Direct methanol fuel cell cathode catalyst

Despite the uncertainty regarding the exact nature of the active site for oxygen reduction, researchers have managed to produce catalysts based on heat-treated macrocycles with comparable activities to state-of-the-art platinum catalysts. In numerous cases researchers have shown activity close to or better than platinum catalysts.64,71,73,103,109 Since the active site for the ORR in these materials is not fully understood, there is still potential for breakthrough in their development. Another advantage of this class of materials that should be mentioned is their inactivity for methanol oxidation, which makes them better suited than platinum for use in direct methanol fuel cell cathodes where methanol crossover to the cathode can occur.68,102,104,122-124 While the long-term activity of heat treated materials is... 

Methanol-tolerant Catalysts for Direct Methanol Fuel Cell Cathodes... 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

Liu, R, and Wang, C. Y. Optimization of cathode catalyst layer for direct methanol fuel cells Part II Computational modeling and design. Electrochimica Acta 2006 52 1409-1416. 

Most of the catalysts employed in PEM and direct methanol fuel cells, DMFCs, are based on Pt, as discussed above. However, when used as cathode catalysts in DMFCs, Pt containing catalysts can become poisoned by methanol that crosses over from the anode. Thus, considerable effort has been invested in the search for both methanol resistant membranes and cathode catalysts that are tolerant to methanol. Two classes of catalysts have been shown to exhibit oxygen reduction catalysis and methanol resistance, ruthenium chalcogen based catalysts " " and metal macrocycle complexes, such as porphyrins or phthalocyanines. ... 

Yu, Hwan Bae Kim, Joon-Hee Lee, Ho-In Scibioh, M. Aulice Lee, Jaeyoung Han, Jonghee Yoon, Sung Pil Ha, Heung Yong. Development of nanophase Ce02-Pt/C cathode catalyst for direct methanol fuel cell. Journal of Power Sources (2005) 140(1) 59-65. 

Li, W. et al.. Carbon nanotubes as support for cathode catalyst of a direct methanol fuel cell. Carbon, 40, 791, 2002. 

This survey focuses on recent catalyst developments in phosphoric acid fuel cells (PAFC), proton exchange membrane fuel cells (PEMFC), and the previously mentioned direct methanol fuel cell (DMFC). A PAFC operating at 160-220 °C uses orthophosphoric acid as the electrolyte the anode catalyst is Pt and the cathode can... 

PEM fuel cells use a solid proton-conducting polymer as the electrolyte at 50-125 °C. The cathode catalysts are based on Pt alone, but because of the required tolerance to CO a combination of Pt and Ru is preferred for the anode [8]. For low-temperature (80 °C) polymer membrane fuel cells (PEMFC) colloidal Pt/Ru catalysts are currently under broad investigation. These have also been proposed for use in the direct methanol fuel cells (DMFC) or in PEMFC, which are fed with CO-contaminated hydrogen produced in on-board methanol reformers. The ultimate dispersion state of the metals is essential for CO-tolerant PEMFC, and truly alloyed Pt/Ru colloid particles of less than 2-nm size seem to fulfill these requirements [4a,b,d,8a,c,66j. Alternatively, bimetallic Pt/Ru PEM catalysts have been developed for the same purpose, where nonalloyed Pt nanoparticles <2nm and Ru particles <1 nm are dispersed on the carbon support [8c]. From the results it can be concluded that a Pt/Ru interface is essential for the CO tolerance of the catalyst regardless of whether the precious metals are alloyed. For the manufacture of DMFC catalysts, in... 

Electrocatalyst selection and design are the key aspects of PEM fuel cells. The most popular catalyst is platinum for the anode and the cathode in pure hydrogen cells. For direct methanol fuel cells and for hydrogen cells with carbon monoxide present, a platinum/ruthenium alloy is used. 

The held to which the specific features of CNTs and CNFs could bring the most significant advancements is perhaps that of fuel cell electrocatalysis [125,187]. The main uses of CNTs or CNFs as catalyst support for anode or cathode catalysis in direct methanol fuel cells (DMFCs) or proton-exchange membrane fuel cells (PEMFCs) are covered in Chapter 12. In this section we summarize the main advantages linked to the use of nanotubes or nauofibers for these applications. 

At present, most of the work toward building methanol fuel cells relies on technical and design principles, developed previously for polymer electrolyte membrane fuel cells. In both kinds of fuel cells, it is common to use platinum-ruthenium catalysts at the anode and a catalyst of pure platinum at the cathode. In the direct methanol fuel cells, the membrane commonly used is of the same type as in the hydrogen-oxygen fuel cells. The basic differences between these versions are discussed in Section 19.7. 

Methanol crossover, apart from the undesirable consequences mentioned above, also has some useful influence (small, to be honest) on the operation of direct methanol fuel cells. Methanol that has diffused to the cathode will be chemically oxidized by oxygen to carbon dioxide (i.e., a reaction without generating current), under the influence of the platinum catalyst. This reaction produces additional heat, and this heat may serve to accelerate the start-up of a cold fuel cell battery. 

Wen Z, Liu J, Li J (2008) Core/Shell Pt/C nanopaiticles embedded in mesoporous carbons a methanol-tolerant cathode catalyst in direct methanol fuel cells. Adv Mater 20 743-747... 

Selvarani G, Vinod Selvaganesh S, Krishnamurthy S, Kimthika GVM, Sridhar S, Pitchumani S, Shukla AK (2009) Methanol-tolerant carbon-suppOTted Pt-Au alloy cathode catalyst for direct methanol fuel cells and its evaluation by DFT. J Phys Chem C 113 7461-7468... 

Raez A, Bele P, Cremers C, Stimming U (2007) Ruthenium selenide catalysts for cathodic oxygen reduction in direct methanol fuel cells. J Appl Electrochem 37 1455-1462... 

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