Carbon monoxide tolerance

There are three major gas reformate requirements imposed by the various fuel cells that need addressing. These are sulfur tolerance, carbon monoxide tolerance, and carbon deposition. The activity of catalysts for steam reforming and autothermal reforming can also be affected by sulfur poisoning and coke formation. These requirements are applicable to most fuels used in fuel cell power units of present interest. There are other fuel constituents that can prove detrimental to various fuel cells. However, these appear in specific fuels and are considered beyond the scope of this general review. Examples of these are halides, hydrogen chloride, and ammonia. Finally, fuel cell power unit size is a characteristic that impacts fuel processor selection. 

The application of gold as an electrocatalytic component within the fuel cell itself has to date been limited primarily to the historical use of a gold-platinum electrocatalyst for oxygen reduction in the Space Shuttle/Orbiter alkaline fuel cells (AFC)88 and the recent use of gold for borohydride oxidation in the direct borohydride alkaline fuel cell (DBAFC).89,90 Electrocatalysts with lower cost, improved carbon monoxide tolerance and higher... 

One of the drawbacks of the DMFC is that the low-temperature oxidation of methanol to hydrogen ions and carbon dioxide requires a more active catalyst, which typically means that a larger quantity of expensive platinum catalyst is required than in conventional PEMFCs. In addition, the anode has a limited carbon monoxide tolerance. Further, the overall effrdency is smaller than for a PEMFC. 

Poly(2,2 -( 1,4-phenylene)5,5 -bibenzimidazole) can be obtained under certain conditions of polymerization as a high-molecular-weight species [29]. The polymer solutions can be used directly for phosphoric acid doped PBI membranes. Such membranes show high phosphoric acid doping levels. At 160 °C a high carbon monoxide tolerance for fuel cells is observed. 

Tran PD, Le Goff A, Heidkamp J, Jousselme B, Guillet N, Palacin S, Dau H, Fontecave M, Artero V (2011) Noncovalent modification of carbon nanotubes with pyrene-functionalized nickel complexes carbon monoxide tolerant catalysts for hydrogen evolution and uptake. Angew Chem Int Ed 50(6) 1371-1374. doi 10.1002/anie.201005427... 

Shen GJ, Shieh JS, Grethlein AJ, Jain MK, Zeikus JG. (1999). Biochemical basis for carbon monoxide tolerance and butanol production by Butyribacterium methylotrophicum. Appl Microbiol Biotechnol, 51, 827-32. 

Over the past decade, proton exchange membranes for fuel cells (PEMFCs) have undergone significant development. It has been demonstrated that the overall system size can be reduced and carbon monoxide tolerance can be increased by operating the fuel cell stack at much higher temperatures than 1(X) °C and even as high as 180 °C. However, the loss of water from a Nafion-type membrane at higher temperatures (>100 °C) results in a rapid loss of conductivity [92,93]. Thus, the development of a suitable alternate water-based proton... 

Carbon Monoxide Tolerance. The interaction between CO and anode electrocatalyst is of critical importance for the performance of low temperature fuel cells because CO is common impurity in H2 and alcohol fuels decompose through a surface CO intermediate. Platinum chemisorbs CO strongly and gets poisoned easily during the fuel cell operation. 

Kwon K, Yoo DY, Park JO (2008) Experimental factors that influence carbon monoxide tolerance of high-temperature proton-exchange membrane fuel cells. J Power Sources 185(l) 202-206... 

Cutillo et al. also analysed the effect of introducing a carbon monoxide tolerant fuel cell into the system, which would make the overall system less complex [443]. Because such fuel cells were expected to be less efficient, about 3% lower efficiency was assumed. Another potential simplification was the removal of one of the water-gas shift reactors. The two stage water-gas shift reactors could be replaced by a medium temperature water-gas shift reactor with higher carbon monoxide outlet concentration in combination with the high carbon monoxide tolerant fuel cell. Alternatively, a water-gas shift reactor with heat-exchange capabilities, as discussed in Section 5.2.1, could be placed into such a system and combined with preferential oxidation and low temperature PEM fuel cell technology. 

This would increase the carbon monoxide tolerance, potentially simplifying the fuel processor design, and simplify the heat rejection. 

Figure 3.4. CO coverage on various surfaces of alloy electrodes, under steady H2 oxidation conditions at 20 mV vs. RHE in 0.1 M HCIO4 saturated with 100 ppm CO/H2 at room temperature [69]. (Reproduced by permission of ECS—The Electrochemical Society, from Holleck GL, Pasquarello DM, Clauson SL. Carbon monoxide tolerant anodes for proton exchange membrane fuel cells.)...

HoUeck GL, PasquareUo DM, Clauson SL. Carbon monoxide tolerant anodes for proton exchange membrane fuel cells. Electrochem Soc Proceedings 1999 98(27) 150-162. 

Adzic RR, Brankovic SR, Wang JX. Carbon monoxide tolerant electrooatalyst with low platinum loading and a proces for its preparation United State patent pending, 2001. 

The operation of PEM at temperature higher 100 °C is receiving much attention because it could enhance reaction kinetics at both electrodes, improve the carbon monoxide tolerance of the platinum catalyst at the anode, and simplify heat and water managements of the fuel cells. 

---