期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：9
DOI：10.1073/pnas.2114947119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
The current study investigates fundamentals of electrochemical reactions using the membrane-free redox flow battery (RFB) platform with a laminar strategy and colorimetry of multiredox organic molecules. Taking advantage of unique color changes of electrolytes depending on the state of charge, we analyze the electrochemical kinetics of the RFB system in terms of charge and mass transfer. It is verified that a balanced rate of charge and mass transfer significantly affects the battery performance. Furthermore, a classical physicochemical hydrodynamic equation is adopted for scaling analysis of the depletion region deteriorating battery performance. We successfully integrate analytical, numerical, and experimental data for elucidating the depletion region. Based on these fundamental studies, finally, a favorable design is suggested for performance enhancement.
Redox flow batteries (RFBs) are attractive large-scale energy storage techniques, achieving remarkable progress in performance enhancement for the last decades. Nevertheless, an in-depth understanding of the reaction mechanism still remains challenging due to its unique operation mechanism, where electrochemistry and hydrodynamics simultaneously govern battery performance. Thus, to elucidate the precise reactions occurring in RFB systems, an appropriate analysis technique that enables the real-time observation of electrokinetic phenomena is indispensable. Herein, we report in operando visualization and analytical study of RFBs by employing a membrane-free microfluidic platform, that is, a membrane-free microfluidic RFB. Using this platform, the electrokinetic investigations were carried out for the 5,10-bis(2-methoxyethyl)-5,10-dihydrophenazine (BMEPZ) catholyte, which has been recently proposed as a high-performance multiredox organic molecule. Taking advantage of the inherent colorimetric property of BMEPZ, we unravel the intrinsic electrochemical properties in terms of charge and mass transfer kinetics during the multiredox reaction through in operando visualization, which enables theoretical study of physicochemical hydrodynamics in electrochemical systems. Based on insights on the electrokinetic limitations in RFBs, we verify the validity of electrode geometry design that can suppress the range of the depletion region, leading to enhanced cell performance.
