Deciphering chlorine-involved electrochemistry and metal dissolution in direct seawater electrolysis

Direct seawater electrolysis (DSWE) is an innovative approach for producing green hydrogen, leveraging the planet's water resources while addressing the challenge of limited freshwater availability. The real-world implementation necessitates addressing numerous fundamental and interrelated challenges, including the dissolution of active metals, corrosion induced by chlorine (Cl − ), catalyst poisoning, and cathodic precipitation. Cl − species hinder the desired oxygen evolution process by promoting the competing chlorine evolution reaction (CIER), which significantly degrades electrode materials and reduces system efficiency and longevity. Encouragingly, this paper explores innovative technical approaches for either separating or mitigating harmful Cl − chemistry, advanced surface modifications to strengthen the long-term stability of DSWE, and strategies for stabilizing active metals. A detailed overview of the fundamentals of Cl − chemistry and corrosion is elucidated. Thus, boosting resistance to corrosive conditions and enhancing selectivity. Besides, novel electrode designs are presented to regulate bubble transport and reduce precipitation. These pertain to highly OER-selective catalyst architectures, corrosion-resistant systems, surface-reconstruction processes, and strategies aimed at addressing cathode fouling through in situ acidification and hydrophobization of the catalyst. During the process, numerous seawater oxidation catalysts experience considerable surface reconstruction, frequently transitioning from the synthetic state to an ecologically active metallic hydroxide layer. The efficiency of DSWE technologies can be enhanced through engineering various electrolytes, including buffer ions and inhibitors. Subsequently, we examine various electrolyzer topologies, membrane strategies (e.g., non-ion-exchange membranes and ion-exchange membranes), flow systems, and potential pulse electrolysis techniques that facilitate the dynamic reduction of Cl − interference and a corrosive environment. Additionally, we conduct a comprehensive assessment of the operando characterization tools employed in DSWE to emphasize their function in facilitating direct monitoring of oxidation states, intermediate generation, surface adsorbate dynamics, and charge transfer under electrochemical working conditions. In conclusion, we outline the significant challenges, perspectives and opportunities that necessitate focus in the future advancement of DSWE technologies. This review aims to elucidate and pinpoint viable options for comprehensive research and technological applications of durable DSWE-based hydrogen production by merging fundamental electrochemical concepts with system-level analyses.