Photocatalytic water splitting employing a [Fe(CN)6]3−/4− redox mediator under visible light

Abstract

Photocatalytic Z-scheme water splitting is attracting increasing attention as a promising technology for converting solar energy to hydrogen energy. We studied Z-scheme water splitting using a [Fe(CN)₆]^3−/4− redox mediator that can function at neutral pH. Surface-modified WO₃ (denoted as Fe–H–Cs–WO₃) showed an excellent activity for the water oxidation reaction using [Fe(CN)₆]³⁻. Oxygen was produced when all the [Fe(CN)₆]³⁻ ions were reduced to [Fe(CN)₆]⁴⁻ ions. The surface modification of WO₃ effectively suppressed the undesirable reaction between the photogenerated holes and [Fe(CN)₆]⁴⁻ ions. Furthermore, water splitting proceeded steadily via the Z-scheme system combining the powder photocatalysts, Fe–H–Cs–WO₃ and Ru/SrTiO₃:Rh. The turnover number for the amount of reacted electrons/holes to the molar quantity of [Fe(CN)₆]^3−/4− ions reached 32 for a reaction time of 86 h.