Dissolution of Transition Metals in Combinatorially Sputtered Pt[sub 1−x−y]M[sub x]M[sub y][sup ʹ] (M, M[sup ʹ]=Co, Ni, Mn, Fe) PEMFC Electrocatalysts

Abstract

The stability of Pt-based or other metallic alloys under the corrosive working conditions of proton exchange membrane fuel cells ͑PEMFCs͒ is an important factor to consider in the search for improved PEM electrocatalysts. The dissolution of transition metals ͑Co, Ni, Mn, Fe͒ from Pt 1−x−y M x M y Ј electrocatalysts after operation in PEM hydrogen fuel cells or after treatment in 1 M H 2 SO 4 at 80°C is reported. Catalyst libraries were prepared by combinational sputtering on nanostructured thin-film supports that were used directly in fuel cells and for acid testing. In each library the Pt mass loading was kept fixed at 0.1 mg cm −2 while the amounts of M and MЈ varied with position. The transition metal content of all compositions of all libraries, determined by electron microprobe, was significantly reduced in the same way after fuel cell or acid testing. Samples with x + y ജ 0.25 before fuel cell or acid testing were found with x + y Ϸ 0.25 after exposure due to the dissolution of transition metals, independent of the choice of M and MЈ for the elements studied here. We suggest that the composition Pt 1−x−y M x M y Ј with x + y Ϸ 0.25 is near the percolation limit for diffusion of transition metals from the interior of the alloy. The acid treatment described here mimics fuel cell testing from a corrosion standpoint and hence can be used as a simpler, ex situ test for PEM electrocatalysts.At present, polymer electrolyte membrane fuel cells ͑PEMFCs͒ are under intense research because they provide one avenue for "green" electricity production. However, prior to the successful commercialization of hydrogen fuel cells, besides fuel-related issues, numerous other shortcomings need to be addressed. 1-3 Materials challenges for the fuel cell include low-cost proton conducting membranes, as well as economical high-performance catalysts for both fuel and oxidant electrodes. For the cathode catalyst, where the oxygen reduction reaction ͑ORR͒ takes place, improvement of the kinetic activity is highly desired because an overvoltage of about 400 mV, or about 70% of the total losses in a typical PEMFC, occurs at this electrode. Although the effects of numerous factors like catalyst composition, catalyst grain size, crystalline facets, support structures, etc., on the ORR have been studied, details of the ORR mechanism still remain elusive. [4][5][6][7][8] Current ORR catalysts consist of nanometer-size Pt particles supported on carbon black. When the dispersion of Pt particles on highsurface-area carbon supports reaches its limits, further improvements in activity, durability, and cost reduction can be achieved by new catalyst formulations such as Pt alloys, non-Pt-based catalysts, and/or the development of new support structures. 9-12 Other current ideas that are actively explored in improving the catalytic activity and lowering the Pt content involve Pt monolayers on active alloy cores, metal oxides and strong metal-support interactions, and additives such as heteropolyacids. [13][14][15][16][17] Binary and ternary Pt tran...

Electrochemical and Microstructural Evaluation of Aged Nanostructured Thin Film Fuel Cell Electrocatalyst

“…The fcc lattice constants for pure Pt NSTF was in good agreement with literature values [32][33][34] . The lattice constants and grain sizes were calculated using the Bragg and Scherrer equations, respectively, by fitting Gaussian profiles to the measured data.…”

Dynamic Behavior of a PEM Fuel Cell During Electrochemical CO Oxidation on a PtRu Anode

“…However, even traces (ppm) of carbon monoxide (CO) in the hydrogen feed gas can cause serious performance degradation of PEMFCs [1][2][3][4][5][6]. In order to achieve higher power output with CO containing feed in fuel cells, the utilisation of bimetallic anode catalysts, PtM/C, have been largely investigated [1][2][3][6][7][8][9][10][11][12]. The influence of Ru, Mo, Sn with Pt as anode catalyst is intensively studied.…”

High Throughput Thin Film Pt-M Alloys for Fuel Electrooxidation: Low Concentrations of M (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh)

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