Derivados 1,4-naftoquinônicos no armazenamento de energia em baterias de fluxo redox: Utilização de ligações de hidrogênio intramoleculares para a modulação do potencial de redução de eletrólitos orgânicos

Abstract

To overcome the intermittency in energy generation from renewable sources such as solar and wind, the implementation of electrical energy storage systems, such as redox flow batteries (RFBs) have received great attention. Research for the development and use of organic species, such as quinones, has grown, since such species are abundant, can be extracted from natural sources, are chemically versatile and have a low cost. Quinones are redox active molecules with good electrochemical reversibility, easy synthetic modulation. It is extremely important to understand the chemical factors that interfere with its reduction potentials, and the formation of intra-and intermolecular bonds is a possible tool for the rational control of this property. When studying it, hydrogen bonding is a notorious possibility for modulating the electrochemical profile of quinones, obtaining more positive reduction potential values due to the increase in electrophilicity in its core. In this work, the formation of hydrogen bonds was explored as a tool for modulating the reduction potential in substituted naphthoquinones. The computational investigation demonstrated an efficient modulation of the reduction potential of both mono- and disubstituted derivatives with mercaptoethanol, leading to a weakening of the hydrogen bonds as the alkyl chain becomes longer. Nitrogenous derivative 82 showed no significant effect on the formation of intramolecular hydrogen bonding, due to the conjugation between the π electrons of the quinone nucleus and the pair of electrons of the nitrogen atom, disfavoring the interaction. However, experimentally, only compound 74 showed efficiency in modulating its redox potential, conjecturing that only one interaction per bond is taking place, as a terminal hydroxyl is blocked by the supporting electrolyte. In addition to demonstrating the modulation of the reduction potential of 74, such interaction justifies the effect not observed for the monosubstituted derivatives.