Photosensitization of Ir-Dye on TiO₂ for Enhanced Hydrogen Evolution: Presence of Ferrocene Matters

Dye-sensitized photochemical hydrogen evolution is potentially promising and ecofriendly but often suffers from low stability and photocatalytic activities. The Ir(III) complex plays an important role in photoinduced energy and electron transfer processes, along with excellent luminescence properties, such as high emission intensities and long lifetimes. In this work, a heterobimetallic Fe∧Ir photosensitizer has been rationally designed and synthesized for solar hydrogen evolution application. Harnessing visible light with a significantly high lifetime of 592 ns of bimetallic boosts hydrogen evolution performance compared to a monometallic system, i.e., without a ferrocene auxiliary (390 ns). The longer lifetime of Fe∧Ir-dye is attributed to the extension of π-conjugation achieved by the ferrocene moiety into the ancillary ligand. The investigated materials exhibited the highest rate of ∼8.04 mmol g–1 h–1 (AQY = 19.68%, TON = 14894) under visible light, and at neutral pH. Fe∧Ir-dye demonstrates quasi-reversible redox processes for IrIII/IV alongside a reversible reduction of bpy0/bpy–1. The induction of redox-active ferrocene in Fe∧Ir-dye altered the overall electronic properties of the catalyst. The light-harvesting ability, theoretical molecular orbital levels, and redox potential behavior of the dye-sensitized photocatalysts are systematically investigated, complementing the superior activity of the designed material.