Functions of MnOx in NaCl Aqueous Solution for Artificial Photosynthesis

Abstract

Summary Photoelectrochemical water splitting has been intensively investigated as artificial photosynthesis technology to convert solar energy into chemical energy. The use of seawater and salted water has advantages for minimum environmental burden; however, the oxidation of Cl − ion to hypochlorous acid (HClO), which has toxicity and heavy corrosiveness, should occur at the anode, along with the oxygen evolution. Here, O 2 and HClO production in aqueous solution containing Cl − on photoanodes modified with various metal oxides was investigated. The modification of MnO x resulted in the promotion of the O 2 evolution reaction (OER) specifically without HClO production over a wide range of conditions. The results will contribute not only to the practical application of artificial photosynthesis using salted water but also to the elucidation of substantial function of manganese as the element for OER center in natural photosynthesis.

Enhanced HClO production from chloride by dual cocatalyst loaded WO3 under visible light

“…Some papers have reported that the production of HClO at anodes could be effectively suppressed by coating the anode with MnO x . [40][41][42][43] As shown in Fig. 6, only a small amount of HClO was produced at the MnO x /FTO electrode, and its FE HClO was less than 4%, which demonstrated that isolated MnO x itself is not conducive to the formation of HClO, which is consistent with the reported papers.…”

“…6, only a small amount of HClO was produced at the MnO x /FTO electrode, and its FE HClO was less than 4%, which demonstrated that isolated MnO x itself is not conducive to the formation of HClO, which is consistent with the reported papers. 40–43 Therefore, we believe that the increase in the selectivity toward HClO production over Pt–Mn/WO 3 should mainly come from the synergistic effect between Pt and Mn species despite the presence of MnO x . This result suggests that some of the Pt–Mn cocatalyst is probably used as an oxidation site to improve the selectivity toward HClO production on the surface of WO 3 .…”

A review of sodium chloride-based electrolytes and materials for electrochemical energy technology

“…[208][209][210] Cl À in NaCl solution can be oxidized into Cl 2 and OCl À at the anode under acidic and basic conditions, instead of O 2 evolution by the oxidation of water. 211,212 Although Cl 2 and OCl À produced on a large scale by the electrolysis of brine are the valuable intermediate products in the chlor-alkali industry for disinfection and bleaching, 185,211,213 their toxicity and heavy corrosiveness present a major environmental problem during hydrogen production by water splitting. 184,211 Catalysts as the core components for water splitting in NaCl solution largely determine the hydrogen production efficiency and the selectivity of the chlorine evolution reaction and oxygen evolution reaction.…”

“…211,212 Although Cl 2 and OCl À produced on a large scale by the electrolysis of brine are the valuable intermediate products in the chlor-alkali industry for disinfection and bleaching, 185,211,213 their toxicity and heavy corrosiveness present a major environmental problem during hydrogen production by water splitting. 184,211 Catalysts as the core components for water splitting in NaCl solution largely determine the hydrogen production efficiency and the selectivity of the chlorine evolution reaction and oxygen evolution reaction. Therefore, researchers have devoted a great deal of effort to the development of catalysts having high efficiency and excellent selectivity for hydrogen production by electrocatalysis, photocatalysis and photoelectrocatalysis of NaCl-based solutions.…”

“…Therefore, researchers have devoted a great deal of effort to the development of catalysts having high efficiency and excellent selectivity for hydrogen production by electrocatalysis, photocatalysis and photoelectrocatalysis of NaCl-based solutions. The electrocatalysts reported at present mainly include Pt-based materials, 26,[211][212][213][214][215][216][217][218] Ni-based materials, 23,[218][219][220][221] Mo-based materials, [222][223][224][225] doped carbon materials, 226 and so on. 184 TiO 2based materials 227,228 and Zn-based materials [229][230][231][232] as photocatalysts have broad application prospects.…”