Electrodes degradation

On the negative side, materials problems related to corrosion, electrode degradation, electrocatalyst sintering and recrystalhzation, and electrolyte loss by evaporation are all accelerated at higher temperatures. 

Another issue with platinum catalysts is that their capacity sometimes fades over time. Several factors are responsible, including a phenomenon similar to the side effects described for medications in chapter 3. Side effects occur when a medication acts on healthy tissue instead of the intended target. With platinum electrodes, the problem is that sometimes unwanted reactions occur at the electrodes. In the oxygen reactions taking place at the cathode, for example, hydroxide (OH) and other molecules sometimes form and bind to the platinum atoms. These molecules cover the platinum atoms and block access to the desired reactant, thereby reducing the catalytic activity. Sometimes the molecules even pull platinum atoms away from the surface, causing serious electrode degradation. 

Although several hypotheses have been proposed, the mechanisms of electrode degradation involved in shedding and inactivation processes are still not clear. The method of material preparation plays a substantial role here. For example, positive material prepared by oxidation of needle like crystals of tetrabasic lead sulfate HPbO PbS04) maintains the latter s morphology and the electrode s superior performance during cycling of stationary cells." ... 

The Structure of Memory Device Switching Material Substance Flexible Substance Transient Electrode Degradable Substance Voltage (V) Current Level (A) Retention On/Off Ratio References... 

Swathirajan S, Merzougui B, Yu PT Fuel cell and method for reducing electrode degradation during startup and shutdown cycles. US patent US 2008/0166599 Al... 

Track electrode degradation leading to activity decay... 

This chapter was focused on electrode degradation in PEMFCs for automotive application. It has been pointed out that undesired side reactions are responsible for the limited long-term stabihty of a fuel-cell system. These reactions occur at high electrode potentials which therefore have to be avoided. 

When there is no more lithium to be extracted fk>m the positive electrode, the electrode degrades, as does the electrolyte. The negative, which is often present in excess capacity in comparison to the positive electrode, does not present such dangers, at least at the beginning of its life. 

In fact, this potential driven corrosion of carbon can be quite severe, causing substantial loss of the electrochemically active surface area as the electrode degrades with the loss of the catalyst support. Enhanced fuel cell degradation can occur under the additional stress conditions associated with cold start and hot stopping [62]. 

PEMFCs are very clean systems and act as filters for impurities introduced from ambient air, fuel used, and even degradation products from the cell materials. Both the membrane and the catalyst are susceptible to cmitamination and poisoning. Electrode degradation of PEMFCs can occur as a result of various impurities found in the fuel feed, air stream, as well as corrosimi by-products from fuel cell components such as the bipolar plate, catalysts, or membrane. 

About the operation condition, details of nickel electrode degradation have been... 

Yokokawa et al. [8] made thermodynamic analyses on the interaction between cathodes/anodes and gaseous impurities. By comparison between the thermodynamic reactivity and the electrode degradation behaviors, they have extracted... 

Following the above description of the typical electrode construction, the actual used catalyst support materials and the electrode degradation mechanisms, the following section focuses on the fabrication of electrodes and MEAs. 

The two major mechanisms that will be referred to a number of times throughout this chapter are briefly introduced here, including cathode electrode degradation and membrane degradation. 

In addition to the increased water content of the electrodes, the membrane gas cross-over is also increased at a high membrane water content. This may accelerate electrode degradation mechanisms such as carbon corrosion due to partial fuel starvation, which is influenced by the cross-over of oxygen to the anode (see Section 6.4.2). 

Increased operating temperature will accelerate membrane and electrode degradation mechanisms (see Section 6.2.2). 

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