CO tolerant electrocatalysts

Several activities, if successful, would strongly boost the prospects for fuel ceU technology. These include the development of (/) an active electrocatalyst for the direct electrochemical oxidation of methanol (2) improved electrocatalysts for oxygen reduction and (2) a more CO-tolerant electrocatalyst for hydrogen. A comprehensive assessment of the research needs for advancing fuel ceU technologies, conducted in the 1980s, is available (22). 

Liu Z, Jackson G, Eichhom B (2010) PtSn intermetallic, core-shell and alloy nanoparticles as CO-tolerant electrocatalysts for H2 oxidation. Angew Chem Int Ed 49 3173-3176... 

An approach described most recently for maximizing CO tolerance at relatively low anode catalyst loadings involves a combination of a CO-tolerant electrocatalyst, for example, a PtRu alloy and a separate chemical oxidation catalyst layer of zero... 

Case Study 3 Surface-doped Pt/Ru/Co Carbon Based on the above-mentioned DFT calculations performed by Norskov [168] we have prepared trimetallic electrocatalysts having PtRu/C surface-doped with Co(0) in order to produce highly active but at the same time CO tolerant electrocatalysts. For example, Pt/Ru/Fe/C, Pt/Ru/Ni/C, and Pt/Ru/Co/C systems were manufactured with the metal ratios being 45 45 10 a/o and a total metal loading of 20 wt.% on Vulcan XC 72. The resulting catalysts were compared with the industrial PtsoRuso standard catalyst under identical conditions. Full characterization was done via a combination of TEM, XRD, XPS, andXAS measurements, further BET, and electrochemical tests [171]. 

It is generally considered that the use of CO tolerant electrocatalysts is the most promising way for solving the CO poisoning problem in PEMFCs. Since the mid-1960s, work to promote the CO tolerance has involved the modification of the catalytic platinum surface by the addition of a second metal to platinum.It is well established that binary systems of CO tolerant electrocatalysts, with Pt as one of the components, can exhibit a substantial resistance to the presence of CO in the fuel stream. It has been found that the use of a second element with Pt, such as Ru, Sn, Co, Ta, Fe, Ni, Au, Mo, W, Ti, etc., in the form of an alloy or a co-deposit yields significant improvement in the CO tolerance behaviour, relative to pure Pt. " ... 

An efficient ethanol electrooxidation catalyst should combine at least two features (i) high tolerance to CO and other intermediate species generated over the surface of the electrocatalyst during alcohol electrooxidation and (ii) ability to break the C-C bond of the ethanol molecule under mild conditions. The most relevant features for the designing of CO tolerant electrocatalysts have been described above namely, Pt modification with more oxophilic metals such as Ru, Mo or Sn renders the best electrocatalysts. This is because such oxophilic atoms promote the formation of -OfT. species (involved in the CO j oxidation reaction) at potentials that are more negative than that on pure Pt (Eq. 9.17). Among those, Sn-modified Pt electrocatalysts are the most active formulations. There is also widespread consensus that the PtsSn phase is the most active one in the CO reaction and early stages of the ethanol electrooxidation process. ... 

Brankovic SR, Wang JX, Adzic RR (2002) The CO tolerant electrocatalyst with low platinum loading and a process for its application. US Patent 132154... 

Iwase M, Kawatsu S. Optimized CO tolerant electrocatalysts for polymer electrolyte fuel cells. In Proton conducting membrane fuel cells I. Gottesfeld S, Halpert G, Landgrebe A, editors. Electrochemical Society Proceedings 1995 95-23 12-23. 

Liang Y, Zhang H, Tian Z, Zhu X, Wang X, Yi B. Synthesis and structure-activity relationship exploration of carbon-supported PtRuNi nanocomposite as a CO-tolerant electrocatalyst for proton exchange membrane fuel cells. J Phys Chem B 2006 110(15) 7828-34. 

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 ... 

Wee J.-H., K. Y. Lee, Overview of the development of CO-tolerant electrocatalysts for proton-exchange membrane fuel cells, J. Power Sources, 157, 128 (2006). 

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