Catalyst layer performance evaluation

Equations (6.59)-(6.61) represent a highly simplified scheme for evaluating various catalyst layer designs. Refinements of this crude framework for evaluating catalyst layer performance should address all transport limitations, account for water accumulation, and include two- and three-dimensional effects. 

AID model for the physical evaluation of effects of structure and distributed processes on stationary catalyst layer performance requires a minimum of two... 

CL - icL Th crude framework for evaluating catalyst layer performance that was described in this section could be refined by including additional transport limitations, water accumulation, and higher dimensional effects. 

With both approaches, it is key to establish the current regions where samples are under kinetic control to allow the correct comparison. Many reported comparisons of catalysfs in MEA sfrucfures point to differences in performance, which are attributed to intrinsic catalyst differences when it is clear that differences are due to mass fransport effects because of catalyst layer structure. To help overcome these difficulties, it is recommended that, for catalyst evaluation, pure reactants be used (e.g., O2 instead of air) and at relatively high stoichiometries. Use of current-voltage curves should be corrected for elecfrolyte or membrane resistances and Tafel analysis used to identify fhe kinefically confrolled current regions. 

This section provides a comprehensive overview of recent efforts in physical theory, molecular modeling, and performance modeling of CLs in PEFCs. Our major focus will be on state-of-the-art CLs that contain Pt nanoparticle electrocatalysts, a porous carbonaceous substrate, and an embedded network of interconnected ionomer domains as the main constituents. The section starts with a general discussion of structure and processes in catalyst layers and how they transpire in the evaluation of performance. Thereafter, aspects related to self-organization phenomena in catalyst layer inks during fabrication will be discussed. These phenomena determine the effective properties for transport and electrocatalytic activity. Finally, physical models of catalyst layer operation will be reviewed that relate structure, processes, and operating conditions to performance. 

Electrodes were fabricated with catalyst layers containing platinum-ruthenium alloys and platinum-ruthenium oxide. Membrane electrode assemblies were fabricated with such cells, and the performance was evaluated in a full cell configuration. Although ruthenium oxide is a proton conductor and is expected to enhance the rate of proton transport from the interface during methanol oxidation, no noticeable improvement in activity of the catalyst layer was observed by addition of ruthenium oxide. The role of other metal oxides such as tungsten oxide will be investigated next year, along with evaluation of non-noble metal catalysts based on nickel, titanium, and zirconium. 

In order to estimate the input of the cathode catalyst layer on the MEA cell performance, each cell before testing in methanol solution has been evaluated in PEMFC operation conditions, namely with hydrogen on the anode side and oxygen or air on the cathode. Fig. 6 shows the dependencies of cell voltage and cell voltage compensated for membrane resistance vs. current density. 

UTC) has been using SiC for 50 years as an electrolyte matrix in PAFC because of its extreme stability in hot phosphoric acid. The system could not be used in fuel cell electrodes due to its poor catalytic activity and electrical conductivity. However, SiC has been evaluated as a catalyst support with addition of carbon black to enhance conductivity in the catalyst layer. The approach included the deposition of Pt particles on SiC by chemical route followed by mixing with carbon to formulate catalyst. Authors claimed that a higher Pt loading has led to improved electrode performance even with large particles of Pt. This indicated that electrode performance depends not only on surface area of Pt but also on the interaction nature between support and metal catalyst [19]. 

Yu and Ziegler [40] also employed an environmental scanning electron microscope (ESEM method) as a contact angle analysis tool to investigate hydrophobicity and hydrophilicity on inhomogeneous materials. They measured the contact angles of the catalyst layer before and after MEA evaluation, and found that the catalyst layer became more hydrophilic after MEA evaluation thus, this hydrophilic increase could be the cause of lower fuel cell performance. 

The single fuel cell test is one of the most direct and effective methods for the evaluation of catalyst layers and MEAs. Even if the results obtained by a half-cell test are very promising, the single-cell test is still a necessary step for performance validation of the developed catalyst layer and MEA. 

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