Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstrasse 10, 07743 Jena, Germany.
Center for Energy and Environmental Chemistry Jena (CEEC Jena), Friedrich Schiller University Jena, Philosophenweg 7a, 07743 Jena, Germany.
Molecules. 2021 Jun 23;26(13):3823. doi: 10.3390/molecules26133823.
Owing to their broad range of redox potential, quinones/hydroquinones can be utilized for energy storage in redox flow batteries. In terms of stability, organic catholytes are more challenging than anolytes. The two-electron transfer feature adds value when building all-quinone flow battery systems. However, the dimerization of quinones/hydroquinones usually makes it difficult to achieve a full two-electron transfer in practical redox flow battery applications. In this work, we designed and synthesized four new hydroquinone derivatives bearing morpholinomethylene and/or methyl groups in different positions on the benzene ring to probe molecular stability upon battery cycling. The redox potential of the four molecules were investigated, followed by long-term stability tests using different supporting electrolytes and cell cycling methods in a symmetric flow cell. The derivative with two unoccupied ortho positions was found highly unstable, the cell of which exhibited a capacity decay rate of ~50% per day. Fully substituted hydroquinones turned out to be more stable. In particular, 2,6-dimethyl-3,5-bis(morpholinomethylene)benzene-1,4-diol () displayed a capacity decay of only 0.45%/day with four-week potentiostatic cycling at 0.1 M in 1 M HPO. In addition, the three fully substituted hydroquinones displayed good accessible capacity of over 82%, much higher than those of conventional quinone derivatives.
由于醌/氢醌具有广泛的氧化还原电位，因此可用于氧化还原液流电池的储能。在稳定性方面，有机阴极比阳极更具挑战性。在构建全醌液流电池系统时，两电子转移特性具有附加价值。然而，醌/氢醌的二聚化通常使得在实际氧化还原液流电池应用中难以实现完全的两电子转移。在这项工作中，我们设计并合成了四个新的带有吗啉基亚甲基和/或甲基的氢醌衍生物，它们在苯环的不同位置上取代，以探究电池循环过程中分子的稳定性。研究了这四个分子的氧化还原电位，然后使用不同的支持电解质和电池循环方法在对称流电池中进行了长期稳定性测试。具有两个未占据的邻位的衍生物被发现极不稳定，其电池的容量衰减率约为每天 50%。完全取代的氢醌则更为稳定。特别是，2,6-二甲基-3,5-双(吗啉基亚甲基)苯-1,4-二醇（）在 0.1 M 的 1 M HPO 中以 0.1 M 的电势循环时，具有仅为 0.45%/天的容量衰减，经过四周的恒电势循环。此外，这三个完全取代的氢醌显示出超过 82%的良好可及容量，远高于常规醌衍生物。
