UNDERSTANDING DIRECT BOROHYDRIDE - HYDROGEN PEROXIDE FUEL CELL PERFORMANCE

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dc.contributor.advisorJackson, Gregory Sen_US
dc.contributor.authorStroman, Richard O'Neilen_US
dc.contributor.departmentMechanical Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2014-02-06T06:30:08Z
dc.date.available2014-02-06T06:30:08Z
dc.date.issued2013en_US
dc.description.abstractDirect borohydride fuel cells (DBFCs) generate electrical power by oxidizing aqueous BH<sub>4</sub><super>-</super> at the anode and reducing an oxidizer, like aqueous H<sub>2</sub>O<sub>2</sub> for an all-liquid fuel cell, at the cathode. Interest in DBFCs has grown due to high theoretical energy densities of the reactants, yet DBFC technology faces challenges such as side reactions and other processes that reduce cell efficiency and power generation. Relationships linking performance to cell design and operation will benefit from detailed and calibrated cell design models, and this study presents the development and calibration of a 2D, single-cell DBFC model that includes transport in reactant channels and complex charge transfer reactions at each electrode. Initial modeling was performed assuming ideal reactions without undesirable side reactions. Results were valuable for showing how design parameters impact ideal performance limits and DBFC cell voltage (efficiency). Model results showed that concentration boundary layers in the reactant flow channels limit power density and single-pass reactant utilization. Shallower channels and recirculation improve utilization, but at the expense of lower cell voltage and power per unit membrane area. Reactant coulombic efficiency grows with decreasing inlet reactant concentration, reactant flow rate and cell potential, as the relative reaction rates at each electrode shift to favor charge transfer reactions. To incorporate more realistic reaction mechanisms into the model, experiments in a single cell DBFC were performed to guide reaction mechanism selection by showing which processes were important to capture. Kinetic parameters for both electrochemical and critical heterogeneous reactions at each electrode were subsequently fitted to the measurements. Single-cell experiments showed that undesirable side reactions identified by gas production were reduced with lower reactant concentration and higher supporting electrolyte concentration and these results provided the basis for calibrating multi-step kinetic mechanism. Model results with the resulting calibrated mechanism showed that cell thermodynamic efficiency falls with cell voltage while coulombic utilization rises, yielding a maximum overall efficiency operating point. For this DBFC, maximum overall efficiency coincides with maximum power density, suggesting the existence of preferred operating point for a given geometry and operating conditions.en_US
dc.identifier.urihttp://hdl.handle.net/1903/14823
dc.language.isoenen_US
dc.subject.pqcontrolledMechanical engineeringen_US
dc.subject.pqcontrolledChemical engineeringen_US
dc.subject.pqcontrolledAlternative energyen_US
dc.subject.pquncontrolledborohydrideen_US
dc.subject.pquncontrolleddesignen_US
dc.subject.pquncontrolleddirecten_US
dc.subject.pquncontrolledexperimenten_US
dc.subject.pquncontrolledfuel cellen_US
dc.subject.pquncontrolledmodelen_US
dc.titleUNDERSTANDING DIRECT BOROHYDRIDE - HYDROGEN PEROXIDE FUEL CELL PERFORMANCEen_US
dc.typeDissertationen_US

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