PtRu/C catalysts

Seiler T, Savinova ER, Eriedrich KA, Slimming U. 2004. Poisoning of PtRu/C catalysts in the anode of a direct methanol fuel cell A OEMS study. Electrochim Acta 49 3927-3936. 

The analysis of the EXAFS of alloy catalyst particles is inherently more complicated than that of single metals. In the case of PtRu catalysts there is an added complication that the backscattering from Pt and Ru neighbors at similar distances interfere with one another, giving rise to beats in the EXAFS data. This phenomenon was first described by McBreen and Mukerjee ° for a poorly alloyed 1 1 atomic ratio PtRu/C catalyst. The presence of beats in the EXAFS data is more apparent in the EXAFS obtained at the Pt L3 edge for a well mixed 1 1 PtRu/C catalyst than in that of a poorly mixed catalyst of the same composition, as shown in Figure 27 compare panels a and c. Pandya et al. showed that the beats occur because the difference in the backscattering phase shifts from Pt and Ru is... 

The applied electrode potential has been shown to have an effect on both the XANES and EXAFS of PtRu catalysts. The variations of the Pt d band vacancy per atom, (/7j)t,s, with potential over the range 0.0—0.54 V vs RHE for both the poorly mixed 1 1 PtRu/C catalyst investigated by McBreen and Mukerjee ° and a well mixed 1 1 PtRu/C catalyst studied by Russell et al. were less than that for a pure Pt/C catalyst. McBreen and Mukerjee attributed this difference to a reduction in the adsorption of hydrogen on the Pt sites of the alloy catalyst. The results also provide evidence of an electronic effect upon alloying Pt with Ru. The effects on the Ru XANES were much less significant, but some evidence of a change to a higher oxidation state at potentials above 0.8 V was observed. ... 

The influence of the applied potential on the XAS of PtRu fuel cell catalysts is also apparent in data collected under fuel cell conditions. Viswanathan et al. reported XANES data obtained at both the Pt L3 and Ru K edges for a 1 1 PtRu/C catalyst prepared as a Nafion bound MEA. They found that both the Pt and Ru were metallic in both the freshly prepared ME As and ME As under operating conditions. 

Table 9.3 gives the physicochemical characterizations of the PtRu/C catalysts obtained under different experimental conditions (nominal metal atomic ratio in solution and value of tM). 

Nano-sized PtRu catalysts supported on carbon have been synthesized from inverse micro emulsions and emulsions using H2PtClg (0.025 M)/RuCl3 (0.025 M)/NaOH (0.025 M) as the aqueous phase, cyclohexane as the oil phase, and NP-5 or NP-9) as the surfactant, in the presence of carbon black suspended in a mixture of cyclohexane and NP-5-I-NP-9 [164]. The titration of 10% HCHO aqueous solution into the inverse micro emulsions and emulsions resulted in the formation of PtRu/C catalysts with average particle sizes of about 5 nm and 20 nm respectively. The RuPt particles were identified by X-ray diffraction. X-ray photoelectron, and BET techniques. All of the catalysts prepared show characteristic diffraction peaks pertaining to the Pt fee structure. XPS analysis... 

Figure 20. Comparison of tiie coverage in species coming from the adsorption of methanol for different PtRu/C catalysts. The experiments were realized under the same experimental conditions as in Fig. 19 with coreduced Pto.8Ruo.2/C and Pto.sRuo.s/C catalysts, and a codeposited Pto.8+Ruo.2/C catalyst.

Figure 35 shows a typical set of results obtained during the electro-oxidation of ethanol on PtRu/C catalyst with the voltam-mogram (Fig.35a) and three mass spectrometric cyclic voltammo-grams (MSCVs) (Figs. 35b, 35c and 35d). 

Figure 35. Simultaneously recorded CVs (a) and MSCVs for m/z = 22 (b), m/z = 29 (c) and m/z = 15 (d) for the oxidation of ethanol on a PtRu/C catalyst in a 0.5 M H2SO4 + 0.1 M ethanol solution. Scan rate 10 mV s . Arrows indicate the direction of potential scan.

This quantitative analysis allows a comparison in the product yield, Wq, for the ethanol oxidation reaction between different catalysts. In the discussed example, the three catalysts considered present close yields, with a low CO2 production (for Pt/C and PtRu/C catalysts CO2 is only produced during the positive going scan), whereas acetaldehyde and acetic acid both present a product yield of 60-70 % and 30-40 %, respectively. A shght increase in the acetaldehyde yield can be observed for the PtRu catalyst, leading to a lower Faradic efficiency for the ethanol oxidation reaction, compared to that obtained on Pt/C and PtsSn/C catalysts. 

V vs RHE(Reversible Hydrogen Electrode)) in Pt catalysts is well defined, while for PtRu catalysts it is less defined, because the adsorption/desorption hydrogen peaks are not developed on Ru. The double layer region of the PtRu/C catalysts is larger than for Pt/C, both because of the presence of more oxygenated species and also of a larger surface area due to a smaller particle size. Furthermore, the performance of the PtRu/C catalysts, for methanol oxidation, shows a superior activity as compared to the Pt catalysts in the... 

Liu et al. have prepared PtRu/C catalysts from microemulsions and emulsions . Their results show how particles prepared from microemulsions displayed a lower particle size than the emulsion counterparts. 

Experimental Initially a PtRu/C catalyst was generated using RuCh and N(oct)4Bet3H in THF solution to form the PtRu-precursor which was supported on the Vulcan XC 72 carrier. After the conditioning step the PtRu/C material was redispersed in THF. Then, the respective amount of zerovalent Fe-, Ni-, or... 

Lizcano-Valbuena WH, Paganin VA, Gruizalez ER (2002) Methanol electro-oxidatirm on gas diffiision electrodes prepared with PtRu/C catalysts. Electrochim Acta 47 3715—3722... 

Fig. 1.6 Time dependence of the PIml/Ru electrocatalysts activity at 0.69 V with two different compositions indicated in the graph and a commercial PtRu/C catalyst for methanol oxidation [77] (reproduced with permission from J. Electrochem. Soc. 155, B185 (2008). Copyright 2003, The Electrochemical Society)...

Yang B, Lu Q, Wang Y, Zhang L, Lu J, Liu P (2003) Simple and low-cost preparation method for highly dispersed PtRu/C catalysts. Chem Mater 15 3552-3557... 

Fuel Cell Reactions. Low temperature fuel cells such as proton exchange membrane fuel cells (PEMFC) or direct methanol fuel cells (DMFC) employ large amounts of noble metals such as Pt and Ru. There has been extensive research to replace these expensive metals with more available materials. A few studies considered transition metal nitrides as a potential candidate. In an anode reaction of DMFC, Pt/TiN displayed the electroactivity for methanol oxidation (53). Pt/TiN deposited on stainless steel substrate showed the high CO tolerance in voltammogram performed with a scan rate of 20 mV/s and 0.5 M CH3OH - - 0.5 M H2SO4 electrolyte. The bifunctional effect of Pt and TiN for CO oxidation was mentioned as observed between Pt and Ru in commercial PtRu/C catalysts. 

Employing PtRu/C catalysts, Dickinson et al. confirmed at 298 K flie higher activity of the catalyst formulation richer in Pt (i.e., Pt Ru at. ratio 3 2 vs. 1 1) over the entire range of anode potential from about 0.3 to 0.8 V vs. RHE [95]. However, at higher temperatures (318 K and 338 K) there was an interaction effect between thermal activation and anode potential. At both 318 and 338 K there was virtually no significant difference between the two compositions at potentials below 0.5 V vs. RHE. Only at E > 0.5 V did the formulation richer in Ru (1 1 atomic ratio) better performance at higher temperatures. 

Xue X, Liu C, Xing W, Lu T. Physical and electrochemical characterizations of PtRu/C catalysts by spray pyrolysis for electrocataljftic oxidation of methanol. J Electrochem Soc 2006 153 E79. 

Figure 10.8 shows typical cyclic voltammograms of Pf/C and PtRu/C catalyst electrodes in 0.5 M H2SO4 solution. In the case of the Pt/C catalyst, two well-resolved peaks on the cathodic sweep at the low potentials area eorrespond to the hydrogen deposition on the electrode surface. The surfaee area ean be ealculated by the following equation [60-62] ... 

Figure 10.8. Cyclic voltammograms of Pt/C and PtRu/C catalyst electrodes in 0.5 M H2SO4...

Lu Q, Yang B, Zhuang L, Lu J. Anodic activation of PtRu/C catalysts for methanol oxidation. J Phys Chem B 2005 109 1715-22. 

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