Z‐Scheme on wires: The two photosystems of the natural photosynthetic Z‐scheme have been connected by immobilizing them within redox hydrogels on individual electrodes. Upon irradiation, this biophotovoltaic device produced photocurrents as a closed and autonomous system. The open‐circuit voltage of the cell corresponds to the potential difference between the two redox hydrogels and indicates the coupling of the two charge separation steps.

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 O2 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.

Photosystem 2 (PS2) that catalyses light driven water splitting in photosynthesis was wired to electrode surfaces via osmium-containing redox polymers based on poly(vinyl)imidazol. The redox polymer hydrogel worked as both immobilization matrix and electron acceptor for the enzyme. Upon illumination, the enzymatic reaction could be switched on and a catalytic current was observed at the electrode. The catalytic current is directly dependent on the intensity of light used for the excitation of PS2. A typical current density of 45 mA cm À2 at a light intensity of 2.65 mW cm À2 could be demonstrated with a significantly improved operational stability.

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Photosystem 1 (PS1) catalyzes the light driven translocation of electrons in the process of oxygenic photosynthesis. Isolated PS1 was immobilised on a gold electrode surface via an Os complex containing redox polymer hydrogel which simultaneously is used as immobilisation matrix and as electron donor for PS1. On addition of methyl viologen as sacrificial electron acceptor, a catalytic photocurrent with densities of up to 29 mA cm À2 at a light intensity of 1.8 mW cm À2 was observed upon illuminationequivalent to an incident photon to carrier efficiency (IPCE) of 3.1%. The strong dependence of the catalytic reaction on the light intensity and the dissolved oxygen concentration indicates that a significant photocurrent from excited PS1 to the electrode can only be realized in the presence of oxygen.