A composite electrode with gradient pores for high-performance aqueous redox flow batteries. (May 2023)

• Record Type: Journal Article
• Authors: Zhang, Zhihui; Zhang, Baowen; Wei, Lei; Lei, Yuan; Bai, Bofeng; Chen, Liuping; Xu, Junhui; Zhao, Tianshou
• Is Part Of: Journal of energy storage. Volume 61(2023)
• Publication Date: 2023-05
• Subjects: Vanadium flow battery -- Gradient porosity -- Surface area -- Mass transport -- Efficiency; Energy storage -- Periodicals; Energy storage -- Research -- Periodicals; 621.3126
• DOI: 10.1016/j.est.2023.106755
• Languages: English
• ISSNs: 2352-152X

Abstract

Abstract: Large surface areas while maintaining a low mass transport resistance is a critical criterion for the optimal design of electrode structures for aqueous redox flow batteries. However, for conventional micro-scale electrode structures, increasing surface areas will lead to an increase in the mass transfer resistance. In this work, a composite electrode with a gradient porosity distribution is fabricated through combining two different carbon felt layers of different porosities. The smaller-porosity layer, offering a larger surface area, is placed adjacent to the membrane, while the larger-porosity layer, providing a smaller mass transfer resistance is placed on the flow field side. The thickness ratio of the two layers is adjusted in terms of the battery performance while applied in the vanadium redox flow battery. It is demonstrated that the battery with the structure-optimized composite electrode achieves a high energy efficiency of 82.7 % at 200 mA·cm −2 at an electrolyte flow rate of 30 mL·min −1, and delivers a discharge capacity of 240 mAh at 400 mA·cm −2, which is 2.18 times that of the conventional graphite felt electrode. This work offers an idea for the structural design of high-performance aqueous redox flow batteries. Highlights: The electrodes combined by two carbon felt layer with different porosities are prepared for vanadium redox flow batteries. The composite electrode has the advantage of fast transportation property and large reaction surface area for vanadium ions. The battery with composite electrode shows an energy efficiency of 82.7% at 200 mA cm -2 at 30 mL·min -1 . The battery with composite electrode shows higher discharge capacity, capacity retention rate and better cycle stability.