Qinbai Fan

Catalyst Microstructure Examination of PEMFC Membrane Electrode Assemblies vs. Time

A series of single-cell, hydrogen-air proton exchange membrane fuel cells (PEMFCs) was operated for different lengths of time, namely, 200, 500, 700, and 1000 h. A group of reproducible and identical membrane electrode assemblies (MEAs) was used for those tests. Cell performance was studied by examining the cell polarization curves. After various lifetime tests, each MEA was cross-cut and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy, and Raman techniques to investigate any changes in catalyst structure and morphology, as well as particle size and chemical composition. The average particle size of the catalysts was calculated from XRD results and was found to increase with cell operating time. In addition, the agglomeration in nanometer-sized catalyst particles was observed from TEM analysis after prolonged cell operation. Ruthenium oxide was identified from Raman spectra of the anode catalyst from the tested MEAs, while no oxides were found on the cathode catalyst at the cell operating voltage. It is possible that the formation of metal oxides at the surface of the anode catalyst led to larger particles and ultimately resulted in the decrease of catalyst activity. This might be responsible for the slightly degraded cell performance following 700 h of operation.

Multilayer Nano Ti ∕ TiO2 – Pt Electrode for Coal-Hydrogen Production

Multilayer nanoporous Ti/TiO{sub 2} films were obtained by controlling electro-oxidation potentials in a sulfuric acid solution. After etching in a dilute hydrogen fluoride solution, the porous layers were deposited and intercalated with Pt and Pt-Ru to form Ti/TiO{sub 2}-Pt and Ti/TiO{sub 2}-PtRu electrodes by using the cyclic voltammetric method. An electron diffraction spectroscopy was used to examine the electrode surface structure. The catalytic activity of the electrodes for electro-oxidation of coal shows that the multilayer nanoporous Ti/TiO{sub 2}-Pt structure improves the electrode performance in comparison to a pure Pt electrode and a Pt coated Ti electrode. The Ti/TiO{sub 2}-Pt-Ru (1: 2) electrode shows even better catalytic activity than the Ti/TiO{sub 2}-Pt. Anode gas analysis shows that the coal electro-oxidation produces mainly CO{sub 2} with trace amount of CO and the cathode gas is pure hydrogen. We also observed some lower hydrocarbon by-products, such as methane. The amount of CO{sub 2} is only about 10% of the amount of H{sub 2} produced.

In-situ Raman Examination on PtRu/C in PEMFC

PtRu/C catalyst before and after a lifetime test in a proton exchange membrane fuel cell (PEMFC) has been characterized insitu using Raman spectroscopy. It was found that the formation and stability of ruthenium oxide were extremely sensitive to atmospheres and less dependent on temperatures in the range of 25 o C ∼ 100 o C. Amorphous ruthenium oxide was rapidly reduced by the presence of hydrogen and readily oxidized when air or water vapor was introduced. The formation and reduction of ruthenium oxide might change the PtRu binary structure and lead to catalyst degradation along with carbon corrosion, which could jeopardize the fuel cell performance and stability.

Correlations between Microstructures and Properties of Pd-modified Nafion® Membranes

Conference Name:8th Symposium on Proton Exchange Membrane Fuel Cells. Conference Address: Honolulu, HI. Time:OCT, 2008.

In Situ AC Impedance Diagnosis of Hydrogen Oxidation in a PEMFC

The effects of gas flow rate, temperature and applied voltage on hydrogen oxidation at Pt-Ru/C electrodes were systematically investigated by electrochemical impedance spectroscopy (EIS) and liner sweep voltammetry (LSV). The kinetic parameters of polarization resistance (Rp/R2) and double layer capacitance (C2) were obtained by fitting the impedance data with the equivalent circuit. The charge transfer resistance (Rct) which is identical to Rp in this study was also determined by analyzing the LSV data. The contribution of hydrogen oxidation to the cell lifetime was studied by in situ impedance measurement at different periods of time during durability test using a simulated PEMFC. It was found that the R2 or Rct values increased with decreases in gas flow rate and temperature and increase of applied voltage. Anode impedance increased rapidly after 100h of continuous test, and was nearly 1/3 to the cell impedance at 25 o C. The changes in high-frequency parameters were related to the microstructure of the catalyst layer.