Platinum alloy catalyst

The operating temperature is within the range 50-140 °C (depending on the stability of the electrolyte) and the electrodes consist on dispersions of - platinum or platinum alloys catalysts on porous carbon paper. 

H4-135642 Paul Stonehart, Kazunori Tsurumi, Tosbihide Nakamura, Akira Sato Platinum Alloy Catalyst and Process for Preparing (Pt-Ni-Co-Mn) 26 Sept 1990 11 May 1992 Tanaka Kikinzoku Kogyo Stonehart Associates... 

Figure 7. Platinum, platinum alloy, and ordered platinum alloy catalyst mass oxygen reduction activities at 0.9 V. 0.75 mg Platinum loading on the electrode. Influence of temperature.

There has been a number of studies of carbon-supported platinum and platinum-alloy catalysts. INS has been used in the characterisation of activated catalyst supports from different natural sources through patterns of edge termination reflected in the INS spectra in the out-ofplane C-H bending region near 880 cm [54,55]. 

Another system, where catalytic active oxide particles might lead to a new development, is the polymer electrolyte membrane fuel cell (PEMFC). This t5rpe of fuel cell preferentially works with platinum and platinum alloy catalysts. The development of an effective oxide catalyst could solve some of the problems connected with the application of these systems. 

Platinum-alloy catalysts in particular platinum-ruthenium alloys are also capable to mitigate the CO poisoning effect [41]. However, only moderately higher CO concentrations can be tolerated while the stability of the catalyst is questionable due to mthenium dissolution. 

Platinum alloy catalysts have been found to improve the oxygen reduction kinetics. Shrinking of the Pt-Pt distance as well as electronic effects have been used to explain this phenomenon. Alloying of platinum with non noble metals such as cobalt, nickel or iron after extended contact with acid electrolytes left platinum rich skins on the surface, still providing improved kinetics. Pathways of the nrai... 

It has been observed that with time, the performance enhancement of platinum alloy catalysts will be lost and the catalysts activity becomes more and more comparable to pure platinum catalysts. Thermal treatment of the catalysts or catalyst supports can significantly influence catalyst performance and endurance [50]. 

Gurau B, Viswanathan R, Liu R, Lafrenz TJ, Ley KL, Smotkin ES, Reddington E, Sapienza A, Chan BC, Mallouk TE, Sarangapani S (1998) Structural and electrochemical characterization of binary, ternary, and quaternary platinum alloy catalysts Jot methanol electro-oxidation. J Phys Chem B 102 9997-10003... 

This selected brief review will be focused on the research and development progress on ORR kinetics. The origin of the problem related with the low ORR activity of platinum will be discussed, followed by a review of recent progress in making more active, more durable platinum-based ORR catalysts. These include platinum alloy catalysts, platinum monolayer catalysts, platinum nanowire and nanotube catalysts, and the more recent shape- and facet-controlled platinum-alloy nanocrystal catalysts. The progress in the mechanistic understanding on the correlation between the activity and the electronic and structural properties of surface platinum atoms will be reviewed as well. The future direction of the research on platinum-based catalysts for PEM fuel cell apphcation will be proposed. 

Kocha SS, Gasteiger HA (2004) Platinum alloy catalysts for PEMFCs. Htany B. Gonzalez Convention Center, San Antonio, TX. http //www.fijelcellst3niiiar.e(Hn ast-eonferences/ 2004.aspx... 

Wei ZD, Guo HT, Tang ZY. Heat treatment of carbon-based powders carrying platinum alloy catalysts for oxygen reduction influence on corrosion resistance and particle size. J Power Sources 1996 62 233-6. 

Catalytic activity is closely dependent on the method of preparation, so considerable attention has been focused upon new preparation methods to improve the performance of carbon-supported platinum alloy catalysts in DMFC applications. The simultaneous reduction of metal salts [86-88], microwave-assisted reactions [89, 90], micro-emulsion-based synthesis [91-93], and the reduction of single-source molecular precursors [94-99] have been used to various extents. 

Platinum Alloy Catalysts for Direct Methanol Fuel Cell Anodes... 

With respect to the positive effects of Pt alloying, some improvement in catalyst stability and fuel cell durability have also been observed. Several studies [1, 27-29] have demonstrated that alloy particles have better resistance to sintering than pure platinum particles. The sintering effect may be attributed to base metals hindering Pt mobility on carbon, as well as Pt alloy particles usually being larger than Pt alone. Yu et al. [30] found that some platinum alloy catalysts, particularly... 

Stonehart, P. 1997. Platinum alloy catalyst. Patent US5593934. 

Carbon corrosion and platinum dissolution in the acidic electrolyte at elevated temperatures are well recognized from the early years of research on PAFCs and are definitely relevant to HT-PEMFCs based on the acid-doped FBI membranes. Both mechanisms are enhanced at higher temperatures and higher electrode potentials. This should be taken into account when platinum alloy catalysts are considered for the HT-PEMFC. More efforts are also needed to develop resistant support materials based on either structured carbons or non-carbon alternatives. 

As mentioned earher, since the platinum (and other precious metals) loading reduction cannot overcome the price increment, the development of a nonprecious catalyst is perhaps the most feasible solution for PEM fuel cell commercialization. The nonprecious catalysts generally include carbides, nitrides, oxides, carbonitrides, oxynitrides, materials derived from macrocycles and porphyrins, and composites of these materials (Borup et al., 2007). However, unlike the platinum alloy catalysts that have already shown both the improved reaction activity and stability, none of the nonprecious catalysts demonstrated both good reaction activity and stability to the best of the authors knowledge. Some nonprecious catalysts have reasonable reaction activity but poor stability (e.g., some transition metal carbides), and... 

Research activity in this field has been quite important and is continuing. Thus, the effect of alloys deposited on a support by chemical vapor deposition (Seo et al., 2006b) and by dual ion-beam-assisted deposition (IBAD Gulla et al., 2006) has been studied. Another advantage of such platinum-alloy catalysts that was noted by many workers is their reduced sensitivity to methanol crossing over to the oxygen electrode in DMFCs and the associated improvement in the stability of the electrode s potential (Yuan et al., 2006 Baglio et al., 2007). 

Anodes are usually very similar to, if not identical to those that serve as cathodes. Anodes that operate on reformed-hydrocarbon fuels, which contain some carbon monoxide, generally utilize a platinum-alloy catalyst to enhance co-tolerance. The catalyst-layer structure is sometimes altered between anodes and cathodes to adjust their respective hydrophobicity and reactant-diffusion properties. The thickness of the catalyst layer typically ranges from 10 to 20 tm, that of the substrate from 0.1 To 0.5 mm (uncompressed). 

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