Rational Design of Membrane Electrode Assembly for Anion Exchange Water Electrolysis

Abstract

In the framework of an increased interest for green hydrogen production, Anion Exchange Membrane Water Electrolysis (AEMWE) systems have attracted tremendous attention. Platinum group metal-free (PGM-free) catalysts can be effectively exploited with this technology to reach higher current densities compared to traditional alkaline electrolysis [1]. However, challenges are posed by the stability of the anion conducting polymer in the membrane and in the catalyst layers (CLs). Furthermore, the scarcity of works showing devices with stable performance which can work without a supporting electrolyte raises the question of whether or not it is possible to rely on ionomer conductivity for CL.Here, we focus on a method for the fabrication of catalyst coated membranes (CCMs). This strategy has the benefit of enhancing the interfacial contact between the CL and the membrane, reducing the cell resistance when low conducting electrolytes or pure water are used. Inspired by the industrial approach for proton exchange membrane (PEM) fuel cell fabrication, we applied the “decal transfer” method to AEMWE. In this approach, the CL is first coated on a substrate and then transferred on the membrane surface to fabricate the so-called MEA. This method is easy to scale up and allows for fine control of catalyst loading.In our work, we investigated the effect of ionomer content on the electrode performance. After optimizing the ionomer weight fraction for both anode and cathode, we studied the stability of MEAs at 200 mA/cm2 in 1 M KOH. It was found that when the anion conducting ionomer (AP-1-HNN8-00-X) in the anode CLs was replaced with Nafion, the electrode performance (Figure 1a) and stability were significantly improved (Figure 1b). Additionally, the electrode utilization was increased due to the higher density and lower water uptake of Nafion which reduces the volume fraction of Nafion in the CL. Reduced electrode resistance was also observed using Nafion when compared to the anion exchange ionomer (figure 1a). Since Nafion is chemically stable and does not suffer from excessive water uptake and dissolution, contrary to anion exchange ionomers [2], it can be easily used as a binder in AEMWE.These findings point out that MEAs for AEMWE can be manufactured with the “decal” method, however, their performance is limited by the catalyst surface area and ionomer stability. These two elements are fundamental towards pure water AEMWE.