Donald Tryk

Heat-treated polyacrylonitrile-based catalysts for oxygen electroreduction

Polyacrylonitrile (PAN), mixed with Co(II) or Fe(II) salts and high-area carbon and then heat treated, has been found to yield very promising catalysts for O2 reduction in concentrated alkaline and acid solutions. The catalytic activities are comparable to those for the heat-treated corresponding transition metal macrocycles and polypyrrole black-based catalysts. The addition of the transition metal to the nitrogen-containing polymer, either before or after the heat treatment with carbon, is an important factor for good activity. The nitrile nitrogen of the PAN is probably retained and converted to pyridyl nitrogen during the heat treatment, and this nitrogen is believed to provide binding sites for the transition metal ions, which then act as catalytic sites for oxygen reduction to peroxide and its decomposition.

Methanol-tolerant electrocatalysts for oxygen reduction in a polymer electrolyte membrane fuel cell

Heat-treated μ-oxo-iron(iii) tetramethoxy phenyl porphyrin (Fe-TMPP)2O and iron(iii) tetramethoxy phenyl porphyrin (FeTMPP-Cl) as well as iron(iii) octaethyl porphyrin (FeOEP-Cl) adsorbed on high-area carbons such as deashed and un-deashed RB carbon (Calgon) and Black Pearls-2000 (Cabot) have been found to exhibit stable and very high oxygen reduction rates. Experiments done over a period of 24h showed no performance degradation. Measured performances were very similar to supported platinum (E-Tek), when tested in 85% H3PO4-equilibrated Nafion 117 membrane at 125°C and hydrated-Nafion membrane at 60°C in a minifuel cell. The macrocycle cathodes are insensitive to the presence of methanol whereas the platinum cathodes are very sensitive and show degradation in the oxygen reduction performance.

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Electrocatalysis for oxygen electrodes in fuel cells and water electrolyzers for space applications

Abstract The lead ruthenate pyrochlore Pb 2 Ru 2 O 6,5 , in both high- and low-area forms, has been characterized using thermogravimetric analysis, X-ray photo-electron spectroscopy, X-ray diffraction, cyclic voltammetry, and O 2 reduction and generation kinetic—mechanistic studies. Mechanisms are proposed. Compounds in which part of the Ru is substituted with Ir have also been prepared. They exhibit somewhat better performance for O 2 reduction in porous, gas-fed electrodes than the unsubstituted compound. The anodic corrosion resistance of pyrochlore-based porous electrodes was improved by using two different anionically conducting polymer overlayers, which slow down the diffusion of ruthenate and plumbate out of the electrode The O 2 generation performance was improved with both types of electrodes. With a hydrogel overlayer, the O 2 reduction performance was also improved.

Novel in situ and ex situ techniques for the study of lithium/electrolyte interfaces

Various aspects of the reactivity of lithium toward propylene carbonate (PC) and poly(ethylene oxide) (PEO) have been examined using ex situ and in situ spectroscopic techniques, respectively. Temperature programmed desorption of perdeuterated PC (d6-PC) layers condensed at about 150 K on a clean Li film supported on an Au foil yielded a broad m/e peak, at temperatures in the range from 220 to 520 K (and thus much lower than that found for Li2CO3), which was tentatively ascribed to the thermal decomposition of a lithium alkyl carbonate. A spectroelectrochemical cell/environment controlled chamber has been designed and constructed to examine Li/PEO(LiClO4) electrolyte interfaces formed by Li electrodeposition on to a thin Au layer sputtered on the surface of a Ge internal reflection element in situ using attenuated total reflection Fourier-transform infrared (ATR/FT-IR) spectroscopy. This assembly enables variable temperature measurements to be performed under conditions of utmost cleanliness. Preliminary results have indicated that in the case of PEO/LiClO4 this ATR/FT-IR technique has sufficient sensitivity to observe changes in the composition of the surface and near surface region, including reaction products and perchlorate anions, which contribute to the transport of charge in the electrolyte phase.

Transition-Metal Oxide Electrocatalysts for O2 Electrodes: The Pyrochlores

There has been wide interest in the search for bifunctional oxygen electrocatalysts which can reversibly or nearly reversibly catalyze both the reduction and the generation of O2. There are two possible approaches: (1) use of a single bifunctional electrocatalyst which promotes both reactions; and (2) use of separate electrocatalysts for the two reactions within one electrode. Both approaches have been tried by various groups. The use of separate catalysts for these two functions provides a much wider range of materials for consideration. In this chapter, however, the first approach will be emphasized, with the focus on the transition-metal pyrochlore oxides, particularly the lead ruthenate pyrochlore and related materials. These pyrochlores have metallic conductivity, can be prepared in very high area forms, and also show high electrocatalytic activity for both O2 reduction and generation.(1–4) The nature of the electrocatalysis is also very much dependent on the surface electronic properties of the catalyst, which in turn are dependent to some extent on the bulk properties.