Electrochemical Processes Unit , IMDEA Energy Institute , Avda. Ramón de la Sagra 3 , 28935 Móstoles , Spain.
Chemical and Environmental Engineering Group , Rey Juan Carlos University , C/Tulipán s/n , 28933 Móstoles , Madrid , Spain.
ACS Appl Mater Interfaces. 2018 Dec 5;10(48):41246-41256. doi: 10.1021/acsami.8b11581. Epub 2018 Nov 20.
Lately, the field of redox flow batteries is flourishing because of the emergence of new redox chemistries, including organic compounds, new electrolytes, and innovative designs. Recently, we reported an original membrane-free battery concept based on the mutual immiscibility of an aqueous catholyte containing hydroquinone and an ionic liquid anolyte containing para-benzoquinone as redox species. Here, we investigate the versatility of this concept exploring the electrochemical performance of 10 redox electrolytes based on different solvents, such as propylene carbonate, 2-butanone, or neutral-pH media, and containing different redox organic molecules, such as 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine1-oxyl (OH-TEMPO), or substituted anthraquinones. The most representative electrolytes were paired and used as immiscible anolyte-catholyte in 5 different membrane-free batteries. Those batteries with substituted anthraquinones in the anolyte exhibited up to 50% improved open-circuit voltage (2.1 V), an operating voltage of 1.75 V, and 62% higher power density compared with our previous work. On the other hand, the partition coefficient of redox molecules between the two immiscible phases and the inherent self-discharge occurring at the interphase are revealed as intrinsic features affecting the performance of this type of membrane-free battery. It was successfully demonstrated that the functionalization of redox molecules is an interesting strategy to tune the partition coefficients mitigating the crossover that provokes low battery efficiency. As a result, the cycling life of a battery having OH-TEMPO as active species in the catholyte and containing propylene carbonate-based anolyte was evaluated over 300 cycles, achieving 85% capacity retention. These results demonstrated the huge versatility and countless possibilities of this new membrane-free battery concept.
最近，由于新的氧化还原化学物质的出现，包括有机化合物、新型电解质和创新设计，氧化还原流电池领域蓬勃发展。最近，我们报道了一种基于水相阴极液中含有对苯二酚和离子液体相阳极液中含有对苯醌的互不相容性的原始无膜电池概念。在这里，我们通过探索基于不同溶剂（如碳酸丙烯酯、2-丁酮或中性 pH 介质）和不同氧化还原有机分子（如 2,2,6,6-四甲基哌啶-1-氧自由基、4-羟基-2,2,6,6-四甲基哌啶-1-氧自由基（OH-TEMPO）或取代蒽醌）的 10 种氧化还原电解质的电化学性能，研究了该概念的多功能性。最具代表性的电解质进行配对，并用作 5 种不同无膜电池中的不混溶阳极-阴极电解液。那些在阳极中含有取代蒽醌的电解质的开路电压（2.1V）提高了 50%，工作电压为 1.75V，与我们之前的工作相比，功率密度提高了 62%。另一方面，揭示了氧化还原分子在两相之间的分配系数和界面处发生的固有自放电是影响这种无膜电池性能的内在特征。成功地证明了氧化还原分子的功能化是一种调节分配系数的有趣策略，可以减轻引起电池效率降低的交叉。结果，在含有基于碳酸丙烯酯的阳极的阴极液中含有 OH-TEMPO 作为活性物质的电池的循环寿命超过 300 次，容量保持率达到 85%。这些结果表明了这种新型无膜电池概念的巨大多功能性和无数可能性。
