Ternary alloy electrocatalysts

It became obvious that long-term stability of high surface area electrocatalysts was as important, or even more important than short-term activity. Luczak36 and Landsman pioneered the heat treatment of ternary alloy electrocatalysts in order to provide an ordered crystallite structure. This work was followed in Japan by Itoh and Katoh, and subsequently by... 

Synthesize binary and ternary Pt-alloy electrocatalysts by spray pyrolysis and test their performance in MEAs. 

Wang C, Li D, Chi M, Pearsmi J, Rankin RB, Greeley J, Duan Z, Wang G, van der Vliet D, More KL, Markovic NM, Stamenkovic VR (2012) Rational development of ternary alloy electrocatalysts. J Phys Chtan Lett 3(12) 1668-1673... 

The Cr(2p), Co(2p), and Ni(2p) X-ray photoelectron spectra for the samples were also studied, and the oxidation states of Cr, Co, and Ni as well as their relative intensities were obtained. From these data it was found that the Pt-Co/C sample had the lowest overall oxidizing components among the binary- and ternary-alloy electrocatalysts. Surface atomic ratios for Cr Pt, Co Pt, and Ni Pt of the carbon supported electrocatalysts, obtained from their respective X-ray photoelectron spectra, are summarized in Table 10.5. The results indicate some surface enrichment of platinum metal in all the binary-alloy electrocatalysts, namely Pt-Cr/C, Pt-Co/C, and Pt-Ni/ C. However, a surface enrichment of base metals was found in the ternary-alloy electrocatalysts, as can be seen from Table 10.5. The results suggest a higher electrocatalytic activity towards the oxygen... 

Over the past 35 years, much has been learned about the electrooxidation of methanol on the surface of noble metals and metal alloys, in particular platinum and ruthenium [2, 4, 6, 7]. Significant overpotential losses occur in the reaction due to poisoning of the alloy catalyst surface by carbon monoxide. Yet, Pt-based metal alloys are still the most popular catalyst materials in the development of new fuel cell electrocatalysts, based on the expectation that a more CO-tolerant methanol catalyst will be developed. The vast ternary composition space beyond Pt-Ru catalysts has not been adequately explored. This section demonstrates how the ternary space can be explored using the high-throughput, electrocatalyst workflow described above. 

In conclusion, the computational study of ternary Pt-Ru-X alloys suggests that future strategies toward more active electrocatalysts for the oxidation of methanol should be based on a modification of the CO adsorption energy of Pt (ligand effect), rather than on the enhancement of the oxophilic properties of alloy components (enhanced bifunctional effect). 

Fig. 11.15 Design of an electrocatalyst library of Pt-Ru-Co alloys for a more focused examination of the ternary com position space. The pie-chart character of each catalyst represents its chemical composition, with pure Pt in the upper left corner. The design was created using Library Studio [31],...

Corrosion of the material used is another factor that limits the selection of the electrocatalyst. The electrochemical corrosion of pure noble metals is not as important as in the case of binary or ternary alloys in strong acid or alkaline solutions, since these catalysts are widely used in electrochemical reactors. In the case of anodic bulk electrolysis, noble metal alloys used in electrocatalysis mainly contain noble metal oxides to make the oxidation mechanism more favorable for complete electron transfer. The corrosion problem that occurs from this type of catalyst is the auto-corrosion of the electrode surface instead of the electrode/electrolyte solution interface degradation. The problem of corrosion is considered in detail in Chapter 22. 

The project goals are to significantly improve both the kinetic performance of the electrocatalyst powder at low noble metal loading and its utilization in the cathode layers through layer structure development. Limitations in the catalyst performance will be addressed through combinatorial discovery of supported catalyst compositions and microstructures. The discovery of these new catalyst formulations will be carried out under conditions that have been scaled for commercial powder production. A large variation of binary, ternary and quaternary noble metal -transition metal alloys and mixed metal-metal oxide catalyst compositions will be screened. To improve the utilization/performance of the catalyst in MEAs,... 

Other approaches have focused upon using non-precious metals and their oxides as alternatives to the platinum catalysts. For example, the mixed oxide catalysts of the binary and ternary alloys of noble metals and transition metals have been investigated for the oxygen evolution reaction in solid polymer electrolyte water electrolyzers. Binary, ternary, and quaternary platinum alloys with base metals of Cu, Ni, and Co have been used as electrocatalysts in liquid acid electrolyte cells. It was also reported that a R-Cu-Cr alloy displayed better activity to oxygen reduction than R and Pt-Cr in liquid electrolyte.The enhanced electrocatalytic activity of these types of alloys has been attributed to various factors, including the decrease of the nearest neighbor distance of platinum,the formation of Raney type... 

Palladium is more abundant in nature and sells at half the current market price of platinum. Unlike Pt, the Pd-based electrocatalysts are more active towards the oxidation of a plethora of substrates in alkaline media. The high activity of Pd in alkaline media is advantageous considering that non-noble metals are sufficiently stable in alkaline for electrochemical applications. Importantly, it is believed that the integration of Pd with non-noble metals (as bimetallic or ternary catalysts) can remarkably reduce the cost of the membrane electrode assemblies (MEAs) and boost the widespread application or commercialization of DAFCs [1]. Palladium has proved to be a better catalyst for alcohol electrooxidation in alkaline electrolytes than Pt [2]. Palladium activity towards the electrooxidation of low-molecular weight alcohols can be enhanced by the presence of a second or third metal, either alloyed or in the oxide form [3]. 

In order to improve the power density of the DMFC, the main challenge is to develop more efficient electrocatalysts of methanol oxidation than Pt-Ru catalysts. Ternary alloys, such as Pt-Ru-Sn, have been investigated [10],... 

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