Earth-abundant iron(iii) species serves as a cocatalyst boosting the multielectron reduction of IO3−/I− redox shuttle in Z-scheme photocatalytic water splitting

Abstract

Z-scheme water splitting has exhibited significant potential for practical water splitting under visible light irradiation. This system comprises two photocatalysts for O₂ and H₂ evolution, along with a redox shuttle for transporting electrons between these photocatalysts. Therefore, the promotion of redox reaction of the shuttle play a crucial role in efficient water splitting. In particular, for multielectron redox reactions (e.g., IO₃⁻/I⁻), a cocatalyst is indispensable, where only noble metals may contribute thus far. Herein, we demonstrate that FeO_x catalyzes the multielectron IO₃⁻ reduction on the Bi₄TaO₈Cl photocatalyst. While bare Bi₄TaO₈Cl does not show O₂ evolution from an aqueous IO₃⁻ solution because of the lack of multielectron reduction ability, FeO_x loading enables O₂ evolution. Based on a series of experimental investigations, such as time-resolved spectroscopy, we elucidated that the O₂ evolution enhancement stems from the promotion of multielectron reduction of IO₃⁻ by FeO_x. The Fe^III/Fe^II redox couple in the loaded FeO_x facilitates both electron carrier capture from Bi₄TaO₈Cl and reduction of the redox mediator. In addition, FeO_x is effective for other photocatalysts and redox mediators. To the best of our knowledge, the developed cocatalysts is the first earth-abundant cocatalyst for multielectron redox mediators.