Hugh Middleton

Ammonia as a fuel in solid oxide fuel cells

The use of ammonia as a source of hydrogen for fuel cells has received little attention until now. Ammonia offers several advantages over hydrogen as a fuel and is produced commercially in massive quantities and as a biogas. This paper describes the results of a solid oxide fuel cell-based system running on ammonia and compares the performance with respect to hydrogen. A novel catalyst concept has been devised and employed with success. Results indicate that the ammonia performance, using the catalyst is comparable to hydrogen suggesting ammonia can be treated as an attractive alternative fuel.

Co-casting and co-sintering of porous MgO support plates with thin dense perovskite layers of LaSrFeCoO3

A tape casting co-sintering route is described in which thin dense layers of LaSrFeCoO3 (LSFC) have been formed on planar, porous MgO substrates 100- 200 micron thick. SEM analysis of the sintered structure showed that it was possible to eliminate most of the residual porosity in the LSFC layer, but maintain a porosity between 25 and 45% in the MgO support layer. The LSFC layer dit not reveal many cracks. The overall shrinkage of the co-sintered structure was about 25%. The LSFC layer topography was smooth and uniform with a metallic-like lustre. A good correlation was obtained between the observed microstructure and the gas permeability measurements made at room temperature.

A comparative evaluation of palladium and platinum nanoparticles as catalysts in proton exchange membrane electrochemical cells

The goal of the present study is the development and comparative characterisation of carbon-supported and nanostructured Pd- and Pt-based electrocatalysts for hydrogen oxidation in Proton Exchange Membrane (PEM) H2/O2(air) fuel cells and proton reduction in PEM water electrolysers. Catalysts have been synthesised in a solution using a combined impregnation/reduction polyol method. They have been characterised using X-ray Diffraction (XRD) analysis, Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and cyclic voltammetry. NanoPt, nanoPd and nanoPt-Pd catalysts deposited onto a carbon carrier have been used to prepare Membrane-Electrode Assemblies (MEAs) which, in turn, have been tested in PEM fuel cell and water electrolysis configuration. Using Pt0.5Pd0.5 (40 wt% on Vulcan XC-72) as a catalyst at the anodic side of a fuel cell, a typical cell voltage of 0.7 V was obtained at a current density of ca. 1.1 A cm −2 . Using Pd (40 wt% on Vulcan XC-72) as a catalyst at the cathodic side of an electrolysis cell, a typical voltage of 1.70 V was obtained at a current density of 1 A cm −2 . The electrochemical performances of the MEAs containing nanoPd-Vulcan were found similar to those obtained with nanoPt-Vulcan, either in fuel cell mode or electrolysis mode of operation. Palladium can, therefore, be used as an alternative catalyst for the hydrogen electrode in PEM electrochemical cells.

Evaluation of Thermoelectric Performance and Durability of Functionalized Skutterudite Legs

Thermoelectric generators are a promising technology for waste heat recovery. As new materials and devices enter a market penetration stage, it is of interest to employ fast and efficient measurement methods to evaluate the long-term stability of thermoelectric materials in combination with metallization and coating (functionalized thermoelectric legs). We have investigated a method for measuring several thermoelectric legs simultaneously. The legs are put under a common temperature gradient, and the electrical characteristics of each leg are measured individually during thermal cycling. Using this method, one can test different types of metallization and coating applied to skutterudite thermoelectric legs and look at the relative changes over time. Postcharacterization of these initial tests with skutterudite legs using a potential Seebeck microprobe and an electron microscope showed that oxidation and interlayer diffusion are the main reasons for the gradual increase in internal resistance and the decrease in open-circuit voltage. Although we only tested skutterudite material in this work, the method is fully capable of testing all kinds of material, metallization, and coating. It is thus a promising method for studying the relationship between failure modes and mechanisms of functionalized thermoelectric legs.

The Influence of Synthesis Procedure on the Microstructure and Thermoelectric Properties of p-Type Skutterudite Ce0.6Fe2Co2Sb12

We have investigated p-type skutterudite samples with the nominal composition Ce0.6Co2Fe2Sb12 synthesized from elementary constituents by gas atomization and conventional melting, and also those synthesized from ternary and binary phases such as FexCo1−xSb2 and CeSb2, respectively, which were mixed and subsequently ball-milled. We conducted measurements of the temperature-dependent transport properties (Seebeck coefficient, thermal/electrical conductivity) and carried out scanning electron microscope analysis, electron probe micro-analysis and powder x-ray diffraction to obtain information about microstructure and elementary distribution of the phases. We show that the presented synthesis methods each possess particular strengths but ultimately, however, lead to different final compositions of the skutterudite phase and secondary phases, which significantly influence the thermoelectric properties of the material. Material prepared using an educt method gave the best thermoelectric properties with a peak ZT of 0.7. Furthermore, we show that even an apparent homogeneous skutterudite area within the material exhibits varying stoichiometry in each grain even though they conform to the solubility range of cerium in this p-type skutterudite. Moreover, we show that marcasite is preferred as an educt over the arsenopyrite phase and discuss the formation of the p-type skutterudite phase with these synthesis techniques.