Comprehensive understanding of efficient Electrocatalysts for seawater splitting: Challenges, advances and prospects

With the large-scale adoption of hydrogen production technology via water electrolysis, the demand for freshwater resources will increase markedly, particularly in those coastal regions where freshwater is in shortage. Seawater constitutes 97.5 % of the total global water resources. Consequently, obtaining hydrogen by electrolyzing seawater can effectively alleviate the bottleneck issue resulting from freshwater scarcity. Nevertheless, seawater contains multiple ions that compete with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) during the water electrolysis process, and the by-products generated might poison the catalyst, cause environmental pollution, and clog the electrolytic cell. Therefore, the challenges encountered when applying the seawater electrolysis catalysts developed in the laboratory to practical production are far greater than those in pure water electrolysis. In recent years, researchers have explored various metal-based catalysts, including abundant transition metal oxides, noble metal oxides, and their mixtures, some of which have demonstrated outstanding activity and selectivity in seawater electrolysis. This paper reviews the mechanisms of OER and HER under alkaline and acidic conditions, as well as the challenges posed by chloride ions and metal cations in seawater to electrocatalysts, discusses the design concepts and research progress of electrocatalysts aimed at enhancing activity, stability, and corrosion resistance, summarizes and expounds the synthesis strategies, catalytic performance, action mechanisms, and application prospects of different types of seawater electrocatalysts, and looks forward to future research directions such as improving the activity of seawater OER and anti-chloride corrosion through catalyst reconstruction. • Unified dual-challenge analysis: Links fundamental seawater electrochemistry with catalyst degradation mechanisms, bridging theory and practice. • Element classification overview: Summarizes catalyst design principles & strategies by element, highlighting current deficiencies. • Critical scalability barriers: Identifies membrane fouling, long-term fluctuating salinity stability, and >1000 mA/cm 2 operation hurdles. • Applied challenges ahead: Outlines “Material-Device-System” optimization via electrolyte engineering, in-situ regeneration, and renewable grid integration. • This review uniquely integrates the fundamental principles of electrocatalytic seawater splitting with the actual degradation mechanisms of catalysts, systematically analyzing the dual challenge mechanisms and providing a hierarchical classification of the latest breakthroughs in catalyst engineering. • It also offers a critical assessment of scalability barriers and outlines an optimization pathway for 'materials-devices-systems' tailored to practical applications.