Mechanism of CO poisoning

CO contamination is widely documented in the literature and recognized as a serious issue in the investigation of PEMFCs a decline in PEMFC performance is very often due to deactivation of the Pt anode catalyst, caused by traces of CO. Many attempts [14, 41, 42] have been made to use the EIS method to understand the mechanisms of CO poisoning and CO tolerance, by feeding an anode gas mixture of CO and H2. Examples of such studies will be discussed in detail in Chapter 6. 

Although there are alternative theories, the global reaction mechanism of CO poisoning of hydrogen PEFCs with platinum catalyst has been modeled by Springer and co-workers [79] ... 

During the investigation of CO poisoning in PEM fuel cell anodes, Ciureanu and Wang [14] compared in situ and ex situ measurements. They summarized three primaiy electrochemical methods that could be used for investigating the mechanism by which H2 and H2/CO mixtures are oxidized ... 

Lessons learned CO exposures and poisonings were the most dramatic health concerns in the early aftermath of the ice storm. CO toxicity has been documented as a health concern following winter storms, especially during power outages. Many of the same mechanisms observed in previous outbreaks of CO poisoning (e.g., improper use of gasoline generators and fuel-powered heaters) may have played a role in Maine. 

Many currently used drugs like acetyl salicylic acid, digitalis, nitrates, and quinine have existed for a long time, and so have many poisons like cyanide and neurotoxins. However, their mechanism of action was not known until the middle of 20th century or even later. CO is unique. The details of its mechanism of toxicity were published by Haldane as early as 1895 and subsequent work has only elaborated these details while affirming its correctness. The generation of COHb is the principal cause of CO toxicity however, it is not the only one. Much research has been done to elaborate these additional mechanisms of CO... 

A third approach to developing better fuel cell anodes is to study the kinetics and mechanisms associated with the reactions of suspected impurities in the reformate stream and various catalysts. The mechanism for CO poisoning of the anode catalyst is fairly well understood, but for other potential poisons that may not necessarily be the case. During this past year such a study has been initiated for hydrogen... 

The latter feature renders the Ap XANES a suitable technique to unravel complex reaction mechanisms and synergetic actions, as they are often active in bimetalhc catalysts. One example might be the bifunctional mechanism in CO poisoning of Pt-Ru fuel cell anodes, which will be discussed in detail below. 

S and Se, cause a dramatic increase in the rate of CO oxidation on Pt [101-104], similar to the case of CO-poisoned catalysts in heterogeneous catalysis [23, 44]. Both the EDL model of electrochemical promotion [23, 27] and rigorous ab initio quantum mechanical calculations [26] have shown that these pronounced promotional effects are due to the strong repulsive lateral interactions between adsorbed CO and coadsorbed electronegative adatoms [23, 26, 27]. 

Waugh, K. C., Butler, D., Hayden, B. E. (1994a). The mechanism of the poisoning of ammonia s3mthesis catalysts hy oxygenates O2, CO and H2O an in situ method for active surface determination. Catalysis Letters, 24, 197—210. 

The type of anode catalyst has a strong effect on the severity of CO poisoning, since the catalyst affects the kinetics of CO adsorption (equation (2.12) and equation (2.13)) and CO oxidation (equation (2.18) and equation (2.19)). Based on these mechanisms, many CO-tolerant electrocatalysts have been developed by Pt alloying, such as PtRu (platinum/ruthenium) [24,38], PtSn (platinum/tin) [39-41], and PtMo (platinum/molybdenum) [42-44]. Generally, alloying Pt with a second element can enhance the catalytic activity of the Pt through one or more of the following effects ... 

The mechanism of the poisoning effect of CO has been recognized in literature, especially those aiming at the exploring of CO-tolerant anode catalysts [37-40]. The poisoning process can be described as ... 

Slow anode kinetics and the problem of CO poisoning means that a major area of DMFC development involves the rmderstanding of the reaction mechanism and improving catalysts. Other problems with the DMFC include ... 

Figure 3.16 A possible mechanism for the removal of CO poisoning intermediates during methanol oxidation over Ti02 nanotube-supported Pt catalysts [55].

Not only 02 molecules but also other groups can be bound to the iron atom of hemoglobin. Specifically, carbon monoxide molecules can be so attached and, in fact, CO is more firmly bound to hemoglobin than is O2. This is one detail of the carbon monoxide poisoning mechanism. If we breathe a mixture of CO and 02 molecules, the CO molecules are preferentially picked up by the red blood cells. Since the sites... 

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