Seven ways to decouple low-temperature water electrolysis - A comparative review for alternative green hydrogen production

This review provides an overview of alternative, decoupled low-temperature water electrolysis systems for the production of green hydrogen that are currently being researched and developed. The continuous or sequential processes utilise a redox mediator enabling the decoupling of the hydrogen and oxygen evolution reactions spatially and/or in time. The different requirements for the redox mediators and the system characteristics are compared, highlighting the physical and chemical limitations of the individual systems, as well as their respective strengths and potential for further development. This indicates that the advantages of decoupled electrolysis compared to direct electrolysis can go far beyond their impressive high faradaic efficiency and operational safety, even at high hydrogen pressure and operation at low current densities . Consequently, it can be presumed that these systems could become a cost- and energy-efficient technology, thereby establishing themselves as a competitive future technology in a multitude of application scenarios.