Ingeborg-Helene Svenum

Effect of Sb Segregation on Conductance and Catalytic Activity at Pt/Sb-Doped SnO2 Interface: A Synergetic Computational and Experimental Study

Antimony-doped tin dioxide (ATO) is considered a promising support material for Pt-based fuel cell cathodes, displaying enhanced stability over carbon-based supports. In this work, the effect of Sb segregation on the conductance and catalytic activity at Pt/ATO interface was investigated through a combined computational and experimental study. It was found that Sb-dopant atoms prefer to segregate toward the ATO/Pt interface. The deposited Pt catalysts, interestingly, not only promote Sb segregation, but also suppress the occurrence of Sb(3+) species, a charge carrier neutralizer at the interface. The conductivity of ATO was found to increase, to a magnitude close to that of activated carbon, with an increment of Sb concentration before reaching a saturation point around 10%, and then decrease, indicating that Sb enrichment at the ATO surface may not always favor an increment of the electric current. In addition, the calculation results show that the presence of Sb dopants in ATO has little effect on the catalytic activity of deposited three-layer Pt toward the oxygen reduction reaction, although subsequent alloying of Pt and Sb could lower the corresponding catalytic activity. These findings help to support future applications of ATO/Pt-based materials as possible cathodes for proton exchange membrane fuel cell applications with enhanced durability under practical applications.

Synthesis of Chromite for Subsequent Carburization by Methane-Hydrogen Gas Mixture

The syntheses of stoichiometric iron chromite and chromites with chosen impurity content have been developed using the induction skull melting technique. The aim for this synthetic material is to obtain pure samples to study the carburization by methane-hydrogen gas mixtures. For each synthesis, the parameters influencing the skull melting experiment have been considered. The product phases have been analyzed using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). The synthetic material was subsequently pelletized and sintered in argon. The use of excess iron was found to improve the quality of the final product as well as to help the melting. The difference in magnesium content between first and last solids formed seem to indicate a segregation phenomenon, while no evidence could support a similar trend for aluminum substitution in chromite.

New Insight to the Effects of Heat Treatment in Air on the Permeation Properties of Thin Pd77%Ag23% Membranes

Sputtered Pd77%Ag23% membranes of thickness 2.2–8.5 µm were subjected to a three-step heat treatment in air (HTA) to investigate the relation between thickness and the reported beneficial effects of HTA on hydrogen transport. The permeability experiments were complimented by volumetric hydrogen sorption measurements and atomic force microscopy (AFM) imaging in order to relate the observed effects to changes in hydrogen solubility and/or structure. The results show that the HTA—essentially an oxidation-reduction cycle—mainly affects the thinner membranes, with the hydrogen flux increasing stepwise upon HTA of each membrane side. The hydrogen solubility is found to remain constant upon HTA, and the change must therefore be attributed to improved transport kinetics. The HTA procedure appears to shift the transition from the surface to bulk-limited transport to lower thickness, roughly from ~5 to ≤2.2 µm under the conditions applied here. Although the surface topography results indicate that HTA influences the surface roughness and increases the effective membrane surface area, this cannot be the sole explanation for the observed hydrogen flux increase. This is because considerable surface roughening occurs during hydrogen permeation (no HTA) as well, but not accompanied by the same hydrogen flux enhancement. The latter effect is particularly pronounced for thinner membranes, implying that the structural changes may be dependent on the magnitude of the hydrogen flux.