Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Catalyst layer experimental studies

The macrohomogeneous model was exploited in optimization studies of the catalyst layer composition. The theory of composifion-dependent performance reproduces experimental findings very well. - The value of the mass fraction of ionomer that gives the highest voltage efficiency for a CCL with uniform composition depends on the current density range. At intermediate current densities, 0.5 A cm < jo < 1.2 A cm , the best performance is obtained with 35 wt%. The effect of fhe Nation weight fraction on performance predicted by the model is consistent with the experimental trends observed by Passalacqua et al. ... [Pg.414]

On the cathode side, on the other hand, the primary purpose of gas purge is to remove water from the cathode compartment, particularly in preparation for cold start from subzero temperatures. As gas purge defines the initial condition of water distribution in a cell, it is a crucial step in PEFC cold start. Recent experimental studies have amply shown that not only performance but also material durability of PEFC hinges strongly upon the gas purge process prior to cool down and cold start. This is because an effective gas purge can remove water from the catalyst layer and membrane, thereby creating space for water produced in cold start to be stored. [Pg.112]

To increase fundamental knowledge about ionic resistance, it is important to develop a methodology to experimentally isolate the contributions of the various cell components. Electrochemical impedance spectroscopy has been widely used by Pickup s research group to study the capacitance and ion conductivity of fuel cell catalyst layers [24-27] they performed impedance experiments under a nitrogen atmosphere, which simplified the impedance response of the electrode. Saab et al. [28] also presented a method to extract ohmic resistance, CL electrolyte resistance, and double-layer capacitance from impedance spectra using both the H2/02 and H2/N2 feed gases. In this section, we will focus on the work by Pickup et al. on using EIS to obtain ionic conductivity information from operational catalyst layers. [Pg.288]

Modern technological developments and many fields of pure and applied research depend on the quantitative information about the spatial element distribution in thin solid layers and thin-film systems. For example, without the use of thin films the experimental studies on the physics of semiconductor are very difficult. Similarly the diffusion processes in solids, sandwich-like thin films structures in microelectronics, anti-reflecting or selectively transparent optical films, catalysts, coatings, composites - all rely on material properties on an atomic scale. The development of these new materials as well as the understanding of the basic physical and chemical properties that determine their specific characters are not possible without the knowledge of their compositional structure, in particular in the interface regions. [Pg.89]

In catalytic slurry reactors the locale of the reaction is the catalyst surface. Hence, in addition to the mass transfer resistance at the gas-liquid interface a further transport resistance may occur at the boundary layer around the catalyst particle. This is characterized by the solid-liquid mass transfer coefficient, kg, which has been the subject of many theoretical and experimental studies. Brief reviews are given by Shah (82). In general, the liquid-solid mass transfer coefficient is correlated by expressions like... [Pg.234]

Theoretical and experimental studies of model bimetallic catalysts in recent years have distinguished between thermodynamically stable bulk alloys and so-called near surface alloys. Near surface alloys are materials where the top few surface layers are created in a chemically heterogeneous way, for example, by depositing a monolayer of one metal on top of another metal. These structures are often not the thermodynamic equilibrium states of the material. To give one example, Ni and Pt form an fee bulk solid solution under most (but not all) conditions,73 so if a monolayer of Ni is deposited on Pt and the system comes to equilibrium, all of the deposited Ni will dissolve into the bulk. There is, however, a considerable kinetic barrier to this process, so the near surface alloy of a monolayer on Ni on Pt(lll) is quite stable provided a moderate temperature is used.191 If the deposited monolayer in systems of this type has a tendency to segregate away from the surface, a common near surface alloy structure is the formation of a subsurface layer of the deposited metal.85 The deposition of V on Pd(lll) is one example of this behavior.192... [Pg.143]

In spite of the widely recognized importance of an advanced catalyst layer design, detailed structural data for catalyst layers are still scarce in the open literature on fuel cells [116, 117]. In one of the rare experimental studies, Uchida et al. showed the effect of the variation of the PFSI (and PTFE) content on catalyst layer performance [101]. An attempt to rationalize the experimentally observed composition dependence theoretically was first undertaken in Ref. 17. The prerequisites for an adequate theoretical study... [Pg.491]

The potential benefit of impedance studies of porous GDEs for fuel applications has been stressed in Refs. 141, 142. A detailed combined experimental and theoretical investigation of the impedance response of PEFC was reported in Ref. 143. Going beyond these earlier approaches, which were based entirely on numerical solutions, analytical solutions in relevant ranges of parameters have been presented in Ref. 144 which are convenient for the treatment of experimental data. It was shown, in particular, how impedance spectroscopy could be used to determine electrode parameters as functions of the structure and composition. The percolation-type approximations used in Ref. 144, were, however, incomplete, having the same caveats as those used in Ref. 17. Incorporation of the refined percolation-type dependencies, discussed in the previous section, reveals effects due to varying electrode composition and, thus, provides diagnostic tools for optimization of the catalyst layer structure. [Pg.498]

GDE and the diffusivity of oxygen in air. It was found through the fitting in [4] that a much larger value of So was needed to explain experimental results. The results suggested that significant oxygen mass transport losses occur in the catalyst layer. For the purposes of this study, So is taken as a fitted parameter. [Pg.325]

The catalyst, y-alumina is deposited in the microchannels according to a special experimental procedure, allowing a uniform catalytic layer in the channels [6]. The efficient use of the microchannel reactor for periodic operation at cycle periods as short as Is was evidenced in an experimental study [6]. [Pg.241]

The result of these degradation mechanisms is that that the GDL and the MPL both lose their hydrophobic character [133, 153, 154], and that the pore structure of the materials changes. The relation between microstructure and surface properties and mass transport properties has been the subject of several recent experimental studies [155,156], which indicate that indeed mass transport can be seriously affected by the hydrophobicity of the GDL and MPL as well as by the pore size. This will contribute to the gradual decay of the performance, though it is hard to distinguish the effects of changes in the GDL/MPL to those of changes in the catalyst layer. [Pg.287]

This coarse-grained molecular dynamics model helped consolidate the main features of microstructure formation in CLs of PEFCs. These showed that the final microstructure depends on carbon particle choices and ionomer-carbon interactions. While ionomer sidechains are buried inside hydrophilic domains with a weak contact to carbon domains, the ionomer backbones are attached to the surface of carbon agglomerates. The evolving structural characteristics of the catalyst layers (CL) are particularly important for further analysis of transport of protons, electrons, reactant molecules (O2) and water as well as the distribution of electrocatalytic activity at Pt/water interfaces. In principle, such meso-scale simulation studies allow relating of these properties to the selection of solvent, carbon (particle sizes and wettability), catalyst loading, and level of membrane hydration in the catalyst layer. There is still a lack of explicit experimental data with which these results could be compared. Versatile experimental techniques have to be employed to study particle-particle interactions, structural characteristics of phases and interfaces, and phase correlations of carbon, ionomer, and water in pores. [Pg.407]


See other pages where Catalyst layer experimental studies is mentioned: [Pg.975]    [Pg.975]    [Pg.25]    [Pg.73]    [Pg.464]    [Pg.467]    [Pg.498]    [Pg.513]    [Pg.43]    [Pg.210]    [Pg.252]    [Pg.251]    [Pg.16]    [Pg.170]    [Pg.282]    [Pg.286]    [Pg.504]    [Pg.2]    [Pg.470]    [Pg.23]    [Pg.84]    [Pg.399]    [Pg.686]    [Pg.994]    [Pg.1080]    [Pg.261]    [Pg.2976]    [Pg.367]    [Pg.657]    [Pg.190]    [Pg.331]    [Pg.384]    [Pg.390]    [Pg.428]    [Pg.439]    [Pg.93]    [Pg.216]    [Pg.261]   
See also in sourсe #XX -- [ Pg.251 , Pg.252 ]




SEARCH



Catalyst layer

Catalysts studied

Experimental studies

© 2024 chempedia.info