Enhanced CO Tolerance Research Articles

UHV, Electrochemical NMR, and Electrochemical Studies of Platinum/Ruthenium Fuel Cell Catalysts

It is well-known that platinum/ruthenium fuel cell catalysts show enhanced CO tolerance compared to pure platinum electrodes, but the reasons are still being debated. We have combined cyclic voltammetry (CV), temperature programmed desorption (TPD), electrochemical nuclear magnetic resonance, and radio active labeling to probe the origin of the ruthenium enhancement in Pt electrodes modified through Ru deposition. The results prove that the addition of ruthenium not only modifies the electronic structure of all the platinum atoms but also leads to the creation of a new form of adsorbed CO. This new form of CO may be ascribed to CO chemisorbed onto the “Ru” region of the electrode surface. TPD and CV results show that the binding of hydrogen is substantially modified due to the presence of Ru. Surprisingly though, TPD indicates that the binding energy of CO on platinum is only weakly affected. Therefore, the changes in the bond energy of CO due to the ligand effect only play a small role in enhancing CO to...

Electrosorption and catalytic properties of bare and Pt modified single crystal and nanostructured Ru surfaces

The electrosorption and catalytic properties of bare and Pt modified Ru(0001) and Ru(10−10) single crystal surfaces and carbon supported Ru nanoparticles have been studied by electrochemical, surface X-ray scattering, scanning tunneling microscopy, Fourier transform infrared spectroscopy and high resolution transmission electron microscopy techniques. The electrochemical surface oxidation of Ru(0001) in H 2SO 4 is an one-electron process resulting in 1 monolayer oxygen uptake and the increased spacing between the top two Ru layers from 2.13 Å at 0.1 V to 2.20 Å at 1.0 V. About 1/3 monolayer of bisulfate anions are coadsorbed with hydronium cations at low potentials. In HClO 4 solution, the adsorption process at ∼0.1 V is due to the surface oxidation apparently to RuOH rather than to hydrogen adsorption. The oxidation of Ru(10−10) is quite facile and a progressive growth of the oxide layer is observed in repeated potential cycles. Spontaneous deposition of a submonolayer-to-multilayer of Pt on metallic Ru surfaces is a new phenomenon involving a noble metal deposition on a noble metal substrate through a local cell mechanism. The electrocatalysts prepared by spontaneous deposition of Pt on Ru nanoparticles have high activity and high CO tolerance exceeding those of the state-of-the-art commercial catalysts containing several times higher Pt loadings. Electronic effects appear to play a role in providing enhanced CO tolerance of Pt submonolayers on Ru nanoparticles.

Performance of a Polymer Electrolyte Membrane Fuel Cell Exposed to Transient CO Concentrations

The response of Gore’s advanced PRIMEA® Series 5561 membrane electrode assembly (MEA) exposed to transient concentrations of CO in the anode feed was studied for a 25 laboratory-scale polymer electrolyte membrane fuel cell (PEMFC). The data include relatively high (500 and 3000 ppm) CO levels at 70°C cell temperature, low reactant stoichiometry, and atmospheric pressure, conditions that may be typical for stationary PEMFC applications. Poisoning and recovery rates are reported for saturated conditions and these rates are compared for two types of gas diffusion media [single-sided ELAT® and CARBEL™ CL gas diffusion media (GDM)] and for conditions with and without air-bleed treatments. It is shown that a 5% air bleed provides a current density of 1.0 A/ at 0.6 V for CARBEL CL GDM exposed to 500 ppm CO/ mixtures. The data show that the transient performance at 0.6 A/ with this MEA and relatively high concentrations of CO is a result of an interaction of CO kinetics and mass transfer through the GDM. Indirect evidence of electrochemical oxidation of CO during the transient pulses with 3000 ppm CO is presented. The data discussed in this paper are suitable for verifying numerical models of a PEMFC and establishing a baseline for new recovery schemes using new MEAs with enhanced CO tolerance. In addition, the results have implications for the design of reformate fuel processing systems and the use of effective control schemes to prevent CO transients. © 2001 The Electrochemical Society. All rights reserved.

Investigation of Enhanced CO Tolerance in Proton Exchange Membrane Fuel Cells by Carbon Supported PtMo Alloy Catalyst

E-TEK, Incorporated, Natick, Massachusetts 01760, USAWe report a two- to threefold enhancement of CO tolerance in a proton exchange membrane (PEM) fuel cell, exhibited by carbonsupported nanocrystalline PtMo/C as compared to the current state of the art PtRu/C electrocatalysts. The bulk of these nanocrys-tals were comprised of Pt alloyed with Mo in the ratio 8.7:1.3 as shown by both X-ray diffraction and in situ extended X-ray ab sorp-tion fine structure measurements. Rotating disk electrode measurements and cyclic voltammetry in a PEM fuel cell indicate theonset of CO oxidation at potentials as low as 0.1 V. Further, the oxidation of CO exhibits two distinct peaks, indicating redox b ehav-ior involving oxyhydroxides of Mo. This is supported by in situ X-ray absorption near edge structure measurements at the Mo Kedge.© 1999 The Electrochemical Society. S1099-0062(98)08-029-8. All rights reserved.Manuscript submitted August 10, 1998; revised manuscript received September 28, 1998. Available electronically October 30, 1998.

Enhanced CO Tolerance in Polymer Electrolyte Fuel Cells with PtMo Anodes

We demonstrate that fuel cells using supported PtMo anode electrocatalysts can exhibit excellent tolerance to 20 ppm CO in H 2 . Only some of the supported PtMo samples tested appeared highly tolerant to CO. A key factor correlating with good anode performance in the presence of CO is the particle size of the supported PtMo catalyst.