A High-Performance Bismuth Decorated Carbon Cloth Electrode for Vanadium Redox Flow Batteries

Abstract

The fluctuated and intermittent nature of renewable energies, such as solar energy and wind energy, presents an imperative need to develop reliable, efficient and cost-effective large scale energy storage systems. Among the state-of-art large scale energy storage technologies, vanadium redox flow batteries (VRFBs) attract the most attention due to the advantages of decoupling power and energy, excellent electrochemical reversibility, no cross-contamination and long cycle life [1,2]. Even though, the widespread application of VRFBs is still hindered by the high capital cost, mostly resulting from the large stack size and precious redox-active materials [3]. In this regard, a VRFB capable of operating at high current density with deep charge/discharge depth is highly desirable, because the improved current density and charge/discharge depth will lead to the reduced stack size and the increased usage of electrolyte, respectively. However, the high current density would inevitably increase the cell polarization, resulting in the declining battery efficiency as well as electrolyte utilization. As a critical component of VRFBs system, the electrode exerts a significant influence on the battery performance since it contributes to the system polarization through not only the ohmic polarization, but also the activation polarization and concentration polarization. Thus, an idea electrode for VRFBs should have high surface activity and specific surface area to decrease activation loss, high electrical conductivity to decrease ohmic loss and high hydraulic permeability to decrease concentration loss [4]. In this work, a high-performance bismuth decorated carbon cloth electrode is prepared for VRFBs. Due to the thin thickness, low tortuosity and broad pore distribution ranging from 5 to 100 μm [5], carbon cloth electrode shows low electrical resistance and high permeability. In addition, the electrodeposited bismuth can effectively catalyze the vanadium redox reactions to increase the surface activity [6]. Our preliminary results show that the battery assembled with the present electrode delivers a high energy efficiency over 80 % at the high current density of 320 mA cm-1 for more than 100 cycles. Further experimental results will be disclosed at the meeting.