Composite Anion Exchange Membranes with Quaternized Graphene Oxide for Water Electrolyzer Applications

Alkaline technology, alongside proton exchange membrane (PEM) electrolysis, constitutes one of the two primary low-temperature operation methods, spanning from room temperature up to 80°C. However, conventional alkaline technology faces limitations in renewable electricity storage due to poor performance and compatibility issues with intermittent operations, attributed to factors like large inter-electrode distances and the absence of a membrane separator. While alkaline water electrolyzers (AWEs) are surpassed by proton exchange membrane water electrolyzers (PEMWEs) in efficiency, PEMWEs suffer from durability issues and higher costs due to the use of PEMs like Nafion and Platinum Group Metal (PGM)-based catalysts. An emerging alternative, the polymer-based Anion Exchange Membrane Water Electrolyzer (AEMWE), holds promise by employing non-precious metal catalysts (NPMC) and less expensive membranes, aiming to combine the resilience of AWEs with the performance of PEMWEs in less corrosive environments. However, the poor hydroxide ion (OH−) conductivity compared to protons (H+), as well as thermal and chemical stability, pose significant challenges in the development of anion exchange membranes (AEMs) [1]. To address these challenges, this study first incorporated varying amounts of Graphene Oxide (GO), synthesized via a modified Hummers method [2], into the Fumion® FAA-3 ionomer (10% w/w in NMP) using the solvent casting technique to fabricate AEMs. Then, after proving the beneficial effect of GO on the conductivity and stability of the AEMs [3], the GO was functionalized with quaternary ammonium groups using three simple and innovative synthesis methods (the obtained products were named QGO1, QGO2 and QGO3), in order to further increase the conductivity of the AEMs. The resulting composite membranes (containing 1%wt of additive respect to the polymer) shown a high conductivity, more than 100 mS/cm at 60°C for the most performing one, respect to 55 mS/cm at 60°C of the benchmark membrane without additive.