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.