Electric Power and Syngas from Methane—An Energy-Efficient Combination of a Single-Chamber Fuel Cell and Downstream Catalytic Equilibration

摘要

The high-temperature solid oxide fuel cell (SOFC) is known for its stability and high efficiency. In contrast to many other fuel cells SOFCs not only tolerate but utilize even CO, such that the oxidation of H2 as well as CO can be used to generate electric power. For this reason, in conventional SOCFs an upstream reformer usually converts methanol or hydrocarbons with water, CO2, or O2 to a mixture containing H2 and CO for electrocatalytic oxidation. Problems in this approach include coking of the anode, resulting from the feed-gas separation required for the double-chamber configuration of conventional SOFCs, and the incomplete conversion in the reformer and the electrochemical oxidation. The selective oxidation of methane to CO and 2H2 (syngas) is exothermic with an enthalpy of about 36 kJmol~(-1). This heat of reaction is not enough for the efficient generation of thermal energy because the temperature gradients are too small, but it is high enough to result in potential hot-spot formation and to raise reactor safety issues. In addition, the thermodynamic driving force requires temperatures above 800 °C for the selective formation of syngas. The partial oxidation of methane (POM) and oxygen to syngas has been the subject of intensive studies during the last 10 years. Typical catalysts are based on nickel and cobalt, where the former tends to coking and the latter tends to deactivation. There are many approaches to improve the catalytic properties by doping, especially with rare-earth elements.