Enhancing Oxygen Exchange Activity by Tailoring Perovskite Surfaces.

A detailed understanding of the effects of surface chemical and geometric composition is essential for understanding the electrochemical performance of the perovskite (ABO3) oxides commonly used as electrocatalysts in the cathodes of ceramic fuel cells. Herein, we report how the addition of submonolayer quantities of A- and B-site cations affects the rate of the oxygen reduction reaction (ORR) of Sr-doped LaFeO3 (LSF), LaMnO3 (LSM), and LaCoO3 (LSCo). Density functional theory calculations were performed to determine the stability of different active sites on a collection of surfaces. With LSF and LSM, rates for the ORR are significantly higher on the A-site terminated surface, while surface termination is less important for LSCo. Our findings highlight the importance of tailoring the surface termination of the perovskite to obtain its ultimate ORR performance.

Simplified Modeling of Organic Contaminant Adsorption by Activated Carbon and Biochar in the Presence of Dissolved Organic Matter and Other Competing Adsorbates.

Cyclohexanol, phenol, benzoic acid, and phenanthrene fractional removal (italicized words are defined within the main text) by pulverized granular activated carbon and biochar adsorption in deionized water and stormwater was independent of target-adsorbate initial concentrations (C0) when C0s were below concentration thresholds. This permits a simple-modeling approach. C0-independent removal in deionized water at low-target-adsorbate concentrations potentially suggests that DOM in the deionized water induce a competitive effect that causes deviations from the Freundlich model. The Ideal Adsorbed Solution Theory-Equivalent Background Compound model was used to determine the magnitude of concentration thresholds and the competitive effect of stormwater DOM and possibly deionized water DOM. These competing substances' competitive effects were influenced by target-compound adsorbability and structure. Concentration thresholds positively correlate with competing substances' competitive effect and negatively correlate with target-adsorbate-Freundlich 1/n values. In deionized water, concentration thresholds increase as target-compound adsorbability decreases. In stormwater, concentration thresholds do not correlate with adsorbability, potentially because stormwater DOM is better suited to compete for aromatic-compound-adsorption sites. The extent known-competitor adsorbates decrease target-adsorbate removal in the presence of DOM is investigated, which depends on the competing adsorbates' relative adsorbabilities and if they adsorb to a different subpopulation of adsorption sites.