2022 年 130 巻 7 号 p. 395-402
Photoelectrochemical (PEC) production of H2 from saltwater over a semiconductor photoelectrode under solar-light irradiation is one of the effective technologies for developing a cost-effective sustainable energy conversion process. However, because saltwater such as seawater contains Cl−, O2 and HClO are produced competitively during oxidation reactions by photogenerated holes from electrolytes containing Cl− during the photo-electrolysis reaction. HClO is a high value-added chemical used for bleaching, etc., however, it is also an undesirable chemical that accelerates corrosion deterioration of large-scale water splitting systems. Therefore, it is necessary to control selectivity of oxidative O2/HClO production in electrolytes containing Cl− over photoelectrodes. In this review, we summarized our recent innovations in selective O2 or HClO production over the visible-light driven BiVO4/WO3 photoanodes by simple modification of metal oxides. Modifications of metal oxides such as MnOx or CoOx via spin-coating onto a photoelectrode could control the selectivity on the O2/HClO production from an aqueous solution containing Cl− effectively. In addition, controlling loading conditions such as the loading amount of metal oxides, and calcination temperatures after coating a metal precursor solution enabled us to prepare photoelectrodes that produce O2 or HClO with selectivity of almost 100 % using MnOx or CoOx, respectively, along with maintaining their PEC performance under solar-light irradiation.
