Direct methanol fuel cell anode catalyst layer

In electrochemical systems, metal meshes have been widely used as the backing layers for catalyst layers (or electrodes) [26-29] and as separators [30]. In fuel cells where an aqueous electrolyte is employed, metal screens or sheets have been used as the diffusion layers with catalyst layers coated on them [31]. In direct liquid fuel cells, such as the direct methanol fuel cell (DMFC), there has been research with metal meshes as DLs in order to replace the typical CFPs and CCs because they are considered unsuitable for the transport and release of carbon dioxide gas from the anode side of the cell [32]. 

Havranek A, Wippermann K (2004) Determination of proton conductivity in anode catalyst layers of the direct methanol fuel cell (DMFC). J Electroanal Chem 567(2) 305-15... 

Witham CK, Oran W, Valdez n, Narayanan SR (2000) Performance of direct methanol fuel cells with sputter-deposited anode catalyst layers. Electrochem Solid State Lett 3 497—500... 

Methanol (MeOH) crossover from the anode to the cathode in the direct methanol fuel cell (DMFC) is responsible for significant depolarization of the Pt cathode catalyst. Compared to Pt-based catalysts, NPMCs are poor oxidation catalysts, of methanol oxidation in particular, which makes them highly methanol-tolerant. As shown in Fig. 8.25, the ORR activity of a PANI-Fe-C catalyst in a sulfuric acid solution is virtually independent of the methanol content, up to 5.0 M in MeOH concentration. A significant performance loss is only observed in 17 M MeOH solution ( 1 1 water-to-methanol molar ratio), a solution that can no longer be considered aqueous. The changes to oxygen solubility and diffusivity, as well as to the double-layer dielectric environment, are all likely to impact the ORR mechanism and kinetics, which may not be associated with the electrochemical oxidation of methanol at the catalyst surface. Based on the ORR polarization plots recorded at... 

Figure 4.64. Mesoporous PtRu catalyst layer supported on a) RVC, b) UGF, and c) Ti mesh. Galvanostatic electrodeposition using micellar media based on Triton X-100. 20 A m 341 K [218], (With kind permission from Springer Science+Business Media Journal of Applied Electrochemistry, Direct methanol fuel cells with reticulated vitreous carbon, uncompressed graphite felt and Ti mesh anodes, 38, 2008, 51-62, Cheng T, Gyenge E, figure 7.)...

Abstract One of the most critical fuel cell components is the catalyst layer, where electrochemical reduction and oxidation of the reactants and fuels take place kinetics and transport properties influence cell jjerformance. Fundamentals of fuel cell catalysis are explain, concurrent reaction pathways of the methanol oxidation reaction are discussed and a variety of catalysts for applications in low temperature fuel cells is described. The chapter highlights the most common polymer electrolyte membrane fuel cell (PEMFC) anode and cathode catalysts, core shell particles, de-alloyed structures and platinum-free materials, reducing platinum content while ensuring electrochemical activity, concluding with a description of different catalyst supports. The role of direct methanol fuel cell (DMFC) bi-fimctional catalysts is explained and optimization strategies towards a reduction of the overall platinum content are presented. 

The ORR electrochemistry in gas saturated 0.05 mol dm" H SO was investigated at 25 °C using a platinum RDE, with or without organic impurities in the solution. These organic impurities are supposed to come into the cathode catalyst layer through the catalyst ink or MEA binders (2-propanol, Triton-X 100), from decomposition products from MEA binders and membranes (acetone, 1-hexanal, and 1-octanal) or from crossed-over anode fuel (methanol) through the polymer electrolyte in the case of direct methanol fuel cells. 

In 1997 and 1999 U.S. patents of Wilkinson et al. it was suggested that a multilayer electrode be used as the anode in DMFCs. The first layer consists of catalyst applied to carbon paper. Most of the methanol is oxidized in this layer. The second catalytic layer, applied directly to the membrane, already has a diluted methanol solution. Other ways of limiting methanol crossover are discussed in the next section when we discuss improvements in water management in fuel cells. 

This half-cell was used for evaluating methanol oxidation catalysts and catalyst layers [24], as described in the following section. It is expected that this cell could also be suitable to mimic fuel cell operating conditions for other liquid fuel oxidation because the WE structure is similar to the structure of the anode in a direct liquid fuel ceU. 

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