membrane.164... 

Nafion membrane Size-quantized Fe203 particles prepared in situ Photoelectron transfer was examined 672... 

An MEA with Nafion membrane was prepared by hot pressing (160°C, 96.5 bar, 2 min,) the double-sided ELAT electrode (20% Pt on Vulcan XC-72 and 0.5 mg/cm2 Pt loading) on the cathode side and carbon only electrode on the anode side. Prior to the MEA preparation, the Nafion membrane was purified using a standard procedure (Ticianelli, 1998). 

As shown in Figure 1.6, the optimized cathode and anode structures in PEMFCs include carbon paper or carbon cloth coated with a carbon-PTFE (polytetrafluoroethylene) sub-layer (or diffusion layer) and a catalyst layer containing carbon-supported catalyst and Nafion ionomer. The two electrodes are hot pressed with the Nafion membrane in between to form a membrane electrode assembly (MEA), which is the core of the PEMFC. Other methods, such as catalyst coated membranes, have also been used in the preparation of MEAs. 

The dependence of water uptake from the liquid phase on membrane thermal pretreatment was mentioned in the earliest descriptions of Nafion properties. As Grot et al. have pointed out [57], Nafion membranes take up dramatically more water from liquid water at very high temperatures-up to 100% of the polymer diy weight in the case of Nafion 120 when the membrane is in contact with liquid water at 180 °C. Such expanded ( E-form ) membranes maintain a constant, high water content when in contact with liquid water at temperatures at or below the pretreatment temperature. In contrast, S -form (S for shrunken) membranes are prepared by drying the membranes completely at elevated temperatures. Such membranes imbibe less water than as-received ( normal , N-form) membranes. 

Figure 24 shows a cross section of a Nafion membrane catalyzed by direct application of catalyst inks to its two major surfaces, as observed by SEM [52], The thin slice of MEA required for SEM imaging was generated by microtome from the MEA encapsulated in epoxy. This figure actually describes an MEA prepared for a DMFC, with PtRu black and Pt black catalyst layers of relatively high loading, resulting in catalyst layers 10 and 14 pm thick (Fig. 24). The SEM image well depicts two generic characteristics of CCMs prepared by direct, ink-based application of the catalysts to the ionomeric membrane the interface between the catalyst layer and the membrane is sharp on the SEM scale and the thickness of the catalyst layer measured from the...

Barnes et al. (112) considered the use of suifonate-ionomers, SPS and perfluorosulfonate membranes, as catalysts for carrying out chemical reactions. In a variation on this theme, Maurltz et al. have prepared unique mlcrocomposlte membranes by the In situ growth of silicon oxide in solvent swollen Nafion membranes. This work is described later in this book. 

The preparation of the supported catalytic Fe-clusters have been recently reported by our laboratory for Fe/Nafion membranes [1,2,3] for Fe/Nafion/glass-mats [4,5] micro-encapsulated Fe-alginate beads [6] Fe-amorphous polycrystalline thin film fused copolymers [7] and finally Fe/silica woven fabrics [8]. Experiments were conducted with Nafion perfluorinated cation transfer membrane. Photolysis experiments were carried out by means of a Hanau Suntest Lamp with tunable light intensity equipped with an IR filter to remove infrared radiation. Light... 

Fluorinated lonorner Membranes 341 Table 10.1 Properties of Nafion membranes prepared using different processes. 

Recently, several interesting studies of the electrochemical properties of electrodes coated with thin films of Nafion have been reported. These chemically modified electrodes are prepared using low-EW polymers which are alcohol soluble, or using a solution of a 1100-EW polymer which has been dissolved at high pressure and temperature. Electrochemical studies for cations such as the Ru(bpy)3 couple yielded estimates of ionic diffusion coefficients in the polymer films. However, results also indicate that these films are far more porous than conventional Nafion membranes, so it is not possible to compare values directly with those discussed above. 

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