Surface Modification with Metal Hexacyanoferrates for Expanding the Choice of H2‐Evolving Photocatalysts for Both Fe3+/Fe2+ Redox‐Mediated and Interparticle Z‐Scheme Water‐Splitting Systems

Abstract

The construction of Z‐scheme water splitting systems is an effective approach toward harvesting a wide portion of the solar light spectrum; however, the success has often depended on the property of photocatalyst surfaces. This drawback is typified by the limited choice of efficient H2 evolution photocatalysts (HEPs) (e.g., Rh‐doped SrTiO3) for Z‐scheme water splitting using Fe3+/Fe2+ redox couple. The majority of visible light‐responsive materials shows low activity for H2 production with Fe2+ electron donors despite having suitable band levels, probably due to the absence of an effective surface site for oxidizing Fe2+. The choice of HEPs for interparticle Z‐scheme systems has also been limited. Herein, an effective strategy for overcoming these limitations is reported: activation of originally inactive materials via surface modification with metal hexacyanoferrate nanoparticles. Photocatalytic H2 evolution over TaON in aqueous Fe2+ solution is drastically enhanced by comodification with indium hexacyanoferrate (InHCF) and Rh–Cr mixed oxide. InHCF promotes Fe2+ oxidation to Fe3+ utilizing the holes photogenerated in TaON via FeIII/FeII redox cycles, enabling Z‐scheme water splitting with the Fe3+/Fe2+ redox mediator coupled with an O2 evolution photocatalyst under visible light. It is also disclosed that InHCF nanoparticles function as effective solid electron mediators for achieving interparticle Z‐scheme water splitting.