Investigation of Direct Methanol Fuel Cell Electrocatalysts Using a Robust Combinatorial Technique

Abstract

A combinatorial approach to batch fabricating and evaluating fuel cell catalyst surfaces is described. The well-known binary Pt/Ru alloy and two compositional regimes of a novel quaternary Ni/Zr/Pt/Ru system were examined in detail. Catalyst films no thicker than 10 nm were deposited onto an array of 36 gold electrodes 0.5 cm 2 in area that were microfabricated on a 12.5 ϫ 12.5 cm glass substrate. The catalyst films had identical bulk and surface compositions, a result of the atom-level mixing that occurred during the room-temperature cosputtering method used. A multichannel pseudopotentiostat was implemented for electrochemical screening. Compositions with promising and/or contrasting catalytic activities were also studied using X-ray diffraction, X-ray energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. A low-Pt-content Ni 31 Zr 13 Pt 33 Ru 23 film was found to exhibit nominally the same activity ͑at 0.45 V vs a normal hydrogen electrode in 1 M H 2 SO 4 , 1 M CH 3 OH͒ as the best PtRu alloys studied. This material had a fundamentally different crystal and electronic structure than that observed in the Pt/Ru films and exhibited a significantly higher degree of Pt site utilization. These results were consistent with the existence of a catalytic reaction pathway different than that reported for Pt/Ru. Methodologies for optimizing anode catalysts for direct methanol fuel cells ͑DMFCs͒ have been under development since the 1980s. 1 A primary goal has been to minimize the cost associated with mass-producing fuel cells by limiting or even eliminating the amount of precious metal necessary for achieving good electrical performance. Typically, DMFC anode assemblies consist of a fibrous carbon paper loaded with 2-8 mg/cm 2 of Pt/Ru black. Efforts to improve the electrocatalytic activity have focused on maximizing the surface-area-to-volume ratio of the catalyst materials, either by creating nanostructured powder materials or by dispersing small catalyst grains on larger carbon particles. [2][3][4] Other results have shown that alternate chemistries may be appealing, and several research groups have reported catalyst alloy materials that contain little or no Pt yet retain some catalytic functionality. In particular, it has been demonstrated that the addition of Ni, Co, V, Fe, Cu, and Mo to Pt/Ru may enhance catalyst performance. 5-7 Others have found that some binary alloys containing Ni and Ti, Nb, Ta, or Zr can function as Pt-free methanol catalysts, though the reported current densities are substantially lower than those typically reported for commercial Pt/Ru powders. 8,9 In many of the studies on novel catalysts, the actual mechanisms driving the reactions of interest are not well described. There are multiple, sometimes contradictory theories used to explain the observed effects. [10][11][12][13] Confounding this issue is the fact that contrasting ͑often unpublished and proprietary͒ synthesis routes are used to create catalyst materials ͑typically in powder form͒, each resulting in significantly di...

Applications of high throughput (combinatorial) methodologies to electronic, magnetic, optical, and energy-related materials

“…The Pt-Ru-Ni-Ti quaternary system was also investigated, with particular attention to mitigating the effects of surface morphology and segregation effects. 378 A low Pt content catalyst (Ni 31 Zr 13 Pt 33 Ru 23 ) was discovered 378 which exhibited similar current densities to Pt 84 Ru 16 catalysts, with an onset voltage that was 150 mV lower, Fig. 78.…”

Durable Transition‐Metal‐Carbide‐Supported Pt–Ru Anodes for Direct Methanol Fuel Cells

“…Ru (3p 3/2 ) spectrum for Pt-Ru/C can be deconvoluted into two distinct peaks at 461. 4 [20]. Figure 3(a) shows electro-catalytic activities for Pt-Ru/C, Pt-Ru/MoC, and Pt-Ru/WC towards methanol oxidation reaction (MOR).…”

“…Carbon-supported Pt-Ru (Pt-Ru/C) is the most effective catalyst for methanol electro-oxidation in direct methanol fuel cells (DMFCs) [1][2][3][4]. But the long-term stability of Pt-Ru electro-catalyst is a serious problem as Ru from the Pt-Ru anode tends to cross through the proton exchange membrane and deposit on to the Pt cathode affecting its performance [5].…”

Catalysts for the electro‐oxidation of small molecules

“…However, there have been a few systematic researches on the temperature dependencies of the electrocatalytic activities for the MOR, [9,[45][46][47][48] and their methods are not always adopted easily.…”

“…• C. For the use of Pt-skin-type alloys in the MOR at higher temperature, the addition of a corrosion-resistant metal component [48] as well as stable oxides [6] may be effective to modify the electronic structure and to supply the OH species.…”