Prussian Blue Analogue Materials for Seawater Splitting: A Review.

Seawater electrolysis is emerging as a key alternative strategy for sustainable hydrogen production in water-scarce regions such as the Atacama Desert; however, the high concentration of chloride ions poses significant challenges related to material stability, selectivity, and corrosion resistance. In this context, Prussian Blue Analogues (PBAs) have recently gained attention as multifunctional materials capable of operating in highly saline environments such as seawater. This review provides a critical analysis of PBAs as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in seawater and brine systems, with a particular emphasis on nickel hexacyanoferrate (NiHCF), cobalt hexacyanoferrate (CoHCF), and copper hexacyanoferrate (CuHCF). In addition, a comparative analysis across different electrochemical applications is presented, highlighting the limited number of studies conducted under real seawater conditions. Furthermore, the limitations of current electrochemical evaluation protocols are discussed, and a framework for realistic benchmarking under saline conditions is proposed. Finally, emerging opportunities in hybrid materials and high-entropy PBAs are addressed, positioning PBAs as a promising platform for next-generation electrochemical technologies for sustainable solar hydrogen production from seawater or highly chloride-concentrated brines.