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Two physical vapor deposition (PVD) processes, magnetron sputtering (MS) and arc plasma deposition (APD), were investigated to prepare oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs). The catalysts are composed of Pt or Pt alloy on a NbOx decorated carbon support (NbOx/C). The combination of these materials results in tunable structures and electronic properties and a commensurate increase in lifetime (>60% retention after 30,000 cycles) and initial MEA mass activities of over 300 AgPt−1. In situ x-ray absorption spectroscopy (XAS) shows that there exists direct interaction between Pt and the O in the non-stoichiometric NbOx in Pt on NbOx/C catalyst. The introduction of Co leads to shortened Pt–Pt bond distance as confirmed by XAS, and a beneficial Pt on NbOx strain effect. The relationship between Pt and NbOx loading is discussed based on rotating disk electrode (RDE) data.

Single-cell and half-cell degradation test procedures were evaluated for carbon-supported Pt/C, PtCo/C and PtNi/C catalysts. Half-cell analyses were employed to understand the effect of the number of cycles and of the scan rate over the cathode catalysts degradation under potential cycling from 0.6 to 1.2 V. The data suggested a time-dependent degradation for all three catalytic systems. Single-cell measurements were used to evaluate the impact of catalyst degradation on fuel cell performance. The measurements in both setups showed similar ECSA and ORR mass activity losses. Specific degradation mechanisms related to Pt dissolution, Pt agglomeration, and transitional metal leaching were quantified and correlated with performance losses.

This work uses a carbon-supported amorphous conductive metal oxide as Pt-based catalyst support for ORR in PEMFC. Amorphous conductive metal oxides have neither grain boundaries, nor the long-range atomic order to be easily transformed into insulating crystalline structure, i.e. amorphous niobium oxides are resistant to oxygen incorporation, thus preserving the structural stability and electric conductivity.

Single-cell and half-cell degradation test procedures are evaluated for carbon supported Pt catalysts. Half-cell analyses are employed in identification of specific test parameters for evaluation of cathode catalysts. Single-cell measurements run at 100 % relative humidity (RH) evaluate the impact of catalysts degradation on fuel cell performance. The measurements in both setups show a 20 % deviation of the electrochemical surface area loss (ECSA), while the oxygen reduction reaction (ORR) activity losses were comparable. The quantification of specific degradation mechanism as Pt dissolution and particle agglomeration and correlation with surface area and oxygen reduction activity is discussed.

Pulse voltammetry as a technique was used to explore the conditions under which platinum oxides form in an operating fuel cell. The technique is shown to have high sensitivity towards adsorbed surface species, and is useful for the realization of pulse type in situ fuel cell experiments.

The results of a successful U.S. Department of Energy (DoE) funded two-year $2.9 MM program lead by GrafTech International Inc. (GrafTech) are reported and summarized. The program goal was to develop the next generation of high temperature proton exchange membrane (PEM) fuel cell bipolar plates for use in transportation fuel cell applications operating at temperatures up to 120 °C. The bipolar plate composite developed during the program is based on GrafTech’s GRAFCELL resin impregnated flexible graphite technology and makes use of a high temperature Huntsman Advanced Materials resin system which extends the upper use temperature of the composite to the DoE target. High temperature performance of the new composite is achieved with the added benefit of improvements in strength, modulus, and dimensional stability over the incumbent resin systems. Other physical properties, including thermal and electrical conductivity of the new composite are identical to or not adversely affected by the new resin system. Using the new bipolar plate composite system, machined plates were fabricated and tested in high temperature single-cell fuel cells operating at 120 °C for over 1100 hours by Case Western Reserve University. Final verification of performance was done on embossed full-size plates which were fabricated and glued intomore » bipolar plates by GrafTech. Stack testing was done on a 10-cell full-sized stack under a simulated drive cycle protocol by Ballard Power Systems. Freeze-thaw performance was conducted by Ballard on a separate 5-cell stack and shown to be within specification. A third stack was assembled and shipped to Argonne National Laboratory for independent performance verification. Manufacturing cost estimate for the production of the new bipolar plate composite at current and high volume production scenarios was performed by Directed Technologies Inc. (DTI). The production cost estimates were consistent with previous DoE cost estimates performed by DTI for the DoE on metal plates. The final result of DTI’s analysis for the high volume manufacturing scenario ($6.85 /kW) came in slightly above the DoE target of $3 to $5/kW. This estimate was derived using a “Best Case Scenario” for many of the production process steps and raw material costs with projections to high volumes. Some of the process improvements assumed in this “Best Case Scenario” including high speed high impact forming and solvent-less resins, have not yet been implemented, but have a high probability of potential success.« less

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Normal pulse voltammetry (NPV) is applied to operating proton exchange membrane fuel cells (PEMFCs) using a high current potentiostat. Kinetic information including the Tafel slope and exchange current density for the oxygen reduction reaction (ORR) is directly extracted from the steady state voltammetric response obtained from the NPV experiment. Temperature, relative humidity, and conditioning potential are varied independently to observe their effect on the PEMFC through the Tafel slope calculation. This NPV technique provides kinetic information previously collected through ex situ techniques such as rotating disc electrodes. The ability to probe in situ the kinetic effects of catalysts within operational PEMFCs has never been proposed in this detail. NPV measurements take less than 30 seconds to conduct thus making the process simple and efficient. The observed Tafel slope is about 60mV/decade for oxide covered platinum and 120mV/decade for oxide free platinum.

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Pulse Voltammetry is a useful technique in dealing with electrode processes at solid electrodes. Due to fast pulse times, the sensitivity of reverse pulse voltammetry to reactive intermediates can approach that of a rotating ring disk electrode. In reverse pulse voltammetry, the electrode is held at a separate conditioning potential to grow or strip the platinum oxide before a pulse is applied. This conditioning potential controls the initial thickness of the oxide, and leads to a uniform oxide condition before each pulse experiment. In this paper, we explore the use of a pulse voltammetry technique to control over the growth conditions of the platinum oxide over an electrochemically clean surface.

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