Anion Exchange Membrane Water Electrolysis: The Future of Green Hydrogen

Abstract

Hydrogen-derived power is one of the most promising components of a fossil fuel-independent future when deployed with green and renewable primary energy sources. Energy from the sun, wind, waves/tidal, and other emissions-free sources can power water electrolyzers (WEs), devices that can produce green hydrogen without carbon emissions. According to recent International Renewable Energy Agency reports, most WEs employed in the industry are currently alkaline water electrolyzers and proton-exchange membrane water electrolyzers (PEMWEs), with ∼200 and ∼70 years of commercialization history, respectively. The former suffers from inherently limited current densities due to inevitable gas crossover, operates using corrosive (7 M) alkaline solutions, and requires large installation footprints, while the latter requires expensive and scarce precious metal-based electrocatalysts. An emerging technology, the anion-exchange membrane water electrolyzer (AEMWE), seeks to combine the benefits of both into one device while overcoming the limitations of each. AEMWEs afford higher operating current densities and pressures, similar Faradaic efficiencies when compared to PEMWEs (>90%), rapid ramping/load-following responsiveness, and the use of non-noble metal catalysts and pure water feed. While recent reports show promising device performance, close to 3 A/cm2 for AEMWEs with 1 M KOH or pure water feed, a deeper understanding of the mechanisms that govern device performance and stability is required for the technology to compete and flourish. Herein, we briefly discuss the fundamentals of AEMWEs in terms of device components, catalysts, membranes, and long-term stability/durability. We provide our perspective on where the field is going and offer our opinion on how specific performance and stability tests should be performed to facilitate the development of the field.