Power-Generating Electrochemical Anion Exchange CO2 Separator for Practical AEMFC Application

Abstract

Anion exchange membrane fuel cells (AEMFCs) have been widely touted as a low- cost alternative to existing proton exchange membrane fuel cells. However, one of the limitations of this technology has been the severe performance penalty related to the introduction of CO2 to the cell (typically from air in the cathode feed). A low cost, low energy solution is needed that is able to remove CO2 from the incoming air before it is fed to the AEMFC system.1,2 Many approaches to removing CO2 from the cathode inlet would consume valuable energy and complicate the systems-level balance-of-plant. However, recently3, an electrochemical approach was proposed that i) is able to generate power; and ii) takes advantage of the carbonation phenomena that harms AEMFCs. Such a device can be called an anion exchange CO2 separator (AECS).An AECS operates on the same principles as an AEMFC. H2 is fed to the anode and O2/air is fed to the cathode. As OH- is formed from the oxygen reduction reaction at the cathode, it is converted to carbonates by reaction with carbon dioxide. The carbonates are transported to the anode by migration where they are eventually released as CO2. Ideally, an AECS operates on waste H2 and a high concentration CO2 stream leaves the anode and an air stream devoid of CO2 leaves the cathode. By design, the AECS is smaller than the primary AEMFC. Because carbonates are present, the AECS operates at a lower power density than the AEMFC, but the method has the promise to use waste to generate energy while removing CO2.In this work, the effectiveness of an AECS in lowering the CO2 concentration of an incoming stream of 400ppm air is investigated. Several parameters are changed, including the AECS active area and anode flowrate. The primary focus of these experiments was to develop operating conditions that lead to very low ppm CO2 concentrations leaving the AECS cathode. In addition to showing significant CO2 removal, we also show an AECS that operates with a stable output for over 150 h. Finally, AEMFC operation on AECS-purified industrial air is successfully demonstrated. References Zheng, T. J. Omasta, X. Peng, L. Wang, J. R. Varcoe, S. Pivovar, and W. E. Mustain, Energy Environ. Sci., 12, 2806–2819 (2019).R. Gerhardt, L. M. Pant, H.-S. Shiau, and A. Z. Weber, ECS Trans., 86, 15–24 (2018).Yan, B. Setzler, Y. Zhao, M. S. R. Carbonell, and S. Gottesfeld, U.S. Patent No. 10,811,711. 20 Oct. 2020.