Photosynthetic microbial fuel cells (PMFCs) are an emerging technology for renewable solar energy conversion. Major efforts have been made to explore the electrogenic activity of cyanobacteria, mostly using practically unsustainable reagents. Here we report on photocurrent generation (≈8.64 μA cm(-2)) from cyanobacteria immobilized on electrodes modified with an efficient electron mediator, an Os(2+/3+) redox polymer. Upon addition of ferricyanide to the electrolyte, cyanobacteria generate the maximum current density of ≈48.2 μA cm(-2).

Thylakoid membranes (TMs) are uniquely suited for photosynthesis owing to their distinctive structure and composition. Substantial efforts have been directed towards use of isolated photosynthetic reaction centers (PRCs) for solar energy harvesting, however, few studies investigate the communication between whole TMs and electrode surfaces, due to their complex structure. Here we report on a promising approach to generate photosynthesis-derived bioelectricity upon illumination of TMs wired with an osmium-redox-polymer modified graphite electrode, and generate a photocurrent density of 42.4 μA cm(-2).

Studies on biological photovoltaics based on intact organisms are challenging and in most cases include diffusing mediators to facilitate electrochemical communication with electrodes. However, using such mediators is impractical. Instead, surface confined Os‐polymers have been successfully used in electrochemical studies including oxidoreductases and bacterial cells but not with algae. Photoelectrogenic activity of a green alga, Paulschulzia pseudovolvox, immobilized on graphite or Os‐polymer modified graphite is demonstrated. Direct electron transfer is revealed, when no mediator is added, between algae and electrodes with electrons emerging from photolysis of water via the cells to the electrode exhibiting a photocurrent density of 0.02 μA cm−2. Os‐polymers with different redox potentials and structures are used to optimize the energy gap between the photosynthetic complexes of the cells and the Os‐polymers and those of greater solubility, better accessibility with membranes, and relatively higher potentials yielded a photocurrent density of 0.44 μA cm−2. When benzoquinone is included to the electrolyte, the photocurrent density reaches 6.97 μA cm−2. The photocurrent density is improved to 11.50 μA cm−2, when the cells are protected from reactive oxygen species when either superoxide dismutase or catalase is added. When adding an inhibitor specific for photosystem II, diuron, the photocurrent is decreased by 50%.

Recently, interest in photosynthetic energy conversion has substantially increased. Chloroplasts, the photosynthetic organelle inside higher plants and algae, are the ultimate source of carbon-based fuels. However, they have been less studied in a photobioelectrochemical cell, because their electrochemical communication at an electrode surface is challenging due to their complex membrane system. Although redox polymers are widely used for mediating bioelectrocatalysis, they have never been explored for wiring chloroplasts to electrodes. Herein, a naphthoquinone-functionalized linear poly­(ethylenimine) (NQ-LPEI) redox polymer is used as an electron transfer (ET) mediator as well as the immobilization matrix for chloroplasts. They are immobilized on Toray carbon paper electrodes (TPs), and the photoexcited ET from water oxidation is evaluated, showing that intact chloroplasts can undergo direct electron transfer (DET) and mediated electron transfer (MET). Photocurrent generation by DET of chloroplasts results in an oxidative current of 1.5 ± 0.2 μA cm–2. On NQ-LPEI modified electrodes, the oxidative photocurrent increased to 4.7 ± 0.7 μA cm–2 and further improved to 29 ± 6 μA cm–2 in the presence of an additional diffusive mediator, 2,6-dichlorobenzoquinone (DCBQ). The oxidative current produced in the presence of light confirms the ability to oxidize water (H2O) at a chloroplast-modified electrode surface.

Photosynthesis is a sustainable process for the conversion of light energy into chemical energy. Thylakoids in energy‐transducing photosynthetic membranes are unique in biological membranes because of their distinguished structure and composition. The quantum trapping efficiency of thylakoid membranes is appealing in photobioelectrochemical research. In this study, thylakoid membranes extracted from spinach are shown to communicate with a gold‐nanoparticle‐modified solid gold electrode (AuNP–Au) through a series of quinone derivatives. Among these, para‐benzoquinone (PBQ) is found to be the best soluble electron‐transfer mediator, generating the highest photocurrent of approximately 130 μA cm−2 from water oxidation under illumination. In addition, the photocurrent density is investigated as a function of applied potential, the effect of light intensity, quinone concentration, and amount of thylakoid membrane. Finally, the source of photocurrent is confirmed by using 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (known by its trade name, Diuron), an inhibitor of photosystem II, which decreases the total photocurrent by 50 %.