英国剑桥大学Scherman, Oren A.团队报道了耐空气氧化还原液流电池用缔合吡啶电解质。相关研究成果于2023年11月29日发表在国际知名学术期刊《自然》。

吡啶电解质是基于液流电池的能量存储的有前途的候选者。然而，它们的充放电过程和整体循环稳定性的机制仍知之甚少。

该文中，研究人员探索了吡啶电解质在代表性液流电池条件下的氧化还原行为，深入了解了含有这些电解质的电池的空气耐受性，同时提供了其可逆性的通用物理化学描述。利用扩展的双吡啶化合物的合成库，研究人员跟踪了它们在广泛电势范围内的性能，并将单线态-三线态自由能隙确定为一个描述符，该描述符成功地预测了先前未确定的容量衰减机制的开始。使用耦合操作核磁共振和电子顺磁共振光谱解释了这些电解质的氧化还原行为，并确定了电化学性能的两个不同区域（窄能隙和宽能隙）的存在。

在这两种情况下，研究人员将容量衰减与自由基物种的形成联系起来，并进一步表明π-二聚化在抑制这些自由基与溶解氧等微量杂质之间的反应性方面起着决定性作用。研究发现与围绕π-二聚体在氧化还原液流电池中的作用的主流观点形成了直接对比，使人们即使在长时间（天）暴露于空气中，也能有效缓解氧气对容量的衰减。这些见解为新的电解质系统铺平了道路，在该系统中，还原物种的反应性由其分子内和分子间自由基配对的倾向控制，从而能够在空气中操作。

附：英文原文

Title: Associative pyridinium electrolytes for air-tolerant redox flow batteries

Author: Carrington, Mark E., Sokoowski, Kamil, Jnsson, Erlendur, Zhao, Evan Wenbo, Graf, Anton M., Temprano, Israel, McCune, Jade A., Grey, Clare P., Scherman, Oren A.

Issue&Volume: 2023-11-29

Abstract: Pyridinium electrolytes are promising candidates for flow-battery-based energy storage1,2,3,4. However, the mechanisms underlying both their charge–discharge processes and overall cycling stability remain poorly understood. Here we probe the redox behaviour of pyridinium electrolytes under representative flow battery conditions, offering insights into air tolerance of batteries containing these electrolytes while providing a universal physico-chemical descriptor of their reversibility. Leveraging a synthetic library of extended bispyridinium compounds, we track their performance over a wide range of potentials and identify the singlet–triplet free energy gap as a descriptor that successfully predicts the onset of previously unidentified capacity fade mechanisms. Using coupled operando nuclear magnetic resonance and electron paramagnetic resonance spectroscopies5,6, we explain the redox behaviour of these electrolytes and determine the presence of two distinct regimes (narrow and wide energy gaps) of electrochemical performance. In both regimes, we tie capacity fade to the formation of free radical species, and further show that π-dimerization plays a decisive role in suppressing reactivity between these radicals and trace impurities such as dissolved oxygen. Our findings stand in direct contrast to prevailing views surrounding the role of π-dimers in redox flow batteries1,4,7,8,9,10,11 and enable us to efficiently mitigate capacity fade from oxygen even on prolonged (days) exposure to air. These insights pave the way to new electrolyte systems, in which reactivity of reduced species is controlled by their propensity for intra- and intermolecular pairing of free radicals, enabling operation in air.

DOI: 10.1038/s41586-023-06664-7

Source: https://www.nature.com/articles/s41586-023-06664-7