Al-Shamery Noah, Heppner Florian, Dosche Carsten, Morgenschweis Simon, Bredow Thomas, Wittstock Gunther, Lee Pooi See
School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.
Mulliken Center for Theoretical Chemistry, University of Bonn, Bonn, Germany.
Commun Chem. 2025 Aug 14;8(1):248. doi: 10.1038/s42004-025-01643-7.
Eumelanin is an interesting functional material for electrochemical applications due to its quinone/hydroquinone redox equilibrium. One major issue in the eumelanin film processing is the lack of solubility in polar solvents. In this study, the influence of functional groups of different polarity and their steric effects (tert-butyloxycarbonyl (Boc) groups giving "Mel-Boc" and nitro groups giving "Mel-NO") on the electrochemical properties of eumelanin in Zn coin cell devices is discussed. The derivatives are investigated using structural and surface analysis methods. Mel-Boc gives increased particle size and reduced capacity (0.97 mA h g at 0.4 A g) in aqueous electrolyte compared to synthetic eumelanin. This indicates the importance of high surface area and metal ion chelation in the polymers. Mel-NO shows improved water-solubility, cycling stability, improved capacity at current densities over 0.1 A g (19.5 mA h g at 0.2 A g), and good conductivity in ionic liquid electrolyte devices. Post-density functional theory calculations using a higher-level theoretical approach (meta-GGA level) compared to previous theoretical melanin investigations show the electron withdrawing nitro groups causing a reduced HOMO-LUMO gap potentially being a reason for the improved electrochemical properties.
由于其醌/对苯二酚氧化还原平衡，真黑素是一种用于电化学应用的有趣功能材料。真黑素薄膜制备中的一个主要问题是在极性溶剂中缺乏溶解性。在本研究中，讨论了不同极性的官能团及其空间效应（叔丁氧羰基（Boc）基团产生“Mel-Boc”，硝基产生“Mel-NO”）对锌硬币电池装置中真黑素电化学性能的影响。使用结构和表面分析方法对衍生物进行了研究。与合成真黑素相比，Mel-Boc在水性电解质中粒径增大且容量降低（在0.4 A g时为0.97 mA h g）。这表明聚合物中高表面积和金属离子螯合的重要性。Mel-NO在离子液体电解质装置中显示出改善的水溶性、循环稳定性、在电流密度超过0.1 A g时容量提高（在0.2 A g时为19.5 mA h g）以及良好的导电性。与之前的理论黑素研究相比，使用更高水平理论方法（meta-GGA水平）的密度泛函理论计算表明，吸电子硝基导致HOMO-LUMO能隙减小，这可能是电化学性能改善的一个原因。
