Recent developments on transition metal–based electrocatalysts for application in anion exchange membrane water electrolysis

Anion exchange membrane water electrolyzer (AEMWE) is a promising technology in water electrolysis for the production of green hydrogen. Unlike conventional alkaline water electrolyzers (AWE), AEMWEs utilize mild alkaline conditions and anion exchange membranes as separators and ionic conductors, respectively. However, the largest merit of AEMWE is the utilization of low-cost transition metals as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Achieving excellent AEMWE performance using highly active and robust transition metal electrocatalysts is desired for lowering the fabrication cost and realizing the successful commercialization of AEMWE. Water splitting efficiency in the AEMWE largely depends on the kinetics of the HER and OER catalysts. Such a condition requires proper understanding of the reaction mechanisms, careful design and optimization of catalyst materials, and maintenance of catalyst durability under AEMWE conditions during long-term operation. This review discussed recent transition metal HER, OER, and bifunctional water splitting electrocatalysts applied within the actual AEMWE membrane electrode assembly (MEA), where their influence toward the electrolyzer cell performance is highlighted. Additionally, the MEA fabrication methods are briefly addressed. From the review, potential electrocatalyst materials and remaining challenges are identified to provide for future improvements on the AEMWE system.