Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2022 Mar 1;119(9):e2114947119.
doi: 10.1073/pnas.2114947119.

In operando visualization of redox flow battery in membrane-free microfluidic platform

Affiliations

In operando visualization of redox flow battery in membrane-free microfluidic platform

Hyungjoo Park et al. Proc Natl Acad Sci U S A. .

Erratum in

Abstract

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.

Keywords: electrochemistry and hydrodynamics; in operando visualization; in-depth study; membrane-free redox flow battery; multiredox organic molecule.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
(A) The microscale fabrication process of the MFRFB device. (B) Photo of an assembled MFRFB device connected to an electrical source; GND, xyz. (C) Microscopic view of the observation area for the current study. (D) Experimental setup of the in operando visualization experiment. The setup consisted of an MFRFB device on the microscope, a syringe pump, a source measure unit, and a desktop for recording images.
Fig. 2.
Fig. 2.
(A) The cyclic voltammetry of the redox couple of BMEPZ/FL. (B) Voltage and capacity profiles of MFRFB using the redox couple of BMEPZ/FL in terms of charge transfer. (C) In operando visualization of the electrochemical reaction in terms of charge transfer. (D) Voltage and capacity profiles of the MFRFB using the redox couple of BMEPZ/FL in terms of mass transfer. (E) In operando visualization of electrochemical reaction in terms of mass transfer.
Fig. 3.
Fig. 3.
(A) Schematic of the MFRFB and theoretical regions that affect battery performance. (B) Numerical results of concentration profiles of BMEPZ, BMEPZ+, BMEPZ2+, and FL at the low-current density. (C) Numerical results of concentration profiles of BMEPZ, BMEPZ+, BMEPZ2+, and FL at the high-current density. (D) Image of scaling analysis for the concentration boundary layer of BMEPZ2+ at a flow rate of 10 μL min−1 and a current of 0.14 mA; i, ii, iii, and iv indicate the four windows. (E) Comparison of experimental, numerical, and analytical slopes of the concentration boundary layer relation.
Fig. 4.
Fig. 4.
(A) Comparison of electrochemical performance with respect to the geometric configuration of the electrode. (B) Phase diagram of the required minimum flow rate to make mixing of reactants negligible during one flow depending on the aspect ratio of cells for various active materials in RFBs with corresponding diffusion coefficients; 4HO-TEMPO, BMEPZ, DHAQ, CoCP2, Vanadium.

References

    1. Badwal S. P. S., Giddey S. S., Munnings C., Bhatt A. I., Hollenkamp A. F., Emerging electrochemical energy conversion and storage technologies. Front Chem. 2, 79 (2014). - PMC - PubMed
    1. Larcher D., Tarascon J. M., Towards greener and more sustainable batteries for electrical energy storage. Nat. Chem. 7, 19–29 (2015). - PubMed
    1. Park M., Ryu J., Wang W., Cho J., Material design and engineering of next-generation flow-battery technologies. Nat. Rev. Mater. 2, 16080 (2017).
    1. Winsberg J., Hagemann T., Janoschka T., Hager M. D., Schubert U. S., Redox-flow batteries: From metals to organic redox-active materials. Angew. Chem. Int. Ed. Engl. 56, 686–711 (2017). - PMC - PubMed
    1. Lee S., et al. , Recent progress in organic electrodes for Li and Na rechargeable batteries. Adv. Mater. 30, e1704682 (2018). - PubMed

LinkOut - more resources