Catalyst layer membrane degradation

Performing EIS on fuel cells can help to identify potential problems or failures within the cell, such as catalyst coarsening, membrane degradation, bipolar plate corrosion, gas diffusion layer oxidation, and incorrect operating conditions. 

The dissolved Pt (Pt " ") either redeposits on Pt particles to form large particles or migrates out of the MEA into the membrane. Figure 10.29 shows Pt particles deposited within the membrane and near the catalyst layer/membrane interface after degradation [93]. These Pt particles originate from the dissolved Pt species at the cathode, which diffuse in the ionomer phase and subsequently... 

It is suggested that the Nafion ionomers inside the catalyst layer may degrade faster than the bulk manbrane owing to greater mechanical integrity of the membrane and the fact that the ionomers are located adjacent to the catalytic surface where H Oj/radicals are formed (Xie et al. 2005). This hypothesis was discussed by the authors, but there is no strong supporting experimental evidence. 

MEA performance is mainly limited by ORR kinetics, as well as oxygen transport to the cathode catalyst. Another major loss is due to proton conduction, in both the membrane and the cathode catalyst layer (CL). Characterization of the ionic resistance of fuel cell electrodes helps provide important information on electrode structure optimization, and quantification of the ionomer degradation in the electrodes [23],... 

Research on other types of materials for H2 separation has been motivated by relatively high cost of Pd and possible membrane degradation by acidic gases and carbon as summarized in Tsuru et al.76 These authors examined microporous silica membranes together with an Ni catalyst layer for SMR reaction. However, this type of membrane allows the permeation of hydrogen as well as other gases in reactants and products, which markedly reduces hydrogen selectivity and limits methane... 

Zhang S, yuan XZ, Cheng Hin JN, Wang H (2009) A review of platinum-based catalysts layer degradation in proton exchange membrane fuel cells. J Power Sources 194 588-600... 

There are various improvements that can be made to the presented model, some improvements could be accomphshed. Foremost among these possible future-work directions is the inclusion of nonisothermal effects. Such effects as ohmic heating could be very important, especially with resistive membranes or under low-humidity conditions. Also, as mentioned, a consensus needs to be reached as to how to model in detail Schroder s paradox and the mode transition region experiments are currently underway to examine this effect. Further detail is also required for understanding the membrane in relation to its properties and role in the catalyst layers. This includes water transport into and out of the membrane, as well as water production and electrochemical reaction. The membrane model can also be adapted to multiple dimensions for use in full 2-D and 3-D models. Finally, the membrane model can be altered to allow for the study of membrane degradation, such as pinhole formation and related failure mechanisms due to membrane mechanical effects, as well as chemical attack due to peroxide formation and gas crossover. 

Tmi Proton conductivity of bulk membrane at unit water content (SI cm" ) at Proton conductivity of a polymer electrolyte in the catalyst layer (SI cm" ) Ti Local time of degradation... 

Certain performance losses of fuel cells during steady-state operation can be fully or partially recovered by stopping and then restarting the life test. These recoverable losses are associated to reversible phenomena, such as cathode catalyst surface oxidation, cell dehydration or incomplete water removal from the catalyst or diffusion layers [85]. Other changes are irreversible and lead to unrecoverable performance losses, such as the decrease in the ECSA of catalysts, cathode contamination with ruthenium, membrane degradation, and delamination of the catalyst layers. 

Zhang S, Yuan X Z, Cheng Hin J, Wang H, Wu J, Friedrich K A and Schulze M (2010), Effects of open-circuit operation on membrane and catalyst layer degradation in proton exchange membrane fuel cells. Journal of Power Sources, 195,1142-1148. 

The reasons for the deterioration of ceU performance can be distinguished in reversible and irreversible power loss. Inevitable irreversible performance loss is caused by carbon oxidation, platinum dissolution, and chemical attack of the membrane by radicals [7]. Reversible power loss can be caused by flooding of the cell, dehydration of the membrane electrode assembly (MEA), or change of the catalyst surface oxidation state [8]. If corrective actions are not started immediately, reversible effects lead to irreversible power loss that we define as degradation. In this chapter, we focus on the degradation of the catalyst layer due to undesired side reactions. 

In order to develop durable membranes under low humidity conditions, it was of utmost importance that the degradation mechanism was understood. It was commonly beheved that the hydrogen peroxide formed in the catalyst layer diffuses into the membrane and subsequently the... 

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