The ARPA-E Ionics Program: Advancing Anion Exchange Membranes

Abstract

In 2016 ARPA-E launched the IONICS (Integration and Optimization of Novel Ion-Conducing Solids) program, motivated by the enabling role of separator technology and the remaining performance and cost gaps across multiple types of electrochemical devices. The 16 teams in the IONICS program are focused on developing breakthrough separators that would be broadly enabling in different areas of electrochemical technology, and also amenable to cost effective manufacturing. The projects include both polymer and inorganic ion conducting separators that enable electrode chemistries that have been previously unsuccessful in practical devices. Project teams are focused on overcoming property tradeoffs to achieve a full set of required attributes, including conductivity, selectivity, stability, mechanical properties, manufacturability, cost, and others. This contrasts with a common approach of optimizing a single variable at the expense of others. The IONICS focus is on solids rather than liquids, due to inherent advantages in selectivity and mechanical properties offered by solids. The IONICS program is focused on three areas: (1) Li+ conductors that enable the cycling of the lithium metal electrode at conditions required for high-energy cells, (2) highly selective polymer separators for flow batteries, and (3) anion-conducting polymer separators for use in alkaline fuel cells, electrolyzers, and other electrochemical devices. This talk will focus on area (3), where the potential benefits of the alkaline environment include the reduction/elimination of platinum-group metal catalysts for both hydrogen and oxygen electrodes, and the ability to use lower cost, uncoated, stainless steel plates. The polymer attributes pursued in the program include extended stability (1,000 h with negligible degradation) in alkaline conditions at a temperature of 80°C or higher, low area-specific ionic resistance (<=0.04 ohm-cm2 in liquid form), limited swelling (<50%), and low cost (<=20 $/m2). Additionally, fuel cell applications require the membrane to retain high conductivity under air exposure and avoid degradation during humidity cycling, while electrolysis applications require it to withstand a differential pressure of tens of bar. A key limitation for the development of improved membranes in this growing field is the lack of specific, consistent test conditions, which makes it difficult to easily identify the most promising membranes. This talk will outline the test conditions developed for the IONICS program teams, which we hope will be used by other research groups to advance progress in this important field.