(Invited) AEM Water Electrolysis: From Materials to System

Anion exchange membrane water electrolysis (AEMWE) is an electrolysis technology that combines the advantages of alkaline liquid electrolysis (ALE) and proton exchange membrane water electrolysis (PEMWE). Specifically, AEMWE may eliminate or reduce the usage of expensive platinum metal group (PGM) catalysts, like its ALE counterpart, while also able to operate at high current density, non-balanced hydrogen pressure, and under dynamic loads, like PEMWE. However, AEMWE has not gained viability in commercial applications due to multiple challenges. From the materials perspective, both electrodes and membrane need further development. Although the oxygen evolution reaction (OER) catalysts for the anode have been studied at a rotating disk electrode (RDE) level for decades, seeing massive improvement in activities, their applications in the real working AEMWE still needs improvement. One challenge that has not been sufficiently addressed is poor adhesion between the substrate and the catalyst coating, which may fall off due to the force of bubbles formed on the surface of electrodes. While many different catalyst coating methodologies have been tried, the pore size and microstructure of the substrates plays an essential role for the quality of the coating and thus the electrode's stability. In addition, the membrane also has some unsolved problems like poor mechanical strength and chemical stability that compromises the longevity of the electrolyzer. It was also found that the interface between the membrane and electrode is crucial to the long durability of the AEMWE. One solution to this is the development of thermally processable AEMs, which can not only elevate the electrolyzer operating temperatures, but also form a better electrode/membrane interface. From the system point of view, the stack build needs to consider frames, sealing, pressure vessel, manifold, and shunt current, particularly when the AEMWE operates with the addition of electrolyte (e.g., KOH). Increasing the efficiency of the stack requires minimizing the shunt current, which is affected by the concentration of KOH, the manifold design, and the number of cells in a stack. Lowering electrolyte concentration is instrumental for reducing the shunt current but can be detrimental for the electrolyzer performance. Engineering solutions, such as using an extremal manifold design can tremendously reduce the shunt current, allowing for higher concentration of electrolyte and better performance. Finally, the successful non-balanced pressure operation (up to 50 bar) is not only determined by the membrane strength, but also the morphology of the supporting substrates like porous transport layers and the quality of assembly. These concepts will be validated in our 50 kW AEMWE stack and inform our 1 MW AEMWE design.