Earth-abundant iron( iii ) species serves as a cocatalyst boosting the multielectron reduction of IO 3 − /I − redox shuttle in Z-scheme photocatalytic water splitting

Z-scheme water splitting has exhibited significant potential for practical water splitting under visible light irradiation. This system comprises two photocatalysts for O 2 and H 2 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., IO 3 − /I − ), a cocatalyst is indispensable, where only noble metals may contribute thus far. Herein, we demonstrate that FeO x catalyzes the multielectron IO 3 − reduction on the Bi 4 TaO 8 Cl photocatalyst. While bare Bi 4 TaO 8 Cl does not show O 2 evolution from an aqueous IO 3 − solution because of the lack of multielectron reduction ability, FeO x loading enables O 2 evolution. Based on a series of experimental investigations, such as time-resolved spectroscopy, we elucidated that the O 2 evolution enhancement stems from the promotion of multielectron reduction of IO 3 − by FeO x . The Fe III /Fe II redox couple in the loaded FeO x facilitates both electron carrier capture from Bi 4 TaO 8 Cl 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.