High Selectivity Electrocatalysts for Oxygen Evolution Reaction and Anti-Chlorine Corrosion Strategies in Seawater Splitting

Abstract

Seawater is one of the most abundant and clean hydrogen atom resources on our planet, so hydrogen production from seawater splitting has notable advantages. Direct electrolysis of seawater would not be in competition with growing demands for pure water. Using green electricity generated from renewable sources (e.g., solar, tidal, and wind energies), the direct electrolytic splitting of seawater into hydrogen and oxygen is a potentially attractive technology under the framework of carbon-neutral energy production. High selectivity and efficiency, as well as stable electrocatalysts, are prerequisites to facilitate the practical applications of seawater splitting. Even though the oxygen evolution reaction (OER) is thermodynamically favorable, the most desirable reaction process, the four-electron reaction, exhibits a high energy barrier. Furthermore, due to the presence of a high concentration of chloride ions (Cl−) in seawater, chlorine evolution reactions involving two electrons are more competitive. Therefore, intensive research efforts have been devoted to optimizing the design and construction of highly efficient and anticorrosive OER electrocatalysts. Based on this, in this review, we summarize the progress of recent research in advanced electrocatalysts for seawater splitting, with an emphasis on their remarkable OER selectivity and distinguished anti-chlorine corrosion performance, including the recent progress in seawater OER electrocatalysts with their corresponding optimized strategies. The future perspectives for the development of seawater-splitting electrocatalysts are also demonstrated.

Efficient Cocatalyst-Free Piezo-Photocatalytic Hydrogen Evolution of Defective BaTiO3–x Nanoparticles from Seawater

“…The difference between simulated and natural seawater is attributed to the greater concentrations of K + , Mg 2+ , Ca 2+ , and SO 4 2− . 5 Ji et al 53 showed that Mg 2+ can reduce significantly the H 2 evolution. These findings were supported by those of Li et al, 53 who showed that the chelation of Mg 2+ blocks the separation of photogenerated electron−hole excitons and induce charge redistribution, thereby negatively impacting on the photocatalytic performance.…”

“…53,54 Another factor is the blockage of surface active sites by these ions as well as by suspended and dissolved species. 5 Solids suspended in seawater decrease light absorption by scattering and dissolved species may alter the refractive index and so increase reflection. These effects also can provide the energy to trigger biochemical reactions that can reduce the H 2 production as well.…”

“…In light of Na adsorption and retention on the nanoparticles, these data suggest that NaCl is the main factor behind these differences, where Na + would cause electron ( e – ) scavenging and Cl – would cause hole ( h + ) scavenging. The difference between simulated and natural seawater is attributed to the greater concentrations of K + , Mg 2+ , Ca 2+ , and SO 4 2– . Ji et al showed that Mg 2+ can reduce significantly the H 2 evolution.…”

“…Seawater is the most abundant aqueous feedstock on earth but there are three principal challenges that will determine the feasibility of direct seawater splitting. First, the similarity of the electrochemical potentials of the OER at 1.23 eV and the chlorine evolution reaction (CER) at 1.36 eV raises the possibility of the production of chlorine-containing products (e.g., chlorine gas, hypochlorous acid, or hypochlorite) . Second, the presence of such scavengers in seawater, e.g., the hole scavenger Cl – , is disadvantageous because they can compete with the HER and OER for catalytically generated electrons and holes, respectively.…”

“…First, the similarity of the electrochemical potentials of the OER at 1.23 eV and the chlorine evolution reaction (CER) at 1.36 eV raises the possibility of the production of chlorine-containing products (e.g., chlorine gas, hypochlorous acid, or hypochlorite). 5 Second, the presence of such scavengers in seawater, e.g., the hole scavenger Cl − , is disadvantageous because they can compete with the HER and OER for catalytically generated electrons and holes, respectively. The competition between HER and OER is affected by the electron reactions.…”