Insights into Carbonate Fuel Cell Operation Under Carbon Dioxide Capture Conditions

Abstract

Providing for increasing global energy needs while managing carbon dioxide emissions is the dual energy challenge the modern world faces. In order to meet this challenge, reliable and dispatchable low carbon energy sources are a likely component. For many scenarios, this suggests that cost effective carbon dioxide capture will be a key technology.[1] Carbon capture with carbonate fuel cells (CFCs) may be one such technology option.[2]Carbonate fuel cells concentrate carbon dioxide from the cathode to the anode as part of their normal operation, effectively doing both carbon capture and low carbon power generation in a single process. (see Figure 1) When generating power, typical carbon dioxide concentrations fed to the CFC cathode tend to be higher than carbon dioxide emissions of many industrial processes. This means that if we want to capture that carbon dioxide, we need the fuel cell to operate at lower carbon dioxide concentrations than it typically does. For carbon capture operations, cathode inlet carbon dioxide concentrations could be as low as 4%. Additionally, under typical power generation operations, CFCs only capture a fraction of the carbon dioxide (<50%) fed to the cathode, where for carbon capture rates may be as high as 90%. Together these two constraints (low initial concentration and higher capture) results in very low carbon dioxide concentrations in the cell, particularly at the cathode outlet. This may impact the fundamental chemistry of the process. Carbon dioxide capture at 4% and lower was tested in a fuel cell, specifically designed to minimize mass transport effects external to the active cell components. Carbon capture was demonstrated at a range of carbon dioxide concentrations ranging from standard operation for power generation (>10%) to <1%. Additionally, oxygen concentrations and current densities were varied over likely operational ranges. We demonstrate that under most circumstances, operations under carbon capture conditions proceed via a similar mechanism to those under power generation conditions. However, in harsh or extreme conditions, where carbon dioxide concentrations are low (<0.5%) and/or current densities high, alternative mechanisms appear. We demonstrate how the CFC performs when these alternative mechanisms are present. Additionally, our findings suggest that they appear to utilize water in place of carbon dioxide and allow the cell to operate at conditions beyond theoretical complete carbon capture. [1] IEA World Energy Outlook 2018; Bloomberg New Energy Finance, New Energy Outlook 2018 [2] Ghezel-Ayagh H., Jolly S., Patel D., Hunt J., Steen W., Richardson C., Marina O., (2013) A Novel System for Carbon Dioxide Capture Utilizing Electrochemical Membrane Technology ECS Transaction Vol 51 (1) 265-272 Figure 1