Efficient Hydrogen Production by a Photoredox Cascade Catalyst Comprising Dual Photosensitizers and a Transparent Electron Mediator

Abstract

One-directional electron transport between a photocatalyst and redox mediator is crucial for achieving highly active Z-scheme water-splitting photocatalysis. Herein, a photoredox cascade catalyst that artificially mimics the electron transport chain in natural photosynthesis was synthesized from a Pt-TiO₂ nanoparticle catalyst, two photosensitizers (RuCP⁶ and RuP⁶), and a visible-light-transparent electron mediator (HCRu). During photocatalytic hydrogen evolution in the presence of a redox-reversible electron donor, [Co(bpy)₃]²⁺ (bpy = 2,2'-bipyridine), the HCRu-Zr-RuCP⁶-Zr-RuP⁶@Pt-TiO₂ (PRCC-1) photocatalyst exhibited the highest reported initial (1 h) apparent quantum yield (iAQY = 2.23%) of dye-sensitized TiO₂ photocatalysts to date. Furthermore, PRCC-1 successfully produced hydrogen when using hydroquinone monosulfonate (H₂QS^-) as the hydrogen source.

Figure 1

Surface structure and energy diagram of PRCC-n (n = 1, 2; HCM = HCRu, HCFe) for photocatalytic H₂ production. The BQSK/H₂QSK redox potential was estimated by cyclic voltammetry (Figure S6), and the other redox potentials were inferred from the literature.^,,

Figure 2

Photocatalytic H₂ production driven by PRCC-1 (blue solid circles), PRCC-2 (black solid circles), and DDSP (red open squares) in the presence of (a) 16.4 mM [Co(bpy)₃]SO₄ and (b) 0.5 M H₂QSK as the electron donor in HCl aqueous solution (initial pH = 2.0) under blue light irradiation (λ = 460 ± 15 nm; 70 mW). The Ru(II) dye concentration was 100 μM for all reactions.