https://neovisionconsulting.blogspot.com/2023/01/blog-post_31.html
AIST: Highly selective production of hydrogen and oxygen from seawater by artificial photosynthesis
National Institute of Advanced Industrial Science and Technology (AIST) , Artificial photosynthesis technology
October 26, 2020
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The National Institute of Advanced Industrial Science and Technology (AIST) has recently developed an artificial photosynthesis technology that selectively produces hydrogen and oxygen at low electrolytic voltage from aqueous solutions containing chloride ions, such as salt water and seawater, by irradiating an oxide semiconductor photoelectrode that responds to visible light with sunlight.
They found that only a small amount of manganese oxide loaded on the photoelectrode surface suppresses hypochlorous acid (HClO) formation. In addition to the realization of a hydrogen production system using artificial photosynthesis technology with photoelectrodes, this finding suggests a key to solving the reason why manganese is the center of oxygen generation in natural photosynthetic systems, and is expected to contribute to both practical applications and basic research.
The technology to produce hydrogen and oxygen by water splitting with photoelectrodes and photocatalysts using sunlight is low-cost and clean, and is being actively researched as a fundamental technology for the realization of a hydrogen society. The use of seawater is low-cost, but it produces HClO from chloride ions in seawater along with oxygen. Although the sterilization and disinfection functions are useful, they accelerate corrosion and degradation of the system, so there is a need to develop photoelectrodes that selectively produce only oxygen.
The oxide semiconductor photoelectrode BiVO4/WO3/FTO developed by AIST uses sunlight to efficiently decompose water at low voltage to generate hydrogen and oxygen. A precursor solution containing various metal ions was applied and sintered on the surface of this photoelectrode, resulting in metal oxide modification.
The ability of these photoelectrodes to produce oxygen and HClO was evaluated in an electrochemical reaction system using a sodium chloride (NaCl)-containing reaction solution in a two-chamber reaction vessel with an ion exchange membrane. The unmodified photoelectrode produced oxygen and HClO simultaneously, but only the manganese-modified photoelectrode produced almost no HClO and showed an oxygen selectivity of over 90%.
The effects of NaCl concentration, pH, differences in crystal structures of manganese precursors and manganese oxides, and complexation with different elements were small, and oxygen was selectively generated under a wide range of conditions. It was reproduced even in artificial seawater containing a wide variety of coexisting ions. This specificity of manganese was suggested to be due to its unique catalytic activity, in which the overvoltage of HClO generation was significantly higher relative to oxygen generation.
The oxygen-evolving center of natural photosynthesis is composed of manganese oxide aggregates, and we have proposed a new hypothesis that the specificity of manganese to inhibit HClO formation, which is harmful to organisms, under a wide range of conditions is involved in the evolution of the oxygen-evolving center. In the future, they intend to conduct research and development aimed at the practical application of hydrogen production by sunlight, such as improving the long-term stability of the photoelectrode developed this time, and also to prove the evolutionary hypothesis of natural photosynthesis.
Translated with www.DeepL.com/Translator (free version)
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