Dual catalyst layers

Su H, Jao T-C, Pasupathi S et al (2014) A novel dual catalyst layer structured gas diffusion electrode for enhanced performance of high temperature proton exchange membrane fuel cell. J Power Sources 246 63-67... 

The results have been compared with the earlier proposal of a dual-pathway mechanism for Cl oxidation, and, together with previous experimental and theoretical results, summarized in a comprehensive reaction scheme that explicitly includes also the (reversible) exchange between adsorbed species, dissolved product species in the catalyst layer, and similar species in the bulk electrolyte. The traditional dualpathway mechanism, where both the direct and indirect pathways lead to CO2 formation, has beenextended by adding a third pathway that accounts for formation and desorption of incomplete oxidation products. In the mechanistic discussion, we have focused on the role in and contribution to the Ci oxidation process of the formation/desorption and re-adsorption plus further oxidation of incomplete oxidation products. This not only leads to faradaic currents exceeding that for CO2 formation, but may result in additional COad and CO2 formation, via adsorption and oxidation of the incomplete oxidation products. 

Thin-film catalyst layers are usually hydrophilic, with no hydrophobic ingredients added inside the CL. Although PTFE is generally unnecessary for thin-film catalyst layers, sometimes hydrophobicity maybe required for better transport in the CL. Zhang et al. [11] designed a dual-bound composite CL that contained... 

Zhang and Shi [36] found that the dual-bound composite catalyst layer exhibited higher performance than either a PTFE-bound CL or a thin-film CL, as shown in Figure 2.9. Optimization of the dual-bound CL showed that impregnation of Nation between the two layers could lead to decreased cell performance [37]. Thus, the optimal structure for a dual-bound CL was a separate hydrophilic layer on top of a hydrophobic layer. 

Saha et al. [109] have proposed an improved ion deposition methodology based on a dual ion-beam assisted deposition (dual IBAD) method. Dual IBAD combines physical vapor deposition (PVD) with ion-beam bombardment. The unique feature of dual IBAD is that the ion bombardment can impart substantial energy to the coating and coating/substrate interface, which could be employed to control film properties such as uniformity, density, and morphology. Using the dual lABD method, an ultralow, pure Ft-based catalyst layer (0.04-0.12 mg Ft/cm ) can be prepared on the surface of a GDL substrate, with film thicknesses in the range of 250-750 A. The main drawback is that the fuel cell performance of such a CL is much lower than that of conventional ink-based catalyst layers. Further improvement... 

Zhang, X., and Shi, P. Dual bonded catalyst layer structure cathode for PEMFC. Electrochemistry Communications 2006 8 1229-1234. 

An important supplementary tool for performance analysis of PEFC electrodes is the study of the complex impedance, as it provides a tool to monitor changes of electrode function upon variation of its composition. It can help to detect in real time the structural changes due to spontaneous or current-induced repartitioning of the elements of the porous dual percolation network, that could lead to phase segregation and catalyst layer degradation. 

In some of the cases listed in Table 3.1 catalytic membranes are used. For instance the catalytic membranes prepared by Peters et al. (2007) have a catalyst layer deposited on a composite hydrophilic membrane. The dual-layer structure allows the independent optimization of the selective and the catalytic properties and partially satisfies contradicting material properties , such as the necessity to achieve a low permeability of the reactants together with a high availability of the same reactants on the catalyst. The value of 5 can be varied by changing the number of dip-coat... 

The GDL is usually made of a carbon-based porous substrate, such as carbon paper or carbon cloth, with a thickness of about 0.2 to 0.5 mm and a dual-layer structure. A schematic of the GDL between the flow field and the catalyst layer is presented in Figure 1.13. The first layer of the GDL, in contact with the flow field and the inlet gas in the flow channels, is a macro-porous carbon substrate, serving as a current collector, a physical support for the catalyst layer, and an elastic component of the MEA. The elastic component is necessary for the fuel cell to handle the compression needed to establish an intimate contact. The second layer of the GDL, in contact with the catalyst layer, is a thiimer microporous layer consisting of carbon black powder and some hydrophobic agent, which provides proper surface pore size and hydrophobicity to avoid flooding and to enhance intimate electronic contact at its interface with the catalyst layer [33]. 

Regarding the inherent problems with proton/gas transport for the hydrophobic or hydrophilic types of catalyst layers, a dual-bonded composite CL was suggested first by Zhang et al. [50, 51] in order to alleviate the drawbacks and promote the merits of the individual CL. Zhang and Shi [52, 53] also investigated such dual-bonded composite CLs by optimizing various components used. This dual-bonded CL cathode has two layers. The first is the hydrophobic layer with PTFE as a binder material, which is fabricated directly on the surface of the GDL. The second is a hydrophilic layer with Nafion as a binder material, which is fabricated on top of the hydrophobic layer surface. The typical preparation process can be summarized as follows ... 

Jusys, Z., Kaiser, J. and Behm, R. J. A novel dual thin-layer fiow cell double-disk electrode design for kinetic studies on supported catalysts under controlled mass-transport conditions . Electrochimica Acta 49,1297-1305 (2004). 

Then add a bit of NaHCOs (4 grams) and salt to saturate solution. Stir a bit more. Separate layers, Extract one more time and distill. Time depends on reaction speed. Reaction speed depends on the amount of catalyst and temperature. 60 C seems to be good, more catalyst, less time. More temperature May be more byproducts, this is what happen when acetic acid is the solvent. Probably a good way will be also acetic acid and 40-50 C, but dual phase is easy to extract ans uses less chemicals. 

Heterogeneous tandem catalysis involving at least one of the components being supported has also been reported [178, 179]. For example, calcosilicate has recently been used as an effective carrier for simultaneous immobilisation of a dual-functional system based on a bis(imino)pyridine iron compound and a zirconocene to form a heterogeneous catalyst precursor. On activation with triethylaluminium, ethylene was converted to LLDPE the layered structure of the calcosilicate was used to account for the improved thermal stability and higher molecular weights of the LLDPE formed [179],... 

Frost et al. [35] anticipated the use of gradients in more than one component for fhe electrode (e.g., catalyst and Nafion) in the manufacture of electrodes by screen printing. Kim et al. [29] designed a dual CL as shown in Figure 2.7. Both anode and cathode contained two subcatalyst layers, each of which... 

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