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)(2)Cl 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)PS(-1), which considerably exceeds the rates observed in natural photosynthesis or in other semiartificial systems. Under O-2 supersaturation, photocurrents of 322 +/- 19 mu A cm(-2) were achieved. The photocurrents are only limited by mass transport of the terminal electron acceptor (O-2). This implies that even higher electron-transfer rates may be achieved with PS1-based systems in general.