Dependence of CH[sub 3]OH Oxidation Activity for a Wide Range of PtRu Alloys

Abstract

Unsupported PtRu alloy powders of a wide range of compositions were prepared at low temperatures by carefully adjusting the preparation procedure. PtRu alloys of essentially the same surface, nominal and bulk composition, were formed up to ca. 46 atom % Ru content. Adsorbed CO stripping voltammetry and CH 3 OH oxidation characteristics, namely, i-V curves and pseudo-steadystate current density values recorded at constant potentials, were the same as reported for corresponding bulk alloys, suggesting that the electrocatalytic activities of the powders can be compared to bulk alloys. CH 3 OH oxidation activities obtained for PtRu alloy, Pt, and Ru powders showed the PtRu alloy of 70:30 atom % Pt:Ru composition to exhibit the highest activity independent of the temperature and potential tested ͑0.3 and 0.4 V vs. a reversible hydrogen electrode͒. The experimental pseudo-steady-state current density values for the CH 3 OH oxidation reaction were found to show the same dependence on Ru content as theoretical values calculated assuming that an assembly of three neighboring Pt and one Ru site are involved in the oxidation of a CH 3 OH molecule.

Small step graphs of cell data versus composition for ccp solid-solution binary alloys: Application to the (Pt,Ir), (Pt,Re) and (Pt,Ru) systems

“…For Ru content greater than 80%, the alloys are hcp. Bock et al [3] report an ab initio low-resolution plot of the a cell edge versus Ru content, also plotting on a straight line with same slope as the experimental data. Strictly speaking, this straight line cannot be called Vegard's law because pure Ru is hcp.…”

“…We contributed before to the characterization of the slope of Vegard's law in (Pt,Ru) cell data (Bock et al [3]). Ab initio modeling of cell data for solid-solution systems is performed by optimizing cell and coordinate data for hypothetical stoichiometric compounds within the known range of the solid-solution.…”

The role of the WOxad-component to Pt and PtRu catalysts in the electrochemical CH3OH oxidation reaction

“…The Ru surface enrichment is seen to be significant, as the Ru surface atomic ratio is about 2.8 and 2.5 times higher than the bulk atomic ratio for the PtRu/C and PtRuWO x /C catalyst, respectively. This surface enrichment of Ru may be caused by differences in the reaction rates of the individual precursor salts with the NaBH 4 solution, as in fact the reduction reaction of the Pt precursor is more rapid than the reduction reaction of the Ru precursor [12]. It should be noted that the Pt:WO x ratio used here is equivalent to the ratio of the PtWO x /C catalyst reported to be most active for the CH 3 OH oxidation reaction by Shukla et al [8].…”

“…Furthermore, the XRD data suggest the average Pt particles size for the Pt/C and PtWO x /C catalysts prepared in this work to be larger than for the catalysts prepared by Shukla et al [8], who reported average Pt particle sizes of 6 and 6.7 nm for the as prepared Pt/C and PtWO x /C catalysts, respectively. These differences likely indicate some variations in the catalyst preparation procedures such as the rate of NaBH 4 addition [12] that influence particle size and surface concentrations. Figure 4(a)-(c) shows the XPS spectra for the Pt 4f, Ru 3p and W 4f core level regions collected for the PtRuWO x /C catalyst.…”

DMFC electrode preparation, performance and proton conductivity measurements

“…5MH 2 SO 4 at room temperature. A cat was obtained using the charge of CO ads (Q COads ) and a conversion factor of 420 lCc m -2 [11][12][13][14], For DMFC performance measurements, a 1 M methanol solution was pumped at 2 mL min -1 through the anode side and the cathode side was exposed to dry air at a flow rate of 200 sccm. Fresh methanol solutions were used to collect the individual DMFC performance curves.…”