A noble-metal-free artificial photosynthesis system with TiO2 as electron relay for efficient photocatalytic hydrogen evolution

- A novel FL/Ni1/TiO2 system was developed for H2 generation from fully aqueous solutions.
- Encouraging activity and stability for H2 production was achieved by this system.
- TiO2-mediated quenching of FL∗ and electron transfer benefited photocatalytic H2 generation.

Artificial photosynthesis (AP) systems for hydrogen production are currently attracting immense attention due to their huge potential to convert solar energy into chemical fuels. We developed an efficient AP system containing fluorescein (FL) as photosensitizer, a simple nickel complex (Ni(TEOA)2(Cl)2, Ni1) as catalyst, TiO2 as electron relay, and triethanolamine (TEOA) as sacrificial electron donor for H2 generation from a fully aqueous solution. This FL/Ni1/TiO2 system exhibits considerable photocatalytic activity and stability under visible light, with turnover number (TON, based on Ni1) of 740 after 24 h irradiation, which is 200% that of the FL/Ni1 system. The efficient photocatalytic performance should be attributed to efficient electron transfer from FL to Ni1 as well as TiO2-mediated electron transfer from FL to the nickel metal generated in situ onto TiO2 by photoreduction of Ni1, leading to the increased oxidative quenching of FL∗ by TiO2 and then the inhibited generation of unstable FL− intermediates by reductive quenching. The present study successfully fabricated a typical AP system for visible-light-driven H2 generation and introduced a feasible and facile strategy for designing high-performance AP systems for mediator-engineered electron transfer processes.

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