Alloy electrocatalysts, for

Table 3.1 lists some of the anodic reactions which have been studied so far in small cogenerative solid oxide fuel cells. A more detailed recent review has been written by Stoukides46 One simple and interesting rule which has emerged from these studies is that the selection of the anodic electrocatalyst for a selective electrocatalytic oxidation can be based on the heterogeneous catalytic literature for the corresponding selective catalytic oxidation. Thus the selectivity of Pt and Pt-Rh alloy electrocatalysts for the anodic NH3 oxidation to NO turns out to be comparable (>95%) with the... 

Quantitative analysis can be carried out by chromatography (in gas or liquid phase) during prolonged electrolysis of methanol. The main product is carbon dioxide,which is the only desirable oxidation product in the DMFC. However, small amounts of formic acid and formaldehyde have been detected, mainly on pure platinum electrodes. The concentrations of partially oxidized products can be lowered by using platinum-based alloy electrocatalysts for instance, the concentration of carbon dioxide increases significantly with R-Ru and Pt-Ru-Sn electrodes, which thus shows a more complete reaction with 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. 

Shao MH, Huang T, Liu P, Zhang J, Sasaki K, Vukmirovic MB, Adzic RR. 2006a. Palladium monolayer and palladium alloy electrocatalysts for oxygen reduction. Langmuir 22 10409-10415. 

Yang H, Alonso-Vante N, Leger JM, Lamy C. 2004. Tailoring, structure, and activity of carbon-supported nanosized Pt-Cr alloy electrocatalysts for oxygen reduction in pure and methanol-containing electrolytes. J Phys Chem 108 1938-1947. 

Sun YP, Buck H, Mallouk TE. 2001. Combinatorial discovery of alloy electrocatalysts for amperometric glucose sensors. Anal Chem 73 1599-1604. 

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. 

Previously, the first reviews on alloy electrocatalysts for oxygen reduction in phosphoric acid fuel-cells44"46 concentrated on those patents that had been issued in the United States, since that was where most of the early work had been done. Subsequendy, similar alloy work has been done in Japan, and that work is reflected in the Japanese patent literature shown in Table 3, whence corresponding alloy-combination atom ratios and the air/oxygen performance values are given in Table 3a. 

IX. DEVELOPMENT OF ALLOY ELECTROCATALYSTS FOR HYDROGEN MOLECULE OXIDATION... 

III. CASE STUDY Pt-Co ALLOY ELECTROCATALYSTS FOR OXYGEN REDUCTION... 

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.)...

In addition to having a good CO tolerance, Pt-Ru electrocatalysts must also have a high activity for H2 oxidation. Comparison of the mass-specific activity of a PtRu2o electrocatalyst with a commercial Pt-Ru 1 1 alloy electrocatalyst for the oxidation of pure H2 showed that its activity is tluee times that of the commercial alloy. This indicates that even for a low Pt coverage on Ru, its activity for H2 oxidation is preserved, a prerequisite for an active CO tolerant catalyst. Comparing the CO tolerance of the PtRu2o electrocatalyst with that of two commercial Pt-Ru alloy electrocatalysts for the oxidation of 1095 ppm CO in H2 confirmed the exceptional stability of the former (Fig. 20) the measurements... 

Wang C, Markovic NM, Stamenkovic VR. Advanced platinum alloy electrocatalysts for the oxygen reduction reaction. ACS Catal 2012 2(5) 891-8. 

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... 

Shao M, Liu P, Zhang J, Adzic RR (2007) Origin of enhanced activity in palladium alloy electrocatalysts for oxygtai reduction reaction. J Phys Chem Bill 6772-6775... 

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. 

Antolini E, Salgado IRC, Gonzalez ER (2006) The methanol oxidation reaction on platinum alloys with the first row transition metals the case of Pt-Co and -Ni alloy electrocatalysts for DMFCs a short review. Appl Catal Environ 63 137-149... 

Camara GA et al (2002) Correlation of electrochemical and physical properties of PtRu alloy electrocatalysts for PEM fuel cells. J Electroanal Chem 537(l-2) 21-29... 

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.)...

Stonehart, P. (1992) Development of alloy electrocatalysts for phosphoric add fuel cells (PAFC). Journal of Applied Electrochemistry 22, 995-1001. 

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