Ionomer–catalyst interaction in the catalyst layer for alkaline membrane water electrolysis

Alkaline membrane water electrolysis is gaining attention as a hydrogen production technology combining the advantages of the alkaline and proton exchange membrane water electrolysis. To fully utilize the potential of this technology, it is necessary to prepare a membrane-electrode assembly characterized by high efficiency and intensity of electrolysis. One of the vital demands to achieve this target is the establishment of a frequent triple-phase boundary. If a concentrated liquid electrolyte is used, this boundary occurrence is established due to the ionic conductivity of the electrolyte solution. In the case of a diluted liquid electrolyte, in the ideal case, demineralized water circulating through the cell, this task is accomplished by the interactions between catalyst and ionomer, fulfilling the role of binder and ion conductor. This review focuses on advances in the second approach, namely ionomer design, catalyst layer composition, and the impact of the selected parameters such as catalyst to binder ratio, catalyst load, and type of membrane–electrode assembly.