Experimental and Numerical Analysis of Alkaline Exchange Membrane Water Electrolyzers
Authors: Eitzen Jasper , Mouallem Jake , Storbakken Scott , Quintero Andrea , Secanell Marc 
Published: December 2024

The operation of fuel cells and electrolyzers in alkaline conditions allows for the use of: i) less expensive electrocatalyst, such as nickel alloys and silver, ii) cheaper metals for porous layers and bipolar plates due to the less corrosive environment at high pH, e.g., nickel and stainless steel compared to titanium in PEMWE; and, iii) seawater for electrolysis [1]. However, it is only in the past decade that remarkable strides in polymer synthesis and stabilization techniques have enabled the fabrication of AEMs and ionomers that are stable at high pH and above 80oC, and have ionic conductivities as high as the standard PEM materials. Currently, several commercial AEMs and ionomers are available, e.g., Ionomr Aemion (hexamethyl-p-terphenyl poly(benzimidazolium)), Versogen and Sustanion. AEMWEs have demonstrated remarkable power and current densities, e.g., 2 A/cm2 at 1.8 V using 1 M KOH [2] and and 1 A/cm2 at 1.8 V using pure water and PGM-free catalysts [3]. Molero-Gonzalez et al. [4] also demonstrated AEMWE degradation rates of 13 μV/h over 8,900 h at a current density of 600 mA cm−2. Research however is still needed for the development of AEMWE with low-PGM and PGM-free electrodes that are able to operate over a wide range of operating conditions, e.g., alkalinity, temperature, pressure and low flow rate and with high durability. The development of these systems necessitates research and development in the areas of electrode fabrication, characterization, testing and numerical simulation to highlight the most critical limiting kinetic and transport processes in a wide range of available AEMs and catalysts.

In this presentation, catalyst coated membranes (CCMs) fabricated in-house by inkjet printing using platinum and iridium as the cathode and anode catalysts onto reinforced Aemion+ membranes are assessed for their performance under a variety of feed methods. Three possible feed configurations are investigated: two-electrode feed, anode-only feed, and cathode-only feed, using a 1 M KOH solution as feedstock. These CCMs resulted in a performance of 0.9 A/cm2 at 2 V in two-electrode and anode-only feed configurations, but under cathode-only feed, the performance decreased to 0.55 A/cm2 at 2 V, as shown in the figure. Therefore, supplying electrolyte only to the anode does not lead to any performance penalties and eliminates the need for a gas separation unit. Short-term stability was also acceptable for anode-only and two-electrode feed but suffered under cathode-only feed. This performance disparity was not caused by an increase in membrane resistance, as the measured high frequency resistance did not change significantly. A reference electrode was integrated into the cell hardware to investigate the reasons for the difference in performance, finding that the poor cathode-only feed performance was largely caused by an increase in the anode overpotential. A two-dimensional AEMWE model was also developed to further analyze experimental results, and study ion and reaction distribution in each electrode, as well as the sensitivity of AEMWE performance on KOH concentration.

Reference

[1] Du et al. Chemical Reviews, 122 (13):11169-11896, 2022.

[2] Fortin et al. Journal of Power Sources, 451:227814, 2020.

[3] Li et al., Nature Energy, 5:378-385, 2020.

[4] Molero-Gonzalez et al. Journal of Power Sources Advances 19:100109, 2023.

Figure 1