Stephen A. Campbell

In-situ methods for the determination of current distributions in PEM fuel cells

This article describes three different techniques for the determination of the current density distribution in operating fuel cells and compares their relative benefits with respect to ease of implementation and information gain. Real-time current density distribution data under steady state as well as transient conditions are presented and it is shown that they can contribute to an improved understanding of water management and reactant distribution over the active fuel cell area. The importance of these factors for the optimisation of fuel cell performance is discussed.

Ex situ Evaluation of Tungsten Oxide as a Catalyst Support for PEMFCs

The oxidation of carbon catalyst supports causes acute degradation in catalyst performance in proton exchange membrane fuel cells (PEMFCs). Tungsten oxide is considered here as a candidate material as an alternative catalyst support. A new method has been developed that allows Pt deposition on tungsten oxide catalyst supports. The electrochemical stability of tungsten oxide was studied by applying a coating of a tungsten-oxide-supported Pt catalyst to a rotating disk electrode and to a gold mesh. Accelerated oxidation tests were performed in deoxygenated 0.5 M H 2 SO 4 at 30 and 80°C. The oxidation stability of Pt/tungsten oxide and of Hispec 4000, a commercial catalyst, each coated on a gold mesh, was measured at 80°C. The oxygen reduction reaction (ORR) activity of Pt/tungsten oxide remained high, even after accelerated oxidation tests, while the ORR activity was extremely poor after accelerated oxidation tests of Hispec 4000.

Ex Situ and In Situ Stability of Platinum Supported on Niobium-Doped Titania for PEMFCs

The stability and activity of 10 mol % niobium-doped titania (10Nb-TiO 2 ) were compared to those of commercial Pt/C catalyst (HiSpec 4000), both ex situ and in a proton exchange membrane fuel cell. The stability test involved holding the cell at 1.4 V for 20 h. Fuel cell polarization curves were obtained both before and after the potential holds. Cyclic voltammogram data showed that the Pt surface area was stable for Pt/10Nb-TiO 2 even after holding for 60 h at 1.4 V. A significant drop in the Pt surface area was observed, however, for Pt/C after 20 h at 1.4 V. The high potential hold test showed significantly higher stability of the membrane electrode assembly with Pt/10Nb-TiO 2 compared to that with Pt/C.

Oxygen Reduction by Sol Derived [Co, N, C, O]-Based Catalysts for Use in Proton Exchange Membrane Fuel Cells

Two Co oxide sol-derived catalysts, one based on ethylenediamine and one on 1,2-phenylenediamine, were synthesized and examined for their oxygen reduction reaction (ORR) behavior in 0.5 M H 2 SO 4 . Supporting the catalyst on carbon powder significantly improved the catalyst performance, while heat-treatment of the carbon-supported catalysts at 650-900°C for 2 h under nitrogen dramatically improved its activity and selectivity. The ORR activity was further improved by increasing the concentration of the [Co, N, C, O]-based catalyst on carbon powder to 4% (wt % Co/C), employing the more aromatic 1,2-phenylenediamine ligand, and by using a ligand to Co ratio of 2:1.

Transmission Electron Microscope Observation of Pt Deposited on Nb-Doped Titania

Pt nanoparticles supported on niobium (Nb)-doped titania (TiO 2 ) were prepared using the alcohol reduction method. The 10 mol % Nb-doped TiO 2 (10Nb-TiO 2 ) was subjected to various heat-treatments. Depending on the heat-treatment either anatase or rutile 10Nb-TiO 2 was produced. The change in Pt morphology when deposited on 10Nb-TiO 2 supports that were treated under hydrogen at different temperatures was investigated by high-resolution transmission electron microscopy. Platinum particles deposited on rutile 10NbTiO 2 and anatase 10NbTiO 2 have distinctly different morphologies. Those deposited on anatase 10Nb-TiO 2 are similar to Pt/C and are essentially spherical. Platinum particles on rutile 10Nb-TiO 2 , however, appear flattened, indicating a strong metal-support interaction.