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Concentration polarization is important because it determines the maximum power output of a solid oxide fuel cell (SOFC) at high fuel utilization. Anodic concentration polarization occurs when the demand for reactants exceeds the capacity of the porous cermet anode to supply them by gas diffusion mechanisms. High tortuosities (bulk diffusion resistances) are often assumed to explain this behavior. However, recent experiments show that anodic concentration polarization originates in the immediate vicinity of the reactive triple phase boundary (TPB) sites near the anode/electrolyte interface. A model is proposed to describe how concentration polarization is controlled by two localized phenomena: competetive adsorption of reactants in areas adjacent to the reactive TPB sites, followed by relatively slow surface diffusion to the reactive sites. Results suggest that future SOFC anode design improvements should focus on optimization of the reactive area, adsorption, and surface diffusion at the anode/electrolyte interface. © 2003 The Electrochemical Society. All rights reserved.

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The Department of Energy Bioenergy Technologies Office (BETO) invests in research and development of new pathways for commercially viable conversion of biomass into drop-in ready transportation fuels, fuel blendstocks and products. The primary emphasis has been on terrestrial and algae feedstocks, but more recently BETO has begun to explore the potential of wet wastes for biofuel production, with focus on wastewater residuals, manure, food waste, and fats, oils and grease. A recent resource analysis estimates that 77 million dry tons per year of these wastes are generated annually, 65% of which are underutilized for any beneficial purpose. 1 Approximately 14 million dry tons of the total resource is wastewater residuals (sludge and biosolids) generated at the nation's wastewater treatment plants (WWTPs). 2 Conversion of this resource into transportation fuels could significantly contribute to the creation of a new domestic bioenergy and bioproduct industry, while providing an economically and environmentally sustainable alternative for current waste disposal practices.