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Han Zhiji's Research Group: Anthraquinone Organic Dyes for Efficient Catalytic Hydrogen Production from Low-Energy Light - Sun Yat-sen University News Website

**Abstract:** Over the past century, the excessive extraction and consumption of fossil fuels have led to a rapid increase in global carbon dioxide levels, posing significant environmental challenges. Addressing these issues and achieving the dual carbon goals (carbon peak and carbon neutrality) is a critical task for researchers worldwide. Inspired by natural photosynthetic systems, scientists have developed artificial photosynthetic systems to convert solar energy into clean, renewable energy. However, a considerable portion of the solar spectrum, particularly the long-wavelength light (280–600 nm), which accounts for less than 20% of the sunlight reaching Earth's surface, remains underutilized. Red light, in particular, is crucial for driving photocatalytic proton reduction, a key step in energy conversion. Recently, Professor Han Zhiji's research group at the School of Chemistry, Sun Yat-sen University, has reported a significant advancement in the use of anthraquinone organic dyes for red-light-driven hydrogen production. This novel system employs low-cost anthraquinone dyes as photosensitizers and cobalt complexes as non-precious metal catalysts, achieving remarkable stability and efficiency under red light conditions. The system demonstrated a stability of up to 168 hours, primarily limited by the complete consumption of electron donors in the solution. It achieved a catalytic turnover number (TON) of 780,000 and a turnover frequency (TOF) exceeding 7,000 per hour, with a quantum efficiency of over 30%. These performance metrics rank it among the best red-light-driven artificial photosynthetic hydrogen production systems reported to date. The anthraquinone dyes, which are among the oldest and most abundant natural dyes, exhibit stable redox properties and strong wavelength tunability, making them ideal candidates for this application. The key to the system's high efficiency and stability lies in the unique excited state of the photosensitizer (DAHA), its stable redox behavior, and the ultra-fast rate of photogenerated electron and electron transfer. The mechanism of hydrogen production involves the dye absorbing solar energy, which leads to the formation of a triplet excited state. This state is then reduced and protonated, resulting in the effective reduction of the cobalt catalyst and the subsequent formation of intermediates such as CoI, CoIII-H, and CoII-H. Ultimately, these intermediates react with protons to generate hydrogen gas. This research provides a new approach for utilizing the full solar spectrum in various photocatalytic reactions, potentially enhancing the overall efficiency of solar energy conversion. The findings are particularly significant in the context of developing sustainable and cost-effective methods for hydrogen production, which is a crucial component of the global effort to transition to renewable energy sources. The study, titled "Efficient Red-Light-Driven Hydrogen Evolution with an Anthraquinone Organic Dye," was published in the Journal of the American Chemical Society. Professor Han Zhiji is the corresponding author, and Ming Mei, a 2019 doctoral student at the School of Chemistry, is the first author. The paper can be accessed at: https://doi.org/10.1021/jacs.2c08171. **Key Elements:** - **Problem Addressed:** The environmental impact of fossil fuel consumption and the need for efficient, renewable energy sources. - **Solution Proposed:** Development of an artificial photosynthetic system using anthraquinone organic dyes and non-precious metal cobalt catalysts. - **Key Achievements:** High stability (168 hours), high catalytic turnover number (780,000), high turnover frequency (over 7,000 per hour), and quantum efficiency (over 30%) under red light conditions. - **Mechanism:** The system's efficiency is attributed to the unique excited state of the photosensitizer, stable redox properties, and rapid electron transfer. - **Significance:** This approach could enhance the utilization of the full solar spectrum in photocatalytic reactions, advancing the field of renewable energy and hydrogen production. - **Publication:** The research was published in the Journal of the American Chemical Society, with Professor Han Zhiji as the corresponding author and Ming Mei as the first author.

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