High Energy Ballmilled Pt-Mo Catalysts for Polymer Electrolyte Fuel Cells and Their Tolerance to CO

Abstract

Polymer electrolyte fuel cells are clean, efficient electrical generators based on the electrochemical oxidation of hydrogen by oxygen. Both electrochemical reactions require catalysts such as Pt to operate at a useful rate. However, Pt is easily poisoned by CO, and significant power losses may arise when H 2 is obtained from the reforming of alcohols or hydrocarbons. Even 10 ppm CO in the H 2 feedstream has a detrimental effect on the fuel cell performance. 1 Binary electrocatalysts have been used with success to alleviate CO poisoning problems at the anode of polymer electrolyte fuel cells. They contain a more oxidizable element with the ability to activate oxygenated species at lower potentials in order to initiate CO oxidation. The most studied CO-tolerant anode catalysts are certainly Pt-Ru and Pt-Sn alloys (see Ref. 2 and references cited therein). Recently, several authors reported CO tolerance for new anode catalysts containing Mo which are of technical interest for low-temperature fuel cells fed with a reformed fuel and for direct methanol fuel cells (DMFCs). These catalysts are either binary Pt-Mo alloys [3][4][5][6][7][8] or ternary alloys such as Pt-Ru-Mo or Pt-Co-Mo, 7,9,10 or even composite Pt-based catalysts containing Mo oxides. 10-12 The best-performing CO-tolerant catalyst based on a Pt-Mo binary alloy has a Pt/Mo ϭ 4 surface atomic ratio. 3-6 It is of interest to develop Pt-Mo catalysts because Mo is a transition metal which is not expensive and is readily available. Furthermore, Mo is soluble in Pt, at least up to 28 wt %. 13 Pt-Mo alloys are also known in chemical catalysis, for instance to promote reactions of hydrocarbons with hydrogen. 14 High-energy ballmilling or mechanical alloying is an interesting low-temperature alloying technique. 15 The principle of mechanical alloying is simple. A vial containing the powder to be milled and the grinding balls is swung energetically several thousand times a minute. The balls impact at high velocity against the sample and the walls of the vial, thereby both milling and mixing the sample. Crystallites of nanometric dimensions are obtained during mechanical alloying. This paper is part of a series of articles intending to demonstrate that it is possible to adapt the technique of high-energy ballmilling to the preparation of interesting catalysts for fuel cells using a protonic membrane, e.g., polymer electrolyte membrane (PEM) fuel cells and direct methanol fuel cell (DMFCs). As it is easy to prepare unsupported catalysts by high-energy ballmilling, this technique is particularly well-adapted for the production of catalysts for DMFCs, for which large amounts (from 1 to 5 mg of metal/cm 2 ) of Pt and CO-tolerant Pt alloys (usually Pt-Ru alloys) are used at the cathode and the anode, respectively. [16][17][18][19][20][21][22] However, before using mechanical alloying to prepare novel catalysts for the anode of DMFCs, it is necessary to demonstrate that this technique is able to produce well-known CO tolerant catalysts based on Pt and Ru or Pt and Mo. Pr...

X-ray Photoelectron Spectroscopic Analysis of Pt Nanoparticles on Highly Oriented Pyrolytic Graphite, Using Symmetric Component Line Shapes

“…The existence of surface PtO x has already been demonstrated in numerous studies ,− that showed that, in ultrahigh vacuum, molecular oxygen dissociates and chemisorbs onto Pt, even at cryogenic temperatures. In particular, Gouérec et al have shown, by in situ reduction in fuel cells, that oxidized Pt occurs exclusively at the nanoparticle surface. There are no reports of the true O:Pt atomic ratios.…”

CO adsorption in PdxCoyXz (X = Au, Mo, Ni) tertiary alloy nanocatalysts for PEM fuel cells-a theoretical analysis

“…Probable solution to overcome the poisoning effects in fuel cell is to use alloyed catalysts, such as Pt/Ru, Pt/Mo, Pt/Ru/Mo, Pt/Sn, Pt/Ru/WO 3 , etc. 22–25. A carbon‐supported Pd‐based PdPt catalyst with a Pd:Pt atomic ratio of 19:1 was synthesized and applied to a polymer electrolyte membrane fuel cell.…”

Pt-Ru catalysts prepared by high energy ball-milling for PEMFC and DMFC: Influence of the synthesis conditions

“…Since the mid-1990s, we have been developing the high energy ball-milling technique combined with a leaching procedure to produce unsupported Pt-based catalysts [28][29][30]. The high energy ball-milling technique, also called mechanical alloying, is a solid-state method for the synthesis of metallic powders or ceramics.…”