Effect of Carbon Capture Endurance Conditions on Performance and Stability of Molten Carbonate Fuel Cell Cathode Electrode

Introduction The molten carbonate fuel cell (MCFC) is one of the most advanced high-temperature and clean power generating devices. To date >8 billion kWh of electricity has been produced commercially using this new technology. The high operating temperature of MCFC (550-650 °C) dramatically improves the reaction kinetics and eliminates the need for a noble metal catalyst. The electrochemical reactions taking place during cell operation involve the CO2 transfer from cathode to anode in the form of carbonate ions (Figure 1). Therefore, MCFC stack technology can be used for power generation and simultaneously, as an effective CO2 separator. MCFC systems can be combined with conventional combustion-powered generators (coal and/or natural gas based power plants) to efficiently separate CO2 in the exhaust gas and produce additional electricity. The state of the art MCFC cathode is porous lithiated nickel oxide. The cathode stability and performance are affected by several factors such as gas composition, temperature, electrode structure and electrolyte chemistry. To ensure long-term performance and material stability against NiO dissolution, polarization loss, and carbon capture efficiency, major considerations need to be taken into account in material selection, operating conditions, and electrode structure design. FCE has tested many single cells (250 cm2) and technology stacks (30 kW) under carbon capture operating conditions (4-5% CO2 in the cathode inlet as opposed to >15% in baseline MCFC systems) to understand parameters affecting performance, life, and to investigate design solutions for further enhancement. Figure 2 highlights the effect of CO2 concentration on the cathode lithiation. These measurements were conducted using an out-of-cell test (OCT) where cathode samples were exposed to different oxidizing environments. It appears that lean-CO2 gas atmospheres (<5%CO2) lead to increased lithium content in the NiO cathode. This may impact the electrolyte distribution and the cathode microstructure. Therefore, the electrolyte inventory (fill level), the lithium content and the basicity need to be considered to achieving optimal operating conditions. This paper will review the cathode material stability, microstructure, and durability under long-term carbon-capture operations. The effect of parameters such as electrolyte fill, gas composition, and electrolyte chemistry, as well as approaches to enhance the CO2 capture efficiency and life, will be discussed. Figure 1