Activity and Durability of Ternary PtRuIr∕C for Methanol Electro-oxidation

Abstract

Carbon supported Pt 1 Ru 1 Ir x ͑0 ഛ x ഛ 2͒ nanoparticles were prepared by a coimpregnation reductive pyrolysis method and their electrocatalytic activity toward methanol electro-oxidation at 25, 40, and 60°C was investigated. The mass activity ͑current normalized by the mass of Pt͒ for methanol electro-oxidation increased as a function of Ir content and cell temperature. Despite the increase in methanol electro-oxidation activity, the addition of Ir does not affect the CO tolerance of the ternary electrocatalyst. The addition of Ir also enhances the durability of the catalyst. The enhancement in activity and durability is discussed based on CO stripping measurements and X-ray photoelectron spectroscopy analysis of the catalysts. The direct methanol fuel cell is widely considered as a potential highly efficient and clean energy source. Despite considerable advances in recent years, many technical barriers still need to be overcome in the development of electrocatalysts for the widespread commercialization.1 One of the major problems is the insufficient catalytic activity of the anode catalysts leading to slow kinetics of methanol electro-oxidation. The binary PtRu alloy is one of the most promising electrocatalysts for methanol electro-oxidation 2,3 due to the ability of Ru in the alloy to promote fast oxidation of CO. The promotional effect of Ru has mainly been discussed based on the so-called bifunctional mechanism 4 or electronic effect 5,6 or a mixture of both.7 It is generally accepted that the oxophilic ruthenium in the Pt-Ru catalyst dissociates water into OH and H at lower potential than that on platinum. 8,9 The CO chemisorbed on the platinum sites can then be oxidized by the neighboring OH. In addition, the electronic structure of platinum can be modified by forming an alloy with Ru, resulting in the weakening of CO adsorption on platinum. 10,11Despite the promising activity of the PtRu alloy, further improvement in activity and durability is necessary for practical application. The incorporation of a third metal, such as W, Mo, Co, Ni, Sn, Os, Rh, Pb, Bi, Ir, etc., 12-25 is a typical approach to develop methanol oxidizing catalysts with improved performance. Among the ternary alloy catalysts, the PtRuIr/C system seems to be promising; the promoting effect of Ir on the methanol electro-oxidation has been studied to some extent with limited composition and temperature range. [18][19][20][21][22][23][24][25] In this work, we conducted a systematic study on the PtRuIr/C system by preparing a series of catalysts with various Ir content and studied their electrocatalytic methanol oxidation activity at different temperatures. In addition to the initial quasi-steady state activity, the durability of the ternary catalyst was studied. ExperimentalCarbon-supported PtRuIr electrocatalysts were prepared by an impregnation reductive pyrolysis method similar to previously described methods. 26,27 In a typical procedure, carbon black ͑Vulcan XC-72R, 254 m 2 g −1 ͒ was added to 1-butanol solutions of H 2 PtCl 6 ·6H 2...

Iridium Application in Low‐Temperature Acidic Fuel Cells: Pt‐Free Ir‐Based Catalysts or Second/Third Promoting Metal in Pt‐Based Catalysts?

“…[77] The enhanced performance was attributed mainly to the interaction between RuO 2 and IrO 2 , leading to facile oxidation of CO ads on active metal sites at a lower potential relative to the Pt-Ru/C analogue. As can be seen in Figure 5, independent of the data set of ternary Pt-Ru-Ir catalysts (Ru:Ir atomic ratio constant, different Pt content, [78] or Pt:Ru atomic ratio constant, different Ir content [79] ), the steady-state current per unit Pt mass by CA measurements at room temperature almost linearly increases with increasing Ir content in the catalyst. [78][79][80][81][82] In all cases, the addition of Ir to benchmark Pt-Ru increases its MOR activity.…”

“…[78][79][80][81][82] In all cases, the addition of Ir to benchmark Pt-Ru increases its MOR activity. As can be seen in Figure 5, independent of the data set of ternary Pt-Ru-Ir catalysts (Ru:Ir atomic ratio constant, different Pt content, [78] or Pt:Ru atomic ratio constant, different Ir content [79] ), the steady-state current per unit Pt mass by CA measurements at room temperature almost linearly increases with increasing Ir content in the catalyst. As the particle size [78] or the ECSA [79] are independent of Ir content, the positive effect of Ir is not due to an increase of surface area.…”

“…On this basis, ternary Pt-Ru-Ir catalysts have been tested for methanol oxidation. As the particle size [78] or the ECSA [79] are independent of Ir content, the positive effect of Ir is not due to an increase of surface area. As can be seen in Figure 5, independent of the data set of ternary Pt-Ru-Ir catalysts (Ru:Ir atomic ratio constant, different Pt content, [78] or Pt:Ru atomic ratio constant, different Ir content [79] ), the steady-state current per unit Pt mass by CA measurements at room temperature almost linearly increases with increasing Ir content in the catalyst.…”

NANOPARTÍCULAS CASCA-NÚCLEO E LIGA DE PtPb/C: ESTUDO COMPARATIVO DA ATIVIDADE ELETROCATALÍTICA PARA REAÇÃO DE OXIDAÇÃO DE ETANOL

“…Na maioria dos casos, a Pt é utilizada sob a forma de pequenas NP, com o objetivo de maximizar a utilização do metal, resultando em área de superfície elevada, que é especialmente essencial para aplicações na catálise (Koh et al, 2007). Outra forma eficaz de reduzir o uso da Pt é fazer ligas com um segundo ou terceiro metal, o que é uma forma conveniente para modificar as propriedades eletrocatalíticas da platina, a fim de superar o envenenamento e a diminuição do seu uso (Geng et al, 2009). Uma segunda opção, seria combinar Pt com uma base de metal, o que cria uma estrutura de nanopartículas de catalisadores com um núcleo de metal base e casca de Pt (Kristian e .…”

The Effect of PtRuIr Nanoparticle Crystallinity in Electrocatalytic Methanol Oxidation

“…[7,8,9,10]. Among these ternary alloy catalysts, the PtRuIr/C system seems particularly promising [11,12,13]. Furthermore, the effect of composition for PtRuIr/C catalyst was systematically studied.…”