Experimental and Modeling Investigation of CO3=/OH\u2013 Equilibrium Effects on Molten Carbonate Fuel Cell Performance in Carbon Capture Applications

Molten Carbonate Fuel Cells (MCFCs) are used today commercially for power production. More recently they have also been considered for carbon capture from industrial and power generation CO2 sources. In this newer application context, our recent studies have shown that at low CO2/H2O cathode gas ratios, water supplements CO2 in the electrochemical process to generate power but not capture CO2. We now report the direct Raman observation of the underlying carbonate-hydroxide equilibrium in an alkali carbonate eutectic near MCFC operating conditions. Our improved electrochemical model built on the experimental equilibrium data adjusts the internal resistance terms and has improved the representation of the MCFC performance. This fundamentally improved model now also includes the temperature dependence of cell performance. It has been validated on experimental data collected in single cell tests. The average error in the simulated voltage is less than 4% even when extreme operating conditions of low CO2 concentration and high current density data are included. With the improvements, this electrochemical model is suitable for simulating industrial cells and stacks employed in a wide variety of carbon capture applications

The Effects of Gas Diffusion in Molten Carbonate Fuel Cells Working as Carbon Capture Devices

Molten Carbonate Fuel Cells (MCFCs) are used in MW-scale power plants. Recently, they have also been explored for carbon capture. A recent MCFC experimental campaign for carbon capture applications has shown interesting results. It revealed that at carbon capture conditions a secondary reaction mechanism involving hydroxide ions starts to affect cell performance. This is important since part of the electricity produced will be used to transfer water instead of CO2, decreasing capture efficiency. Previously, the authors developed a dual-ion model for MCFCs to account for the observed loss of carbon capture efficiency at low-CO2 cathode gas conditions. A more recent, deeper exploration of MCFC control parameters found that the split between the competing reaction paths depends not only on the cathode gas composition, but also on cathode diffusion resistance. Thus, in this work we increase the applicability range and reliability of the dual-ion electrochemical model by including the diffusion of reactants in the porous cathode along the axis perpendicular to the cell plane. This transport component can account for the shifting of carbonate and hydroxide contributions to the overall cell current as a function of cathode feed properties and for different current collector designs that determine the diffusion resistance term