Pt-alloy electrocatalysts

Igarashi H, Fujino T, Zhu Y, Uchida H, Watanabe M. 2001. CO tolerance of Pt alloy electrocatalysts for polymer electrolyte fuel cells and the detoxification mechanism. Phys Chem Chem Phys 3 306-314. 

Murthi VS, Urian RC, Mukeijee S. 2004. Oxygen reduction kinetics in low and medium temperature acid environment Correlation of water activation and surface properties in supported Pt and Pt alloy electrocatalysts. J Phys Chem B 108 11011-11023. 

Figure 30. Correlation of the oxygen reduction performance (log igoo mv) of Pt and Pt alloy electrocatalysts in a PEM fuel cell with Pt—Pt bond distance (filled circles) and the d band vacancy per atom (open circles) obtained from in situ XAS at the Pt L3 and L2 edges.(Reproduced with permission from ref 34. Copyright 1995 The Electrochemical Society, Inc.)...

More recently, Stamenkovic et al. [95,107] reported on the formation of Pt skins on Pt alloy electrocatalysts after high-temperature annealing. Pt skins were reported to exhibit strongly enhanced ORR activity. It was argued that the electronic properties of the thin Pt layer on top of the alloy alter its adsorption properties in such a way as to reduce the adsorption of OH from water and therefore to provide more surface sites for the ORR process (see Section 5.2 in Chapter 4 for a detailed discussion of skin catalysts, compare also Section 4.1.5 in the present Chapter). 

Figure 6.25. Schematic of the mechanism of the CO electrooxidation on a Pt or Pt alloy electrocatalyst.

The dependence of the Gibbs free energy pathway on electrode potential (Figure 3.3.10A) manifests itself directly in the experimental current potential characteristic illustrated in Figure 3.3.10B. At 1.23 V, no ORR current is measureable, while with decreasing electrode potentials the ORR current increases exponentially until at +0.81 V, processes other than surface kinetics (e.g. mass transport) begin to limit the overall reaction rate. Figure 3.3.10B represents a typical performance characteristic of a Pt or Pt-alloy electrocatalyst for the ORR. 

S62-163746 Takashi Itoh, Sigemilsu Matsuzawa, Katsuaki Katoh Pt Alloy Electrocatalyst and Acid Fuel Cell Electrode (Pt-Fe-Co) 13 Jan 1986 20 July 1987 Nippon Englehard... 

Mukerjee, S. In-situ x-ray absorption spectroscopy of carbon-supported Pt and Pt-alloy electrocatalysts correlation of electrocatalytic activity with particle size and alloying, Wiley VCH, 2003. 

In-Situ X-Ray Absorption Spectroscopy of Carbon-Supported Pt and Pt-Alloy Electrocatalysts Correlation of Electrocatalytic Activity with Particle Size and Alloying... 

Carbon supported Pt and Pt-alloy electrocatalysts form the cornerstone of the current state-of-the-art electrocatalysts for medium and low temperature fuel cells such as phosphoric and proton exchange membrane fuel cells (PEMECs). Electrocatalysis on these nanophase clusters are very different from bulk materials due to unique short-range atomic order and the electronic environment of these cluster interfaces. Studies of these fundamental properties, especially in the context of alloy formation and particle size are, therefore, of great interest. This chapter provides an overview of the structure and electronic nature of these supported... 

Figure 5 Comparison of oxygen reduction activity at 200mA/cm from patent literature, showing chronology of initial developments in Pt alloy electrocatalysts for PAFC s technology. Electrodes contain 0.5mg/cm Pt at 190 °C in H3PO4. KKK is Tanaka Kikinzoku Kogyo Company (K.K.K., Japan). (From Ref. 15.)...

Figure 6 Comparison of the mass activity for ORR at 0.9 V as a function of electrochemically active surface area (m /gm Pt) for supported Pt and Pt alloy electrocatalysts. (From Ref. 18.)...

Figure 7 Steady-state iR corrected Tafel plots of cathodic ORR performance of several binary Pt alloy electrocatalysts at 90 °C and 5-atm pressure. Performance for a Pt/C electrocatalyst is shown for comparison. The electrodes had 0.3mg/cm metal loading and the loading of the metal on carbon support was 20%. The humidifaction temperature for the anode and cathode gas streams were kept at 10 and 5°C above the cell temperature. 

Figure 4. Ohmic Corrected Tafel Plots for Oxygen Reduction on Pt and Pt Alloy Electrocatalysts Prepared at Northeastern (note that PtCr/C is a system being considered only for ORR fundamentals it will not be under consideration for down-selection)...

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

Bing Y, Liu H, Zhang L, Ghosh D, Zhang J (2010) Nanostrucmred Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction. Chem Soc Rev 39(6) 2184—2202... 

Much of the work done thus far has involved the use of Pt electrocatalysts and it should be clear from our discussion that surface adsorbates play crucial roles in a number of electrocatalytic reactions. Adsorbate (such as surface-oxide) effects in the traditional field of electrocatalysis in aqueous media have usually been tackled by developing Pt-alloy electrocatalysts (for the HOR, ORR, MOR, and COOR) and it will be interesting to see how ft-aUoy (as well as non-Pt) electrocatalysts perform during electrocatalysis in RTlLs. Compton has already made a step in this direction, comparing the activity of Pt electrocatalysts for the HER in RTlLs to that of other metals. In the case of the ORR in RTlLs, it will be interesting to explore whether Pt alloys are more active than Pt and whether a volcano relationship between the electrocatalyst composition and activity can be identified, as it has for the ORR in aqueous media. In addition, given that the COOR and MOR coincide with oxidation of ft surfaces, it may be natural to assume that inclusion of a readily oxidisable metal into the Pt electrocatalyst can aid in lowering the reaction overpotential but such work is yet to be done. 

Fig. 10.4 Correlation of the ORR performance of Pt and Pt-alloy electrocatalysts m PEMFC with Pt-Pt bond distance (solid circles) and the d-band vacancy of Pt (empty circles) obtained from m situ XAS (Reproduced from [52], With permission)...

Figure 16.6. Equilibrium coverage of CO on the alloy electrodes in 0.1 M HCIO4 saturated with 100 ppm balance gas. Alloy compositions are shown on the left-hand side. Potential for CO adsorption 50 mV vs. RHE, rotation rate of electrodes during the CO adsorption 1500 rpm [169]. (Igarashi H, Fujino T, Zhu Y, Uchida H, Watanabe M. CO tolerance of Pt alloy electrocatalysts for polymer electrol5de fuel cells and the detoxification mechanism. Phys Chem Chem Phys. 2001 3 306-14. Reproduced by permission of The Royal Society of Chemistry.)...

On bulk Pt-M alloys, where M is a 3d-transition metal, the specific activity for the ORR is enhanced by two to four times with respect to pure Pt [121,136-143]. Interestingly, the enhancement factor is maintained on nanometer size carbon-supported electrocatalysts [121,140,141,144-146]. Nevertheless, the long-term stability of Pt-alloy electrocatalysts remains questionable in the harsh operating conditions of a PEMFC. Dubau et al. [147-149] showed that PtsCo/C electrocatalysts suffer compositional changes at the nanoscale in real PEMFC... 

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