Perspective on direct seawater electrolysis and electrodesalination: Innovations and future directions for mining Green X

Abstract

Molecular hydrogen (H2) represents a sustainable and environmentally benign energy resource. Of the various methodologies that have been developed for H2 production, water electrolysis has garnered particular attention due to its ability to generate H2 without emitting CO2 or other pollutants, with seawater electrolysis receiving significant focus due to the abundance and accessibility of seawater. However, both direct and indirect seawater electrolysis technologies have a number of practical limitations, including the high energy consumption and maintenance costs associated with seawater desalination systems and the need for strong alkaline conditions. Nevertheless, indirect seawater electrolysis, which amalgamates desalination and water electrolysis processes by employing clean water produced by seawater reverse osmosis (RO) as the feed for water splitting, is currently considered more economical than direct electrolysis. Electrodeionization has also emerged as an alternative to conventional seawater RO due to its high energy efficiency and environmental advantages. In addition, the development of environmentally friendly processes to simultaneously extract high-value compounds from seawater and the brine produced as a by-product from seawater RO can mitigate the high process costs associated with seawater electrolysis and deionization. Recent advancements in seawater electrolysis technologies based on the chlorine evolution reaction (CER) have also been reported, with the generated chlorine harnessed as a resource in other processes. The CER and electrodeionization can be used in a diverse array of other applications, including chlorine-mediated electrochemical redox reactions, the desalination-coupled electrochemical production of acids and bases, resource recovery from seawater and brine, direct ocean CO2 capture, and reverse electrodialysis for green electricity production. In this perspective, we first compare the mechanisms, thermodynamics, and kinetics of the CER with those of the oxygen evolution reaction (OER). Subsequently, we introduce an array of electrodeionization technologies that can be seamlessly integrated with seawater electrolysis systems. We then describe the various applications of seawater electrolysis and electrodeionization technologies, before addressing the remaining challenges and offering insights into the future prospects for the electrochemical utilization of seawater resources.