Artificial photosynthesis learned from nature: Successfully developed new solar hydrogen production technology

Through joint research with Professor Hyojung Cha at the Department of Hydrogen and Renewable Energy, Kyungpook National University, Professor Park used the good nanosurface adsorption properties of tannic acid^[1]-based metal-polyphenol polymers to control the self-assembly and optical properties of fluorescent dyes while also identifying the photoexcitation^[2]and electron transfer mechanisms. Based on these findings, he implemented a solar-based biohydrogen production system using bacteria with hydrogenase enzymes.

During natural photosynthesis, chlorophyll absorbs light energy and transfers electrons to convert it into chemical energy. Artificial photosynthesis, which emulates this natural process of photosynthesis, uses sunlight to produce valuable resources, such as hydrogen, and it has garnered attention as a sustainable energy solution.

Professor Park's team developed a supramolecular photocatalyst that can transfer electrons similar to chlorophyll in nature by modifying rhodamine, an existing fluorescent dyes, into an amphiphilic structure. The team applied metal-polyphenol nano-coating technology based on tannic acid to improve performance and durability. Consequently, they demonstrated the production performance of approximately 18.4 mmol of hydrogen per hour per gram of catalyst under the visible spectrum. This performance is 5.6 times as high as that observed in previous studies using the same phosphor.

The research team combined their newly developed supramolecular dye with Shewanella oneidensis MR-1^[3], a bacterium capable of transferring electrons, to create a bio-composite system that converts ascorbic acid (vitamin C) into hydrogen using sunlight. The system operated stably for a long period and demonstrated its ability to produce hydrogen continuously.

Professor Park said, "This study marks an important achievement that reveals the specific mechanisms of organic dyes and artificial photosynthesis. In the future, I would like to conduct follow-up research on new supramolecular chemistry-based systems by combining functional microorganisms and new materials."

This study was funded by the Basic Research Laboratory Project and the Mid-Career Researcher Support Project under the National Research Foundation of Korea and the Alchemist Project under the Ministry of Trade, Industry and Energy, and its results (first author: Seokhyung Bu, PhD program student) were published in Angewandte Chemie International Edition.

^[1] Tannic acid: It is an eco-friendly material that can be easily obtained from coffee and tea, and its nanosurface can be coated through a simple process. It has a wide range of applications, including as photocatalysis and pollutant removal.

^[2] Photoexcitation: It refers to the process of exciting electrons in a substance to a higher energy state by using light energy (photons).

^[3] Shewanella oneidensis MR-1: It refers to a bacterium that is known for its ability to break down metals and minerals in nature. It is used in eco-friendly energy research, such as hydrogen production.