High-Efficiency Reversible Hydroxide Exchange Membrane Fuel Cells

Reversible fuel cells have advantages over rechargeable batteries due to their high energy density, minimal self-discharge, and low cost. Reversible hydroxide exchange membrane fuel cells (HEMFCs) are attractive due to their ability to work with platinum-group-metal (PGM)-free catalysts. HEMFCs and hydroxide exchange membrane electrolyzers (HEMELs) have been separately studied. However, it remains a challenge to integrate the two into a single reversible cell. The major factors that limit the development of unitized reversible HEMFCs are low performance of bifunctional oxygen catalysts, hydroxide membrane stability, hydroxide ion conductivity and water management. Previous research has been focusing on electrolyte-fed HEMELs 1. However, the corrosive alkaline solution presents material compatibility problems and increases the system and balance of plant (BOP) complexity. For example, the presence of alkaline solutions can increase the complexity of the unitized reversible fuel cell system due to adding extra water purging steps during the transition between electrolyzer mode and fuel cell mode. In this study, we have developed a pure water-fed reversible HEMFC which makes it possible to use stainless steel to replace the titanium current collectors commonly used in proton exchange membrane electrolyzers (PEMELs) to reduce the manufacturing cost. We have made tremendously progress to make the HEMFC reversible without the addition of alkaline or bicarbonate electrolyte. This is the first reported reversible HEMFC with the highest round trip efficiency (RTE) at an appreciable current density (48% @ 0.5 A/cm2). The reversible test result is shown in Figure 1. In addition to the initial RTE evaluation, we also achieved promising MEA stability. However, a voltage increase was also observed in the initial stage of the durability test which is presumptively attributed to the ionomer wash-out and catalyst layer restructuring. These challenges have been addressed by innovative electrode design. Acknowledgement: The project is finacially supported by the Department of Energy's HFTO under the Grant DE-EE0008438. Reference: Abbasi, R., Setzler, B. P., Lin, S., Wang, J., Zhao, Y., Xu, H., Pivovar, B., Tian, B., Chen, X., Wu, G., Yan, Y., A Roadmap to Low‐Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers. Mater.2019, 31, 1805876 Figure 1