Bio-mimic energy storage system with solar light conversion to hydrogen by combination of photovoltaic devices and electrochemical cells inspired by the antenna-associated photosystem II.

Global warming caused by anthropogenic activity is one of the serious problems today. In order to suppress the global warming, the shift from fossil fuel-based energy source to the nature-oriented sustainable energy is encouraged. In this concept paper, possible biomimetic engineering approach inspired by the efficient and sustainable natural energy utilization in living plants is demonstrated. The focal features in plants include (1) the light-harvesting and energy condensing apparatus, (2) water splitting O2 evolving apparatus, (3) storage of energy-related chemicals, and (4) reversal conversion of storage into the "energy in use" by meeting the demands. Demonstration of solar-driven chemical energy conversion was performed using a system consisted of (i) photovoltaic power-generating device, (ii) an electrochemical unit converting electric power into chemical energy, (iii) storage of H2, and (iv) polymer electrolyte cells converting H2 back to electricity by meeting the demands on site. The present concept paper presenting a technical perspective based on the plant-inspired knowledge (conceptual similarity between natural photosynthesis and solar-to-H2 conversion) is a fruit of interdisciplinary collaboration between the team of chemical energy conversion renown for the world highest record of solar-to-hydrogen conversion efficiency (24.4%, as of 2015) and a group of plant biologists.