Catalyst direct methanol fuel cells

Fuel cells can run on fuels other than hydrogen. In the direct methanol fuel cell (DMFC), a dilute methanol solution ( 3%) is fed directly into the anode, and a multistep process causes the liberation of protons and electrons together with conversion to water and carbon dioxide. Because no fuel processor is required, the system is conceptually vei"y attractive. However, the multistep process is understandably less rapid than the simpler hydrogen reaction, and this causes the direct methanol fuel cell stack to produce less power and to need more catalyst. 

Lasch K, Hayn G, Jdrissen L, Garche J, Besenhardt O (2002) Mixed conducting catalyst support materials for the direct methanol fuel cell. J Power Sources 105 305-310... 

Neergat N, Sbukla AK, Gandhi KS. 2001. Platinum-based alloys as oxygen-reduction catalysts for solid-polymer-electrolyte direct methanol fuel cells. J Appl Electrochem 31 373-378. 

Dinh FIN, Ren X, Garzon FTF, Zelenay P, Gottesfeld S. 2000. Electrocatalysis in direct methanol fuel cells in-situ probing of FTRu anode catalyst surfaces. J Electroanal Chem 491 ... 

The Pt/Ru catalyst is the material of choice for the direct methanol fuel cell (DMFC) (and hydrogen reformate) fuel cell anodes, and its catalytic function needs to be completely understood. In the hrst approximation, as is now widely acknowledged, methanol decomposes on Pt sites of the Pt/Ru surface, producing chemisorbed CO that is transferred via surface motions to the active Pt/Ru sites to become oxidized to CO2... 

Seiler T, Savinova ER, Eriedrich KA, Slimming U. 2004. Poisoning of PtRu/C catalysts in the anode of a direct methanol fuel cell A OEMS study. Electrochim Acta 49 3927-3936. 

The same group, in a previous work, reported on the realization of a hybrid anode electrode [197]. An appreciable improvement in methanol oxidation activity was observed at the anode in direct methanol fuel cells containing Pt-Ru and Ti02 particles. Such an improvement was ascribed to a synergic effect of the two components (photocatalyst and metal catalyst). A similar behavior was also reported for a Pt-Ti02-based electrode [198]. Another recent study involved the electrolysis of aqueous solutions of alcohols performed on a Ti02 nanotube-based anode under solar irradiation [199]. 

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... 

Wang et al240 reported the electrooxidation of MeOH in H2S04 solution using Pd well-dispersed on Ti nanotubes. A similar reaction was studied by Schmuki et al.232 (see above), but using Pt/Ru supported on titania nanotube which appear a preferable catalyst. Only indirect tests (cyclic voltammetry) have been reported and therefore it is difficult to understand the real applicability to direct methanol fuel cell, because several other aspects (three phase boundary to methanol diffusivity, etc.) determines the performance. 

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],... 

Thomas, X., Ren, S., and Gottesfeld, J., Influence of ionomer content in catalyst layers on direct methanol fuel cell performance, Electrochem. Soc., 146, 4354, 1999. 

Steigerwalt, S.E. et al., A Pt-Ru/graphitic carbon nanofiber nanocomposite exhibiting high relative performance as a direct-methanol fuel cell anode catalyst, J. Phys. Chem. B., 105, 8097, 2001. 

Mu, Y., et al., Controllable Ptnanoparticle deposition on carbon nanotubes as an anode catalyst for direct methanol fuel cells. The Journal of Physical Chemistry B, 2005.109(47) ... 

R. X. Liu, and E. S. Smotkin, Array membrane electrode assemblies for high throughput screening of direct methanol fuel cell anode catalysts, J. Electroanal. Chem. 535, 49-55 (2002). 

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. 

In electrochemical systems, metal meshes have been widely used as the backing layers for catalyst layers (or electrodes) [26-29] and as separators [30]. In fuel cells where an aqueous electrolyte is employed, metal screens or sheets have been used as the diffusion layers with catalyst layers coated on them [31]. In direct liquid fuel cells, such as the direct methanol fuel cell (DMFC), there has been research with metal meshes as DLs in order to replace the typical CFPs and CCs because they are considered unsuitable for the transport and release of carbon dioxide gas from the anode side of the cell [32]. 

Cao, D., Bergens, S.H. 2004. Pt-Ru j , nanoparticles as anode catalysts for direct methanol fuel cells. J Power Sources 134 170-180. 

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. ... 

The purpose of the present review is to summarize the current status of fundamental models for fuel cell engineering and indicate where this burgeoning field is heading. By choice, this review is limited to hydrogen/air polymer electrolyte fuel cells (PEFCs), direct methanol fuel cells (DMFCs), and solid oxide fuel cells (SOFCs). Also, the review does not include microscopic, first-principle modeling of fuel cell materials, such as proton conducting membranes and catalyst surfaces. For good overviews of the latter fields, the reader can turn to Kreuer, Paddison, and Koper, for example. 

There is increased interest in the use of Ru-based systems as catalysts for oxygen reduction in acidic media, because these systems have potential applications in practicable direct methanol fuel cell systems. The thermolysis of Ru3(CO)i2 has been studied to tailor the preparation of such materials [123-125]. The decarbon-ylation of carbon-supported catalysts prepared from Ru3(CO)i2 and W(CO)6, Mo(CO)is or Rh(CO)is in the presence of selenium has allowed the preparation of catalysts with enhanced activity towards oxygen reduction, when compared with the monometallic ruthenium-based catalyst [126],... 

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