Is Direct Seawater Splitting Realistic with Conventional Electrolyzer Technologies?

Dihydrogen (H2) constitutes a promising energy carrier for transporting part of the world's energy demand and concomitantly for reducing toxic emissions. Water electrolysis powered by renewable energy would provide H2 with a small carbon footprint. To save global fresh water, seawater electrolysis has attracted much attention in recent years, since it represents 96.5% of the Earth's resources and is abundant worldwide. However, seawater's composition is complex, which poses problems for direct seawater splitting. To date, seawater splitting usually requires a two-step process, i.e., purification of seawater using reverse osmosis (RO) which represents 69% of the globally produced desalinated water (Jones et al. Sci. Total Environ. 2019, 657, 1343–1356) and then electrolysis of pure water. This involves two separate processes, resulting in a complex design and significant space requirement for their corresponding equipment. Recently, efforts have been made to use seawater directly for H2 production, and electrolyzers using this water source are being developed. The objective of this review is to describe first the impact of direct seawater splitting on water electrolysis technologies and then to present the most recent innovative approaches to avoid pretreatment with particular emphasis on innovative configurations of well-established industrial electrolyzers and new original approaches. Finally, as a conclusion, we will propose perspectives toward the development of electrolyzers enabling the electrochemical production of H2 from seawater for sustainable development.