Platinum monolayer catalyst

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. 

A new method of synthesis of selective platinum catalysts for the hydrogenation of unsaturated carbonyl compounds is presented. Platinum was deposited on the supports tailored with the monolayer of transition metal oxide. Selectivity of these catalysts strongly depended on the type of inorganic support as well as on the type of transition metal in the monolayer. Catalysts were tested in the hydrogenation of furfural, crotonaldehyde and cinnamaldehyde. Selectivity of the synthesis of the appropriate unsaturated alcohols was enhanced when compared with the reactions performed over classical Pt-metal oxide catalysts. 

Galvanic displacement method is also often used for synthesizing catalysts. By this method, low Pt-content electrocatalysts can be obtained. For example, a carbon-supported core—shell structured electrocatalyst with bimetallic IrNi as the core and platinum monolayer as the shell has been successfully synthesized using this method. In this synthesis, IrNi core supported on carbon was first synthesized by a chemical reduction and thermal annealing method and a Ni core and Ir shell structure could be formed finally. The other advantage of this method is that the Ni can be completely encased by Ir shell, which will protect Ni dissolve in acid medium. Secondly, IrNi PtML/C core—shell electrocatalyst was prepared by depositing a Pt monolayer on the IrNi substrate by galvanic displacement of a Cu monolayer formed by under potential deposition (UPD). 

Vukmirovic MB, Bliznakov ST, Sasaki K, Wang JX, Adzic RR (2011) Electrodeposition of metals in catalyst synthesis the case of platinum monolayer electrocatalysts. Electrochem Soc Interface 20(2) 33 0... 

Zhang et al. investigated Pt monolayer deposits on Pd(lll) single crystals (Pt/Pd(lll)) and on Pd/C nanoparticles (Pt/Pd/C) for ORR [18]. The ORR reaction mechanism of the mono-layer catalysts was found to be the same as that on pure Pt surface. Pt/Pd(lll) was found to have a 20 mV improvement in half-wave potential versus Pt(lll), and the Pt/Pd/C had a Pt-mass activity 5-8 times higher than that of Pt/C catalyst. The enhanced ORR activity is attributed to the inhibited OH formation at high potential, as evidenced from XAS measurements. In a real fuel cell test, 0.47gpt/kW was demonstrated at 0.602 V [21]. In a related study, the ORR on platinum monolayers supported on Au(lll),... 

A full carbon monolayer is permeable to reactants and products of surface reactions, as significant quantities of H, CO, and HCOOH adsorb or react through the adlayer. One consequence of this finding for applied electrocatalysis is that a typical platinum particle catalyst on a carbon support may maintain activity in the event that the particle becomes fully covered with carbon. This effect will thus help in interpreting the behavior of aged or sintered catalysts. 

Zhang J, Vukmirovic MB, Sasaki K, Uribe F, Adzic RR (2005) Platinum monolayer electro catalysts for oxygen reduction effect of substrates, and long-term stability. J Stab Chem Soc 70(3) 513-525... 

The stability of platinum monolayer electrocatalysts under conditions of potential cycling is higher than that of intrinsic platinum surfaces. We ascribed this advantage to a shift in the surface oxidation (PtOH formation) of monolayer catalysts to more positive potential than those for Pt/C. The shift is occasioned by the electronic effect of the underlying substrates, as discussed next. 

Zhang, J., Lima, F. H. B., Shao, M. H., SasaM, K., Wang, J. X., Hanson, J. and Adzic, R. R. (2005b) Platinum monolayer on nonnoble metal-noble metal core-shell nanoparticle electro-catalysts for Oj reduction, J. Phys. Chem. B 109, 22701-22704. 

Andreaus B, Maillard F, Kocylo J, Savinova ER, Eikerling M. 2006. Kinetic modeling of CO monolayer oxidation on carbon-supported platinum catalyst nanoparticles. J Phys Chem B 110 21028-21040. 

Catalyst samples were pressed as a wafer in the stainless steel or perspex sample holder. It was calculated that, due to diffusion limitations, the aqueous samples needed at least 6 hours pretreatment in order to attain monolayer coverage of the platinum with oxygen or hydrogen throughout the sample. A pretreatment time of 20 hours was chosen. 

In this paper we report the application of bimetallic catalysts which were prepared by consecutive reduction of a submonolayer of bismuth promoter onto the surface of platinum. The technique of modifying metal surfaces at controlled electrode potential with a monolayer or sub-monolayer of foreign metal ("underpotential" deposition) is widely used in electrocatalysis (77,72). Here we apply the theory of underpotential metal deposition without the use of a potentiostat. The catalyst potential during promotion was controlled by proper selection of the reducing agent (hydrogen), pH and metal ion concentration. 

Fig. 28. Schematic representation of a platinum catalyst with a monolayer of carbonaceous overlayer showing the exposed platinum clusters.

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