Brentan R. Alexander

Steam-Carbon Fuel Cell Concept for Cogeneration of Hydrogen and Electrical Power

This study describes and presents the results of a new electrochemical approach to co-production of hydrogen and electric power using a steam-carbon fuel cell, within which carbon-containing species are kept physically separate from the hydrogen stream by a solid oxide electrolyte membrane. The fuel cell used for this purpose consists of H 2 , H 2 O (g) /Pt/YSZ/Pt/C (s) ,CO,CO 2 and measurements are taken between 600 and 900°C. Peak electrical power generated at 900°C is 8 mW/cm 2 at a current density of 40.5 mA/ cm 2 corresponding to simultaneous production of carbon-free hydrogen at a rate of 354 g H 2 /m 2 day. Electrochemical behavior and cell loss mechanisms are studied using impedance spectroscopy in different cell arrangements operating in steam-carbon and air-carbon modes. Exchange current densities extracted from these measurements indicated activation energies of 80.3 ± 7.9 kJ/ mol for oxygen reduction, 132±12 kJ/mol for CO oxidation, and 189 ± 35 kJ/mol for steam reduction. These results indicate that steam reduction is the dominant loss mechanism with significant contribution from CO oxidation kinetics. Modeling results for the carbon bed indicate that a bed height of 7 mm is capable of supporting cell current densities of 700 mA/cm 2 at 85% effective char utilization, allowing for high performing steam-carbon fuel cells for the simultaneous production of hydrogen and electrical work.

Model of Carbon Utilization in a Solid Carbon Fuel Cell

Introduction The growing global demand and reliance on energy is leading to an increased focus on the environmental issues related to climate change from the carbon emissions produced by energy systems. However, carbon based fuels, such as coal and biomass, will continue to be an important component of the energy balance for the foreseeable future due to their abundant supply and low cost. To utilize carbon sources more efficiently in the production of electricity, thereby proportionally reducing the amount of CO2 generated per unit of electrical output, we have previously proposed and demonstrated an electrochemical conversion approach utilizing a solid carbon fuel cell (SCFC) arrangement[1-4].This cell utilizes solid carbon fuel, coal or biomass, directly in a solid oxide fuel cell (SOFC) to produce electricity. To better understand the SCFC system and evaluate the cell under a variety of conditions, an integrated model of the cell, which includes both the fuel conversion dynamics within the carbon fuel bed as well a model of the fuel cell processes at the electrodes and through the electrolyte, wasdeveloped. This model has been validated and exercised to demonstrate the response of the system, and the design tradeoffs that must be considered when building a SCFC system.