Creation of anaerobic microenvironments by photosystem I in porous glass nanopores enables photoinduced H2 evolution under aerobic conditions

Abstract

Under aerobic conditions, artificial photosynthesis devices must maintain a steady electron flow toward H₂ evolution. Dissolved O₂ competes for photogenerated electrons, diverting them into oxygen reduction pathways instead of hydrogen production. In this study, we immobilized photosystem I (PSI) in a porous glass plate (PGP) with 50 nm diameter through-thickness nanopores and analyzed electron transfer using transient absorption kinetics. A kinetic model resolves three processes following charge separation: charge recombination with rate constant k₁, electron loss from the terminal iron–sulfur cluster F_B⁻ in the reduced state to external oxidants, including O₂, with rate constant k₂, and re-reduction of the oxidized reaction center chlorophyll P700 by an external electron donor with rate constant k₃. Remarkably, illumination of a device in which PSI is immobilized in the PGP caused the rate constant k₂ to decrease from 6.5 s⁻¹ at 0 min to 1.2–1.3 s⁻¹ after 7–10 min. This shows that photochemical O₂ consumption by PSI decreases the intrapore O₂ concentration, suppressing electron transfer from F_B⁻ to oxidants. Combined with diffusion-limited O₂ delivery, a local low-O₂ microenvironment is formed within the nanopores over time. Extending this concept to a PSI–Pt nanoparticle assembly (PSI–PtNP), we observed sustained light-driven H₂ evolution under aerobic conditions in PGP-immobilized PSI–PtNP, whereas the bulk solution showed much lower activity under aerobic conditions. The system achieved a turnover number of 400 ± 100 mol H₂ per mol PSI and an O₂ tolerance of 44 ± 15%. These findings establish a framework for reaction field engineering in nanopores and guide the design of oxygen-tolerant systems.