A Review of Designing Hierarchical Structure Within Membrane Electrode Assembly for Water Electrolyzer

Green hydrogen produced from water electrolyzers demonstrates higher efficiency and sustainability than industrial alkaline water electrolysis due to the membrane electrode assembly (MEA) design. However, random structure designs in current MEAs significantly increase the charge and mass transport resistance, leading to a decrease in energy efficiency. In contrast, the ordered structure design in MEA provides well-defined arrangements of pores, channels, or pathways within catalysts, catalyst layers, porous transport layers, and ion exchange membranes (IEMs). These ordered configurations facilitate efficient pathways for charge and mass transport. Particularly, in comparison with first-order structure, hierarchical structure designs exhibit more obvious advantages in reaction interface, charge, and mass transport. Recently, the diverse hierarchical structure in the MEA designs has demonstrated significant improvements in overall electrolysis efficiency in both proton exchange membrane (PEM) and anion exchange membrane (AEM) water electrolyzers. This review will examine recent advancements in hierarchical structure designs in the MEAs for water electrolyzers, focusing on innovations in fabrication methods and enhancement mechanisms, as well as their electrolysis performance. This review will provide comprehensive guidelines for designing highly efficient MEAs for both PEM and AEM electrolyzers.