Engineered electron-transfer chain in photosystem 1 based photocathodes outperforms electron-transfer rates in natural photosynthesis

Photosystem 1 (PS1) triggers the most energetic light-induced charge-separation step in nature and the in vivo electron-transfer rates approach 50 e^- s^-1 PS1^-1. Photoelectrochemical devices based on this building block have to date underperformed with respect to their semiconductor counterparts or to natural photosynthesis in terms of electron-transfer rates. We present a rational design of a redox hydrogel film to contact PS1 to an electrode for photocurrent generation. We exploit the pH-dependent properties of a poly(vinyl)imidazole Os(bispyridine)₂Cl polymer to tune the redox hydrogel film for maximum electron-transfer rates under optimal conditions for PS1 activity. The PS1-containing redox hydrogel film displays electron-transfer rates of up to 335±14 e^- s^-1 PS1^-1, which considerably exceeds the rates observed in natural photosynthesis or in other semiartificial systems. Under O ₂ supersaturation, photocurrents of 322±19 μA cm ^-2 were achieved. The photocurrents are only limited by mass transport of the terminal electron acceptor (O₂). This implies that even higher electron-transfer rates may be achieved with PS1-based systems in general.