Four ternary catalysts, Pt-Ag-Ru, Pt-Au-Ru, Pt-Rh-Ru, and Pt-Ru-W 2 C, were investigated as anode electrocatalysts for oxidation of hydrogen-containing carbon monoxide. These catalysts were either alloys or intimate admixtures of the components. Membrane electrode assemblies were prepared for all the catalysts with anode Pt loading of 0.4 mg/cm 2 , and anode polarization was determined for oxidation of a H 2 stream containing 104 ppm CO. Potentials for CO oxidation were determined by stripping preadsorbed CO using cyclic voltammetry. The Pt-Ru-W 2 C ͑1:1:0.4 molar ratio͒ oxidizes CO at a lower potential, and the polarization for oxidation of hydrogen-containing CO was lower than the widely used Pt-Ru ͑1:1 molar ratio͒ catalyst. At low polarization, the Pt-Ru-W 2 C catalyst showed twice the activity of the Pt-Ru catalyst when the oxidation currents were normalized to the Pt area.

No abstract

In this study, transition metal complexes of amines and macrocycle ligands like cyclam, porphyrin, and phthalocyanine were studied as catalysts with Pt for electrochemical oxidation of hydrogen containing CO. These complexes are believed to act as redox mediators in generating species that oxidize CO. A systematic approach was used to improve CO tolerance of Pt electrocatalysts using the redox potential of the macrocycle complex as a guideline. Anode polarization for oxidation of H 2 containing 104 ppm CO was lowered when ruthenium tetramethylcyclam ͑RuTMC͒, molybdenum tetrakis͑methoxyphenyl͒porphyrin ͑MoT-MPP͒, and hexaammine ruthenium chloride were used as co-catalysts with Pt. The anode polarization is reduced by 40% when MoTMPP is used as co-catalyst with Pt. The anode polarization for these catalysts shows a direct correlation with the redox potential of the complexes and decreases linearly with a reduction in the redox potential of the complex. Further improvements in CO tolerance could be obtained by increasing the electroactive population of the complex and its proximity to Pt crystallites.Fuel cells show promise as energy conversion devices and are increasingly being considered for automotive and small-to-medium scale electrical power generation applications. 1 The proton exchange membrane fuel cell ͑PEMFC͒ is of interest for transportation applications primarily due to its low operation temperature ͑80°C͒, ease of fabrication, and its high energy density.One of the major challenges in using PEMFCs for transportation applications is the loss of power output due to CO poisoning of the Pt catalyst when running on hydrogen produced by reforming hydrocarbons. With 25 ppm CO, the maximum power density obtained in a PEMFC operating at 80°C and 0.24 MPa ͑3.4 psig͒ having an anode and cathode noble metal loading of 1 mg/cm 2 was observed by Oetjen et al. to drop to 0.3 W/cm 2 from a power density of 0.75 W/cm 2 for pure H 2 . 2 The anode polarization for oxidation of pure hydrogen on Pt in a PEMFC is small, about 0.1 V at a current density of 2 A/cm 2 at 85°C and a pressure of 16 psig. 3 However Pt is poisoned by chemisorbed CO when even a few parts per million CO is present in the fuel stream, 4 reducing the Pt area available for hydrogen oxidation. On-line CO removal from the hydrogen stream adds to the system complexity and cost.Pt-Ru ͑1:1 atomic ratio͒ is a widely used CO-tolerant binary alloy catalyst, where Ru is believed to assist in the oxidation of the CO through chemisorbed -OH at potentials as low as 0.25 V. 5 Even this catalyst suffers a loss in power density of 25 and 40% 2 when the anode feed contains 25 and 100 ppm CO, respectively, in a PEMFC at 80°C and a pressure of 1 atm. Injection of 4.5% O 2 in the fuel stream to selectively oxidize CO was found to restore the performance with 100 ppm CO. 6 This approach is not preferred due to the added complexity and safety issues with the O 2 injection.Here, an approach involving the use of organic metal macrocycle complexes with Pt is used to address thi...

Tolerance to small amounts of CO is important for proton exchange membrane fuel cells ͑PEMFCs͒ operating on hydrogen obtained by reforming carbon-based fuels. Platinum-based catalysts used today suffer high anode polarization losses, reducing performance and fuel efficiency. Here, findings in the search for CO-tolerant catalysts are reported. Novel platinum-based catalysts were discovered that show low polarization for oxidation of hydrogen containing 104 ppm CO, and little adsorbed CO was observed in CO stripping studies. Platinum in these catalysts is believed to have sulfur in its structure obtained from sodium thiosulfate used in the synthesis of the Pt catalysts. The activity of the catalyst varies with the amount of free platinum surface available, with one catalyst showing better activity than the Pt-Ru catalyst. Sulfur present in the catalysts resulted in redox activity at lower potentials than that shown by adsorbed sulfur on Pt and was stable during cyclic potential sweeps.

FuelCell Energy, Inc. (FCE) is a global leader in providing ultra-clean baseload distributed generation at more than 50 locations worldwide. These plants have generated more than one billion kilowatt hours of ultra-clean power using a variety of fuels including renewable biogas, coal-bed methane, propane, and natural gas. The generator design is based on the internal reforming direct carbonate fuel cell (DFC®) concept. The key to widespread fuel cell commercial acceptance is grid competitive cost of electricity (COE). The prime contributor to the fuel cell COE is first-time and most importantly, periodic replacement costs of the fuel cell stack. As such, the focus of technology development is on reducing fuel cell cost as well as extending service. This paper reports on the progress on understanding and extending the carbonate fuel cell durability.