Daniel Konopka

Composition- and Morphology-Dependent Corrosion Stability of Ruthenium Oxide Materials

Ruthenium oxide materials were evaluated as possible non-carbon-based supports for fuel cell catalysts. The effects of composition and morphology of ruthenium oxide materials on the conductivity and corrosion stability in the gas-diffusion electrode (GDE) configuration were thoroughly investigated. The compositions of the bulk and surface of three ruthenium oxide materials, along with the surface area and surface morphology, were compared. We have found that all tested ruthenium oxide powders exhibited higher corrosion stability compared to carbon. Full conversion of RuO(2).nH(2)O to the RuO(2) phase by postreduction in a hydrogen atmosphere leads to improved conductivity and corrosion stability.

Functional DMFC Cathode Catalysts and Supports Based on Niobium Oxide Phase

Composite electrocatalysts consisting of platinum nanophase supported on carbon black decorated with niobium oxide phase were prepared by a two step precipitation/reduction procedure. The intrinsic catalytic activity of these materials was evaluated for the oxygen electroreduction reaction, measured in the absence and presence of methanol. It was found that the Nb x O y -composite materials are more hydrophilic and thus initially have lower intrinsic catalytic activity for oxygen reduction. However, materials containing Nb x Oy offer better overall platinum mass utilization, achieved through much better dispersion of the platinum nanophase. Such advantageous dispersion is observed even for high metal loadings. Another advantage of these materials is minimal effect of poisoning with the intermediates formed during methanol oxidation that results in the enhanced methanol tolerance in direct methanol fuel cells (DMFC). .

Electrochemical and DFT Analysis of Deactivation of Pt Supported on Niobia

The catalytic deactivation of platinum supported on NbRuyOz mixed metal oxide support has been investigated. 60% Pt/NbRuyOz was synthesized in a single step using spray pyrolysis, followed by reductive thermal post-treatment. The catalyst was deposited onto a tabbed, Au TEM grid and rapidly cycled between anodic and cathodic potentials in 0.1M HClO4 and 1M KOH to observe mechanisms of corrosion and deactivation. After 3600 cycles, TEM shows a thin film of oxygen-rich niobia with the potential to block ion transport covering the catalyst and support particles. Density Functional Theory calculations indicate that the rate of oxygen diffusion across the Pt(111) surface is in good agreement with experimental observations of the period of catalyst deactivation (several weeks) when exposed to open atmosphere. This suggests that the mechanism of catalytic deactivation could involve the capture and release of oxygen as Nb2O5 breaks down into reduced fragments of NbOx.