Pt-Ru-Ir Nanoparticles Prepared by Vapor Deposition as a Very Efficient Anode Catalyst for Methanol Fuel Cells

Abstract

Preparation of Pt-Ru-Ir nanoparticle catalysts on carbon black by a novel vapor deposition method is reported. Particle size as assessed by transmission electron microscopy is ca. 2.5 nm with narrow distribution. Moreover, they are homogeneously dispersed on the substrate. The electrocatalytic activity of the particles toward methanol electro-oxidation was investigated by cyclic voltammetry, chronoamperometry at constant potential, and adsorbed CO-stripping voltammetry. It was found that these catalysts possess outstanding activity for methanol electro-oxidation. This is over one order of magnitude higher than in state of the art catalysts. The novel catalysts have the potential to bear significant performance improvement of direct methanol fuel cells. Fuel cells bring the promise of clean electrical energy generation with high efficiency. The polymer electrolyte fuel cell operating at relatively low temperature ͑typically from 25 to 130°C͒ with liquid methanol feed ͑direct methanol fuel cell, DMFC͒ is particularly promising for mobile applications, such as cars and mobile telephones. One major technical problem affecting up-to-date DMFCs is the low activity of the anode catalyst. Thus, in order to attain adequate power density and efficiency, a burdensome amount of catalyst is required. The latter is made out of metals such as platinum and ruthenium that are also very costly. Methanol electro-oxidation at Pt-Ru catalysts proceeds through several elementary steps. At first, methanol molecules are dehydrogenated, thereby producing organic fragments, mainly carbon monoxide ͑CO͒, that chemisorb and build up at the catalyst surface. CO fragments are subsequently oxidized to CO 2 by adjacent hydroxyl groups ͑-OH͒ that also form at the catalyst surface in the presence of water.1 Finally, CO 2 is liberated, thereby allowing turnover of the catalytic sites. To some extent, depending on the anodic potential, methanol may not be fully dehydrogenated to CO. In this case, further oxidation of the resulting dehydrogenation fragments generates formic acid or methylformate in place of CO 2 .2,3 Many investigators believe that methanol electro-oxidation occurs through a bi-functional mechanism: methanol molecules are adsorbed and dehydrogenated at Pt sites, whereas surface bonded-OH groups are preferentially formed at the Ru sites by water dissociation ͗PtCO ads + Ru − OH → Pt + Ru + CO 2 ↑ + H + + 1e − ͘ A good review on the bifunctional mechanism can be found in Ref. 1. Other investigations, however, suggest that the main role of ruthenium in the alloyed catalyst is a modification in the platinum electronic structure, which causes significant weakening of the CO chemisorption bond at Pt sites thereby enhancing the turnover rate. 4 Whether the promoting effect of Ru can be ascribable to a bifunctional mechanism or to weakening of the Pt-CO chemisorption bond, it is clear that the most effective catalysts for methanol electro-oxidation must be based on Pt-Ru combinations. Despite considerable advance in development of these ele...

Synthesis and characterization of quaternary PtRuIrSn/C electrocatalysts for direct ethanol fuel cells

“…It is known that along with Ru and Sn, Ir also activates and promotes the electro-oxidation of adsorbed CO-like species, as seen in DEFC [19] and DMFC [20,21]. de Tacconi et al [22] investigated ethanol oxidation on Ir and Rh electrodes by the FTIR method, and they found that electro-oxidation of ethanol on Ir is selective and produces mainly acetic acid, while on Rh it produces CO 2 .…”

Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

“…Subsequent cooling of the chamber results in deposition of the metal clusters onto the substrate surface. Then the precursor impregnated substrate is kept at high temperature (~300 °C) under nitrogen atmosphere to decompose and yield PtRu bimetallic nanoparticles [61]. In plasma sputtering method, Pt and Ru targets are faced to the substrate (carbon support) at a specific distance, in a vacuum chamber.…”

PtSnIr/C anode electrocatalysts: promoting effect in direct ethanol fuel cells

“…Moreover, these catalysts also exhibit excellent performance in the electrocatalysis of methanol in direct methanol fuel cells (DMFCs). 22, 23 Chen et al 24 showed that a thin layer of IrO 2 on Ti/IrO 2 /Pt improved the activity of these electrodes for methanol electrooxidation. They demonstrated that the current density increased and that the onset potential for methanol electrooxidation also shifted over 200 mV downward compared to the Ti/Pt nanoparticles.…”

“…Nevertheless, IrO 2 is extensively used in the preparation of mixed oxide electrodes, and numerous reports have suggested the application of Ir and its oxides in fuel cell systems. 22,[27][28][29] Indeed, results obtained through in situ Fourier transform infrared (FTIR) studies for ethanol electrooxidation on Ir electrodes 30 (Pt electrodes containing some Ir or its oxides and quaternary electrocatalysts) showed that these systems perform well for ethanol oxidation in a direct ethanol fuel cell.Considering these results, it is evident that the presence of Ir in the electrocatalyst has a synergetic effect (generally with Pt) for both ethanol oxidation and direct ethanol fuel cell performance. Therefore, the aim of this work is to produce an optimized PtSnIr/C electrocatalyst, prepared by polymeric precursor method, to be used for both ethanol oxidation and as anode in a direct ethanol fuel cell.…”

“…Nevertheless, IrO 2 is extensively used in the preparation of mixed oxide electrodes, and numerous reports have suggested the application of Ir and its oxides in fuel cell systems. 22,[27][28][29] Indeed, results obtained through in situ Fourier transform infrared (FTIR) studies for ethanol electrooxidation on Ir electrodes 30 (Pt electrodes containing some Ir or its oxides and quaternary electrocatalysts) showed that these systems perform well for ethanol oxidation in a direct ethanol fuel cell.…”