Advances in protective coatings for porous transport layers in proton exchange membrane water electrolyzers: Performance and durability insights

Proton exchange membrane water electrolyzers offer a promising pathway for sustainable hydrogen production. However, the high cost and limited durability of key components, particularly porous transport layers, hinder their widespread adoption. The porous transport layer enables water and electron transport and oxygen removal. Titanium typically enables the required durability, yet the oxidative conditions lower its electrical conductivity. Protective coatings on porous transport layers play a pivotal role in enhancing electrochemical performance and durability by mitigating interfacial contact resistance and maintaining structural integrity under harsh oxidative conditions. This Review highlights the critical impact of porous transport layer coatings on the electrochemical performance and durability by comparing various porous transport layer coatings, including precious metals, non-precious metals, and their combinations. It clarifies the desirable coating material specifications, along with the appropriate morphological, structural, and physical characteristics of the resulting porous transport layers. It also provides a detailed comparative analysis of polarization characteristics, electrochemical impedance responses, potentiostatic and potentiodynamic polarizations, and interfacial contact resistances for various porous transport layer coatings. This Review overviews coating materials and highlights the promising candidates to be considered in the design of next-generation porous transport layers for proton exchange membrane water electrolyzers. The Review assesses the porous transport layer materials from various aspects, including performance, durability, and scalability – all centered around practicality. The Review concludes with the recent progress, remaining challenges, and future research directions.