Photoelectrochemical Wiring of Paulschulzia pseudovolvox (Algae) to Osmium Polymer Modified Electrodes for Harnessing Solar Energy

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%. The photo-electrogenic activity of a green alga, Paulschulzia pseudovolvox, is shown, and the electron transfer from photolysis of water via the green alga cells to the electrode is revealed to be either directly or mediated by an osmium redox polymer. When benzoquinone is added to the electrolyte and the cells are protected from reactive oxygen species by the addition of superoxide dismutase, the maximum photocurrent recorded was 11.50 μA cm^-2. In the presence of an inhibitor specific for photosystem II, diuron, the photocurrent decreases by 50%.