Harvesting electrical current from intact plant leaves

Efforts to replace fossil fuels with renewable energy technologies, especially solar energy conversion, continue to improve the potential to produce useful amounts of energy without significant pollution. Utilization of photosynthetic organisms in bio-photo electrochemical cells (BPECs) are a potentially important source of clean energy. Here, we show that it is possible to harvest photocurrent directly from unprocessed plant tissues in specialized BPECs. The source of electrons are shown to originate from the Photosystem II water-oxidation reaction that results in oxygen evolution. In addition to terrestrial and crop plants, we further demonstrate the ability of the desert plant Corpuscularia lehmannii to produce bias-free photocurrent without the addition of an external electrolyte. Finally, we show the use of pond-grown water lilies to generate photocurrent. Different leaves produce photocurrent densities in the range of ∼ 1 – 10 mA / cm2 which is significantly higher than microorganism-based BPECs. The relatively high photocurrent and the simplicity of the plants BPEC may pave the way toward the establishment of first applicative photosynthetic based energy technologies.Broader ContextIt is no secret human society is experiencing an energy and environmental crisis due to our reliance on fossil fuels. In order to promote alternative, cleaner, and more sustainable approaches to energy production, we wish to explore the possibility of using nature’s method of solar energy conversion in the simplest, least polluting, most sustainable fashion possible. Photosynthesis provides a remarkable example of molecular system for solar energy conversion to storable fuels. Many studies have strived to merge natural photosynthesis (as isolated complexes, isolated membranes, or intact microorganisms) with a variety of electrochemical harvesting technologies. In this paper we show that we can directly couple the power of water oxidation by Photosystem II in intact plants to bio-electrochemical cells without the need to perform expensive, complicated, and polluting isolation. We show that current harvesting (up to current densities of 10 mA / cm2) can be performed using plants of different types: plants of agricultural importance, succulents with internal water-based reservoirs and aquatic plants, used in situ in their growth ponds. We also show that with minimal external bias, hydrogen can be obtained, to be used as a clean fuel. We believe that these results can lead to the development of localized clean energy technologies, where the benefits of plant growth for any purpose can be enhanced by obtaining significant amounts of clean energy.