Dark Photocatalysis via Long-Term Storage of Photoinduced Electrons in {Black-TiO _<i>x</i> /Ag ⁰ } Heterojunctions

Dark photocatalysts allow storage of photogenerated electrons and their post-irradiation use under no-light conditions. This requires the development of materials able to perform photogeneration of electrons, long-term in situ charge storage, and controlled transfer to acceptors on demand. Herein, we present {Black-TiOx/Ag0} nanohybrids consisting of {Black-TiOx} decorated with plasmonic Ag0 nanoparticles produced by flame spray pyrolysis (FSP). A library of {Black-TiOx/Ag0} nanocomposites was engineered, with precise control over Ag0 loading and {Black-TiOx} particle size. Under dark photocatalysis conditions, pre-irradiated {Black-TiOx/Ag0} exhibits significant capacity to store and transfer electrons to Cr6+ or Cu2+ ions under dark conditions. Specifically, pre-irradiated {Black-TiOx/Ag0} provides 0.6 × and 2.3 × 1021 electrons g−1 of {Black-TiOx/Ag0} to Cr6+ ions and Cu2+ ions, respectively, for at least 120 min. Operando electron paramagnetic resonance (EPR) spectroscopy reveals that Magnéli -TiOx surface sites on {Black-TiOx/Ag0} act as efficient trap/store units of the photoexcited electrons. The interfacial Magnéli islands introduce sub-gap energy states in TiO2, drastically improving both electron storage and visible-light activity compared to conventional TiO2/Ag0. Photoluminescence and photoelectrochemical analyses show that {Black-TiOx/Ag0} exhibits high electron mobility and low hole/electron recombination rates. This analysis reveals that the interfacial Magnéli islands in contact with Ag0 act [i] as efficient electron storage pools of surface electrons under sunlight and [ii] as long-lived electron donors in the dark. This work provides a first proof-of-concept for {Black-TiOx/Ag0} nanocomposites as photochargeable battery-like materials, enabling decoupled dark redox chemistry, while highlighting FSP as a versatile and scalable route for their synthesis.