Active Form of Ru for the CH[sub 3]OH Electro-oxidation Reaction

Abstract

In this work, unsupported Pt∕Ru catalysts are used to address the issue of Ru oxide involvement during the methanol oxidation reaction, from the point of view of both Ru “oxidation state” (metal vs oxide) and amount of Ru oxide. It is shown that a simple electrochemical method is useful as in situ probe for the Ru oxidation state. The method also yields insight into the Pt to Ru site distribution of the catalyst surface. The results indicate that the electrochemical formation of reversibly reducible Ru oxides is effectively suppressed in CnormalH3OH solutions, most probably because of its involvement in the anodic oxidation reaction to CnormalO2 . In the case of PtRu alloys that consist of surfaces of well-distributed Pt to Ru sites, Ru oxides are not detected on this surface for CnormalH3OH concentrations greater than 0.1M . It is also shown that the electrochemical formation of Ru oxides at the potential of interest prior to the CnormalH3OH oxidation reaction deenhances the catalyst activity for CnormalH3OH oxidation. However, the experiments suggest the deenhancement is low ( <5% at 0.6 and <15% at 0.8V vs the reversible hydrogen electrode) and only observed at potentials equal to or more positive than 0.6V .

Anode Catalysts for Direct Methanol Fuel Cells in Acidic Media: Do We Have Any Alternative for Pt or Pt–Ru?

“…Dinh et al concluded that the catalytic activity for methanol oxidation was adversely affected because of blockage of active metal sites by such oxide materials. 141 Using a simple in situ electrochemical method, Bock et al found that formation of ruthenium oxides during methanol oxidation is insignificant and very little or no supportable ruthenium oxide appeared at methanol concentrations larger than 0.1 M. 210 Furthermore, they found that RuO 2 formed at a potential larger than 0.6 V inhibited methanol oxidation and that metallic Ru is the active state in the Pt−Ru catalyst to form −OH species for complete oxidation of methanol to CO 2 . Kim et al previously summarized these results and studied Ru-decorated Pt (111) substrates for methanol oxidation by XPS.…”

Nanostructured electrocatalyst for fuel cells : silica templated synthesis of Pt/C composites.

“…The XPS spectra show the order of metallic Ru for the three samples is Aerosol Pt-Ru > commercial Pt-Ru black > commercial 80% Pt-Ru/C. Although there are few studies on the most active form of Ru for methanol oxidation by Pt-Ru alloys, studies on model single-crystal Pt-Ru surfaces have indicated that the presence of Ru in metallic state is required for methanol electro-oxidation [109,110]. Some experiments have shown a decrease in methanol oxidation activity due to prior formation (i.e.…”

“…Some experiments have shown a decrease in methanol oxidation activity due to prior formation (i.e. before continuous operation) of Ru oxides is very small (<5%) and is only observable at potentials above 0.6V vs. RHE [110]. Alternative studies have shown that additional oxidation treatments in air resulted in enhanced electrochemical activity for Pt-Ru/C catalysts which was attributed to further segregation of Ru to surface and formation of RuO 2 [108].…”

Synthesis of ordered mesoporous ruthenium by lyotropic liquid crystals and its electrochemical conversion to mesoporous ruthenium oxide with high surface area

“…Takai et al have briefly reported on the synthesis of mesoporous Ru black with surface area of 62 m 2 g -1 via lyotropic crystal templating as the end member of the Pt-Ru alloy [23]. In addition to metallic Ru, high surface area ruthenium oxide is also an important material for various applications, including electrocatalysts for chlorine evolution [24], electrochemical capacitor electrodes [25][26][27][28][29], as well as fuel cell electrocatalysts [30][31][32][33][34][35][36][37][38][39]. The small particle size (1-2 nm) and the existence of appreciable pores are important requirements for the high capacitance [40][41][42].…”