A rational approach for a photosystem II-based electrode assembly is described, integrating redox polymers with high surface area hierarchically structured electrodes.

An oriented photosystem I monolayer with minimised short-circuiting provides anisotropic electron flow, further coupling to a hydrogenase for realising light-induced H2 evolution.

The improvement of Z-scheme inspired biophotovoltaics is achieved by fine tuning the properties of redox hydrogels applied as immobilization and electron conducting matrices for the photosystem-protein complexes. The formal potentials of the redox hydrogels are adjusted to the respective redox sites in the photosystems for optimized electron transfer without substantial voltage loss. The anode is based on photosystem 2 (PS2) integrated in a phenothiazine modified redox hydrogel with a formal potential of -1 mV vs. SHE, which is 59 mV more positive than the QB acceptor site in PS2. The cathode is based on photosystem 1 (PS1) contacted via an Os-complex based redox hydrogel with a formal potential of 395 mV vs. SHE, i.e. 28 mV more negative than the primary P700 electron acceptor of PS1. The potential difference between the two redox hydrogels is 396 mV. An open circuit voltage (VOC) of 372.5 ± 2.1 mV could be achieved for the biophotovoltaic cell. The maximum power output is 1.91 ± 0.56 μW cm(-2) and the conversion efficiency (η) is 4.5 × 10(-5), representing a 125-fold improvement in comparison to the previously proposed device exploiting the photosynthetic Z-scheme for electrical energy production.

We report on a biophotocathode based on photosystem 1 (PS1)-Pt nanoparticle complexes integrated in a redox hydrogel for photoelectrocatalytic H2 evolution at low overpotential. A poly(vinyl)imidazole Os(bispyridine)2Cl polymer serves as conducting matrix to shuttle the electrons from the electrode to the PS1-Pt complexes embedded within the hydrogel. Light induced charge separation at the PS1-Pt complexes results in the generation of photocurrents (4.8 ± 0.4 μA cm(-2)) when the biophotocathodes are exposed to anaerobic buffer solutions. Under these conditions, the protons are the sole possible electron acceptors, suggesting that the photocurrent generation is associated with H2 evolution. Direct evidence for the latter process is provided by monitoring the H2 production with a Pt microelectrode in scanning electrochemical microscopy configuration over the redox hydrogel film containing the PS1-Pt complexes under illumination.

Interfacing photosynthetic proteins specifically photosystem 1 (PS1) with electrodes enables light-induced charge separation processes for powering semiartificial photobiodevices with, however, limited long-term stability. Here, we present the in-depth evaluation of a PS1/Os-complex-modified redox polymer-based biocathode by means of scanning photoelectrochemical microscopy. Focalized local illumination of the bioelectrode and concomitant collection of H2O2 at the closely positioned microelectrode provide evidence for the formation of partially reduced oxygen species under light conditions. Long-term evaluation of the photocathode at different O2 concentrations as well as after incorporating catalase and superoxide dismutase reveals the particularly challenging issue of avoiding the generation of reactive species. Moreover, the evaluation of films prepared with inactivated PS1 and free chlorophyll points out additional possible pathways for the generation of oxygen radicals. To avoid degradation of PS1 during illumination and hence to enhance the long-term stability, the operation of biophotocathodes under anaerobic conditions is indispensable.

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Integration of a 10 MDa light-harvesting photosystem II super-complex into macro-puorous indium tin oxide biophotoanodes for improved energy conversion.

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