Catalyst degradation carbon corrosion

Young AP, Stumper J, Gyenge E (2009) Characterizing the structural degradation in aPEMFC cathode catalyst layer carbon corrosion. J Electrochem Soc 156 B913-B922... 

To widespread commercialization of PEMFC, as automotive application, 3000-5000 h of operation is demanded. However, presently, its maximum durability under automotive-operating conditions is roughly 1000 h [180], The physiochemical properties of ionomer, microstructure of Pt alloy catalyst, and carbon corrosion ultimately lead to degradation of MEA [181], Although there is no severe corrosion occurred in nonzero currents, much has been changed after PEMFC power cycle of start-up and shutdown operation for automotive applications [182,183]. Corrosion leads to performance degradation by reducing volume and connectivity of catalyst layer. 

Consequently, since graphitized carbon-supports have lower carbon corrosion rates, the use of cathode catalysts with graphitized supports significantly reduces H2/air-front start-stop damage.12,22 Furthermore, if the ORR activity of the anode electrode is reduced by lowering anode Pt loading, H2/air-front start-stop degradation is decreased.22,23... 

Pt catalyst ripening, electrocatalyst loss or re-distribution, carbon corrosion, electrolyte and interfacial degradation... 

It has also been shown that the Pt acts as a carbon corrosion catalyst [1,2], which likely localizes a significant portion of the carlxMi loss to areas in direct contact with Pt. Localized degradation has the potential to orphan Pt particles and expedite their dissolution, leading to severe decreases in the EGA and cell performance with time, akin to Fig. 24.3 where the electrode potential was forced to similarly high potentials. 

As a summary, we conclude that overall hydrogen starvation results in negative cell voltage and carbon corrosion in addition to water oxidation within the anode catalyst layer. Degradation reaction rates increase with decreasing fuel stoichiometry. 

A selective catalyst preferring water oxidation to carbon corrosion could reduce harmful catalyst support degradation since these undesired side reactions are concurrent processes, as explained in detail in Section 20.4. The preference of water electrolysis over carbon oxidation also requires enhanced water retention within the catalyst layer and therefore modifications of the gas diffusion materials. Promising developments are based on Pt/Ru catalysts [73]. 

Degradation and lifetime investigations are intended to characterize the membrane, the catalyst, and the corrosion of the carbon support as a function of time and... 

For the simulation of the degradation, the model accounts for the numerical feedback between the sub-models describing the non-aging mechanisms (e.g., water transport across the porous electrode) and the sub-models describing the aging mechanisms (e.g., carbon corrosion or catalyst dissolution in the case of PEMFCs) (Fig. 14). At each time step of the simulation, the performance part of the model calculates the... 

In total, electric energy, water, and heat are produced. However, additional and undesired reactions can produce catalyst layer degradation and consequently can limit the lifetime of the fuel cell. Carbon corrosion and dissolution of the active metal catalyst are the main undesired side reactions in PEFCs [62-66]. 

Carbon support corrosion in a fuel cell is another cause of catalyst degradation. Noble metals are usually supported on a high surface area carbon support to increase utilization of the metals. Carbon corrosion can take place according to Equation 21.46 ... 

Catalyst carbon support is thermodynamically unstable at PEMFC operating eonditions. Carbon corrosion can result in degradation of the catalyst layer. 

The membrane is typically negatively impacted by low humidity conditions, with the acceleration of mechanical failure observed. On the other hand, the catalyst layer durability is generally higher under drier conditions. The dominant degradation mechanisms of Ft dissolution and carbon corrosion are both accelerated under wetter conditions. 

In the introduction, it is mentioned that the use of carbon-based catalyst support materials leads to major degradation mechanisms, which are occurring during fuel cell operation. The most common known and well-understood phenomenon is carbon corrosion. According to (15.1), carbon gets oxidized with water to CO2 [17]. 

Acid contact accelerates carbon corrosion in all carbon components of the cathode. However, the high surface area and Pt-loaded carbons in the catalyst layer are significantly more prone to this degradation mechanism than the graphite of the bipolar plate. Nevertheless, this is considered and the plates will... 

Higher operational temperatures of HT-PEMFCs as compared to LT-PEMFCs impose more challenges with catalyst degradation. This issue coupled with the presence of free acid in the membrane obviously aggravates both carbon corrosion and platinum dissolution, which in turn triggers significant agglomeration of the... 

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