Practical ex-Situ Technique To Measure the Chemical Stability of Anion-Exchange Membranes under Conditions Simulating the Fuel Cell Environment

Abstract

Anion-exchange membrane (AEM) degradation during fuel cell operation represents the main challenge that hampers the implementation of AEM fuel cells (AEMFCs). Reported degradation values of AEMs are difficult to reproduce as no standard methods are used. The present use of different techniques based on exposure of membranes to aqueous KOH solutions under different conditions and measuring different outputs during time does not allow for a reliable and meaningful comparison of reported degradation data of different AEMs. In this study, we present a practical and reproducible ex-situ technique to measure AEM degradation in conditions that mimic an operando fuel cell environment. In this novel technique, we measure the change of the true hydroxide conductivity of the AEM over time, while exposing it to different relative humidity conditions. The technique does not make use of liquid alkaline solution, thus simulating real fuel cell conditions and providing a good baseline for comparative degradation studies.

Overview: State-of-the Art Commercial Membranes for Anion Exchange Membrane Water Electrolysis

“…High hydroxide concentrations are reached, when the membrane is not fully humidified, or when the solution in which the membrane is immersed has a high hydroxide concentration. The driving forces for the accelerated degradation are that (a) hydroxide ions are less well solvated, and therefore more "naked," aggressive nucleophiles at low levels of humidification [28] and that (b) AEMs are not perfect single ion conductors but absorb also potassium ions and excess hydroxide ions when immersed in a KOH solution [18], increasing the number of reactive ions in the membrane. Furthermore, an increasing ion concentration in the outside solution (e.g., the feed solution) affects the osmotic pressure, which reduces the water absorption per absorbed hydroxide ion.…”

Conductivity and Stability Properties of Anion Exchange Membranes: Cation Effect and Backbone Effect

“…[36,37] Water is the medium for transporting OH À , and the values of both IC and chemical stability are correlated with AEMs WU. [38,39] Besides, the cathodic oxygen reduction reaction in AEMFCs requires the participation of water, and WU of AEMs plays an important role in affecting the performance of AEMFCs. [40,41] Therefore, to eliminate the influence of IEC on SD and WU, the AEMs with similar IEC values are prepared.…”

Bifunctional Oxygen Electrocatalysis on Mixed Metal Phthalocyanine-Modified Carbon Nanotubes Prepared via Pyrolysis

“… 46 Due to the fact that these cells allow the application of non-precious-metal catalyst materials, AEMFCs have many other benefits over proton-exchange membrane fuel cells (PEMFCs), including but not limited to a wide choice of fuels and faster ORR kinetics. 47 − 49 The main drawback for AEMFCs was poor conductivity of the anion-exchange membranes (AEMs); however, in recent studies, there are reports on AEMs exhibiting high hydroxide conductivity, 50 − 55 sometimes exceeding 200 mS cm –1 , significantly higher than the proton-conducting Nafion-based membranes. 56 , 57 With the development of highly conducting AEMs, we need suitable catalysts for the enhancement of AEMFC performance.…”