Controlling the selectivity of solar O2/HClO production from seawater by simple surface modification of visible-light responsible photoelectrodes

Abstract

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 Cl1, O2 and HClO are produced competitively during oxidation reactions by photogenerated holes from electrolytes containing Cl1 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 Cl1 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 Cl1 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.