Progress in Research of Photoelectrochemical System Based on Water/Oxygen Cycle for Solar Energy Transformation and Storage

As the most extensive renewable energy (23,000 TW/year) in nature, how to realize its efficient and reasonable development and utilization has always been a research hotspot for scientific researchers. From the current development stage, the utilization of solar energy mainly focuses on three aspects: solar power system, solar thermal system, and solar fuel system. However, the intermittent problem of regional light source caused by Earth rotation greatly limits the continuous conversion of solar energy to other energy sources, so that it cannot meet the continuous energy demand in daily production and life. In response to the problem, scientists put forward the corresponding energy reserve strategy. By combining the photoelectrochemical system with the secondary cell or liquid flow cell system, the conversion and storage of solar energy are realized, and the energy supply and demand caused by the intermittent light source are effectively solved. However, the multi-system connection has the disadvantages of complex systems, high cost, and serious energy transmission loss. Therefore, how to design the integrated solar energy storage system rationally has become the next research problem that researchers need to solve.     Recently, Shaojun Dong’s team at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences realized the continuous transformation and storage of solar energy under an integrated system by constructing a bio-photoelectrochemical model based on water/oxygen circulation, providing a new research idea for the efficient use of renewable energy.   The team designed the bio-photochemical system to use polypyrrole solid-state capacitive electrodes as energy storage modules to make the energy storage process safer and easier. In the process of solar energy storage, the water/oxygen molecules in the system can spontaneously form a cycle without the participation of additional sacrifice reagents and other redox pairs, which greatly improves the safety of the equipment and reduces the cost.   In addition, the modular and integrated structural design of this system enables it to be adjusted and optimized according to different circumstances and better meet the practical application needs of many aspects. Experimental data analysis showed that the conceptual model obtained maximum power density outputs of 0.34 ± 0.01 and 0.19 ± 0.02 mWcm-2 under light and darkfield conditions, respectively, and showed stable solar accumulator cycle performance. By changing the capacitance of the energy storage module (polypyrrole capacitive electrode), the charge/discharge time can be effectively regulated. In this research work, the construction of the bio-photoelectrochemical model of water/oxygen cycle promotes the development of cross-integration among photoelectrochemical systems, bioelectrochemical systems, and capacitor systems on the one hand, and also provides certain guiding significance for the future research and development of green rechargeable devices on the other hand. The results were recently published in the Journal of the American Chemical Society, (2019, 141, 16416-16421), and were supported by the National Natural Science Foundation of China and the Ministry of Science and Technology of China.