Biomimetic Reactive Oxygen Species (ROS) Scavenging System for Stability Enhancement of Thylakoid Membrane-Based Photosynthetic Biosolar Cells

Since photosynthesis of plants has a high quantum yield close to 100%, many studies have been conducted to utilize the photosynthesis for bio-energy harvesting using algal cells, chloroplasts, thylakoid membranes (TMs), and isolated photosystems (PS I, II). The extracted photosynthetic organelles are preferred among these for their direct contact with the electrode and easier transfer of photosynthetic electrons (PEs). However, under high light intensity, reactive oxygen species (ROS) are generated during photosynthesis, causing damage to lipid membranes or proteins. Therefore, for long-term stability, a closed system capable of scavenging ROS like chloroplasts is required. In this study, we propose a biomimetic ROS scavenging system for stability enhancement of bio-solar cells. We used catalase to scavenge ROS, which causes the damage to extracted photosynthetic organelles and apparatuses. As a popular extracted photosynthetic organelle, TMs were used for bioenergy harvesting, and an artificial independent closed environment that did not interfere with PEs transport was constructed using alginate as extracellular matrix and the Nafion membrane. First, dye release test and catalase assay either in the presence or absence of Nafion membrane were performed to measure the leakage of catalase. The tests confirmed that the release of dye and catalase from the film coated with the Nafion membrane was negligible. However, the Nafion solution used for coating contains aliphatic alcohol that can damage lipid membranes or proteins. To analysis the effect of alcohol on TMs, photocurrents from TMs for different ethanol concentrations used in Nafion membrane wer measured. TMs treated with 5% ethanol concentration produced about 82% of photocurrents from the non-treated TMs. Therefore, it was concluded that a sufficiently diluted Nafion solution did not significantly affect the production of TM photocurrent. Based on this, a 10-fold diluted Nafion solution was used for the coating of TM/alginate mixture film containing catalase. Furthermore, the film fabrication conditions were optimized through the photocurrent results according to the ratio among TMs, alginate, and catalse. Finally, in order to confirm the stability improvement of a photosynthetic bio-solar cell by catalase encapsulated system, the photocurrent from the system was observed for 5 hours under AM 1.5G (1 sun = 100 mW/cm²) illumination at intervals of 1,000 s. Afterwards, the stability improvement was evaluated by comparing the initial photocurrent and the photocurrent after 5 hours illumination. As a result, it was confirmed that about 4.3 times improved stability was achieved by the biomimetic ROS scavenging system.<br/><br/><br/>REFERENCES<br/>[1] Khorobrykh, Sergey A., Maarit Karonen, and Esa Tyystjärvi. FEBS letters 589.6 (2015): 779-786.<br/>[2] Sjöholm, Kyle H., Michelle Rasmussen, and Shelley D. Minteer. ECS Electrochemistry Letters 1.5 (2012): G7.<br/>[3] Pankratov, Dmitry, Galina Pankratova, and Lo Gorton. Current Opinion in Electrochemistry 19 (2020): 49-54.