Poisoned electrode

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. 

To improve the response time, the surface of the solid-state membrane electrode can be polished to a luster with diamond paste or moist AI2O3 of particle size < 0.1 m-Poisoned electrodes can usually be restored by sanding and repolishing the surface. 

Caution is recommended when working with suspensions, so that sharp particles do not damage the relatively soft surface of the membrane. Poisoned electrodes can be regenerated with long periods of conditioning. In all other respects, including sample preparation, these electrodes closely resemble the homogeneous type. 

Unlike ion-selective electrodes using glass membranes, crystalline solid-state ion-selective electrodes do not need to be conditioned before use and may be stored dry. The surface of the electrode is subject to poisoning, as described earlier for a Ck ISE in contact with an excessive concentration of Br. When this happens, the electrode can be returned to its original condition by sanding and polishing the crystalline membrane. 

Ultradeep desulfurization of fuel oils is used for producing not only clean fuels but also sulfur-free hydrogen used in fuel-cell systems, in which the hydrogen can be produced potentially through the reforming of fuel oils. Fuel-cell systems must be run with little-to-no sulfur content, because sulfur can irreversibly poison the precious metal catalysts and electrodes used [12]. 

Interest in fuel cells has stimulated many investigations into the detailed mechanisms of the electrocatalytic oxidation of small organic molecules such as methanol, formaldehyde, formic acid, etc. The major problem using platinum group metals is the rapid build up of a strongly adsorbed species which efficiently poisons the electrodes. 

Adzlc et al (25) have shown that partial coverage of the electrode by adsorbed Pb can substantially reduce the effects of poisoning, presumably by blocking the surface sites required by the adsorbed CO. This is nicely confirmed by spectroscopic measurements. Figure 8... 

---