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, H2O(g)/Pt/YSZ/Pt/C-(s), CO, CO2 and measurements are taken between 600 and 900 degrees C. Peak electrical power generated at 900 degrees 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. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3560475] All rights reserved.