Abstract: Polymer electrolyte membrane (PEM) water electrolysis (or water splitting), including proton exchange membrane water electrolysis, anion exchange membrane water electrolysis, and bipolar polymer electrolyte membrane water electrolysis, can offer numerous advantages, such as a compact and flexible system design, high gas purity, low gas crossover, and the ability to operate at high current densities. However, the current performance and cost of membranes, electrocatalysts, and membrane electrode assemblies remain inadequate to meet the demands of large-scale commercial deployment. Based on the technical principles as well as advantages and disadvantages of PEM water electrolysis, this paper provides a comprehensive and in-depth review of recent progress and advancements in terms of the protonic/anionic/bipolar membranes and degradation mechanisms, noble metal/non-noble metal/metal-free electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and bifunctional applications, as well as membrane electrode assemblies and their design strategies and construction methods. Key technical challenges associated with emerging PEM water electrolysis technologies are analyzed, and prospective research directions to address these challenges are proposed to guide continuous innovation and promote practical implementation towards hydrogen energy generation.

Key words: Water electrolysis/splitting, Hydrogen energy, Polymer electrolyte membranes, Electrocatalysts, Membrane electrode assemblies