Reforming Tolerant

Lifetime performance degradation is a key performance parameter in a fuel cell system, but the causes of this degradation are not fully understood. The sources of voltage decay are kinetic or activation loss, ohmic or resistive loss, loss of mass transport, or loss of reformate tolerance (17). 

The definition of reformate tolerance is that, compared to running on pure H2, a fuel cell stack can run on reformate and show no change in performance, apart from that expected for dilution effects (of H2 due to CO2, N2, H2O). This requires the development of reformate-tolerant anode catalysts capable of tolerating the remaining levels of CO and CO2 in the fuel feed. 

In recent times, efforts have been made to optimize PtRu tolerance through the addition of third and fourth metals, as well as to identify alterative Pt-based catalysts with much greater reformate tolerance, particularly at much higher CO levels. Many of fhe reporfed sfudies are concerned with CO rather than reformate tolerance, and few long-ferm sfabilify measurements have been reported. 

Although great efforts have made to improved reformate-tolerant catalysts, no intrinsic reformate-tolerant catalysts have yet been discovered. The FtMo system appears to offer the greatest possibilities, especially at higher CO concentrations and at higher temperatures. However, the corrosion sensitivity of Mo over time needs to be addressed before these catalysts become practical systems. 

The central issues related to reformate tolerance as pointed out recently by us are ... 

As mentioned above, direct methanol oxidation and reformate tolerance represent two very challenging but significantly different electrocatalytic issues. This is despite the fact that poisoning by CO (or similar Ci moieties) is one of the critical aspects for both fuels. Binary catalysts such as PtSn, PtMo or PtRu offer superior performance but the precise reason for this is not known. At least 3 different mechanisms have been proposed, whereby the alloying M element ... 

Phase II Demonstration and delivery of a high efficiency reformate tolerant 7-kWf,gt fuel cell stack and power plant utilizing molded bipolar plates and natural gas fuel processor to Argonne National Laboratory for independent testing and verification. 

Built and tested reformate tolerant 60-cell 5.0-kWgjoss Teledyne Perry NG2000 stack. 

Designed and characterized reformate tolerant fuel cell on hydrogen. 

Develop anode catalyst compositions and structures with higher reformate tolerance and/or a nonprecious metal replacement for Ru, using a catalyst deposition process that easily generates new compositions and structures. 

Identified a non-precious metal replacement for Ru on the anode for reformate tolerance, which, with air bleed, gives equivalent performances within 10-20 mV. 

Men et al. reported the operation of a small-scale bread-board methanol fuel processor composed of electrically heated reactors [15]. A methanol steam reformer, two-stage preferential oxidation reactors and a catalytic afterburner were switched in series. A fuel cell equipped with a reformate-tolerant membrane, which had a 20 W nominal power output, was connected to the fuel processor and operated for about 100 h. 

Both the preferential oxidation reaction and the hydrogen oxidation taking place in parallel are highly exothermic, which can lead to local overheating of fixed catalyst beds [59]. The CO in the reformate needs to be reduced to levels below 100 ppm, which are regarded as acceptable for state-of-the-art reformate-tolerant polymer electrolyte membrane fuel cells (PEMFCs). 

Janssen GJM, de Heer MP, Papageorgopoulos DC (2004) Bilayer anodes for improved reformate tolerance of PEM fuel cells. Fuel Cells 4 169-174... 

Under reformate-feed conditions, carbon-supported PtRu alloys are widely used as reasonably reformate-tolerant anode catalysts [254-257]. However, the CO toleranee of PtRu is still unsatisfactory for the higher CO concentrations expected at system start-up or during changes in load. Moreover, the limited availabihty of... 

Cooper SJ, Gunner AG, Hoogers G, Thompsett D. Reformate tolerance in proton exchange membrane fuel cells electrocatalyst solutions. In Savadogo O, Roberge PR, editors. Proceedings of the second international symposium on new materials for fuel cell and modem battery systems 1997 July 6-10 Montreal Ecole Polytechnique de Montreal, 1997 286-96. 

Uiian, R.C., A.F. GuUa, and S. Mukerjee. 2003. Electrocatalysis of reformate tolerance in proton exchange membranes fuel cells Part I.. Electroand. Chem. 554-555 307-324. 

Urian, R. C., Gulla, A. R, and Mukerjee, S. (2003). Electrocatalysis of reformate tolerance in proton exchange membranes fuel cells Part 1.1. Electroanal. Chem. 554-555 307-324 Uribe, F. A., Valerio, J. A., Garzon, F. H., and Zawodzinski, T. A. (2004). PEMFC reconfigured anodes for enhancing CO tolerance with air bleed. Electrochem. Solid-State Letts. 7(10) A376-A379... 

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