Recent Advances on Hydrogen Evolution and Oxygen Evolution Catalysts for Direct Seawater Splitting

Abstract

Producing hydrogen via water electrolysis could be a favorable technique for energy conversion, but the freshwater shortage would inevitably limit the industrial application of the electrolyzers. Being an inexhaustible resource of water on our planet, seawater can be a promising alternative electrolyte for industrial hydrogen production. However, many challenges are hindering the actual application of seawater splitting, especially the competing reactions relating to chlorine at the anode that could severely corrode the catalysts. The execution of direct seawater electrolysis needs efficient and robust electrocatalysts that can prevent the interference of competing reactions and resist different impurities. In recent years, researchers have made great advances in developing high-efficiency electrocatalysts with improved activity and stability. This review will provide the macroscopic understanding of direct seawater splitting, the strategies for rational electrocatalyst design, and the development prospects of hydrogen production via seawater splitting. The nonprecious metal-based electrocatalysts for stable seawater splitting and their catalytic mechanisms are emphasized to offer guidance for designing the efficient and robust electrocatalyst, so as to promote the production of green hydrogen via seawater splitting.

Materials Design and System Innovation for Direct and Indirect Seawater Electrolysis

“…However, further research revealed that the quality of RO-treated seawater (with trace residual ions, especially Cl − ) is not high enough to be directly used by PEM electrolyzers, which may poison the catalysts/ electrodes or accelerate membranes degradation. 85 It necessitates further purification by more advanced technologies, such as multistage flash distillation, multi effect distillation or electrodeionization. 86 The maintenance, energy consumption and land occupation of additional purification devices will lead to a significant increase in costs.…”

“…The seawater desalination system includes the RO unit and necessary physical/chemical pretreatment steps depending on raw feedwater quality. However, further research revealed that the quality of RO-treated seawater (with trace residual ions, especially Cl – ) is not high enough to be directly used by PEM electrolyzers, which may poison the catalysts/electrodes or accelerate membranes degradation . It necessitates further purification by more advanced technologies, such as multistage flash distillation, multi effect distillation or electrodeionization .…”

Recent advances in direct seawater splitting for producing hydrogen

“…32 Similarly, some oxygen-containing anions (such as PO 4 3− , SO 4 2− , and NO 3 − ) have also been reported to reduce the selectivity of anodic chlorine evolution. 13,32–35 For example, Dai et al synthesized a multilayer anode catalyst (NiFe/NiS x –Ni) with nickel–iron hydroxide uniformly coated on nickel sulfide on foam nickel (Fig. 4(d)).…”

Research prospects of graphene-based catalyst for seawater electrolysis

“…These impurities are easily attached to the catalyst surface, thus hindering the direct contact between the electrolyte and the catalyst active sites, thus severely reducing the catalyst life in seawater electrolysis. Most reported HER catalysts to decay by more than 50% within 24 h in seawater electrolysis [34]. These issues require researchers to develop 'new corrosion-resistant electrolysis seawater catalysts'.…”