The catalytic effect of bismuth for VO2+/VO2+ and V3+/V2+ redox couples in vanadium flow batteries
Xiaofei Yanga,b, Tao Liua, Chi Xua,b, Hongzhang Zhanga,c, Xianfeng Lia,c, Huamin Zhanga,c
a Division of Energy Storage, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China;
b University of Chinese Academy of Sciences, Beijing 100039, China;
c Collaborative Innovation Center of Chemistry for Energy Materials(iChEM), Dalian 116023, Liaoning, China
摘要 The effect of bismuth (Bi) for both VO2+/VO2+ and V3+/V2+ redox couples in vanadium flow batteries (VFBs) has been investigated by directly introducing Bi on the surface of carbon felt (CF). The results show that Bi has no catalytic effect for VO2+/VO2+ redox couple. During the first charge process, Bi is oxidized to Bi3+ (never return back to Bi metal in the subsequent cycles) due to the low standard redox potential of 0.308 V (vs. SHE) for Bi3+/Bi redox couple compared with VO2+/VO2+ redox couple and Bi3+ exhibit no (or neglectable) electro-catalytic activity. Additionally, the relationship between Bi loading and electrochemical activity for V3+/V2+ redox couple was studied in detail. 2 wt% Bi-modified carbon felt (2%-BiCF) exhibits the highest electrochemical activity. Using it as negative electrode, a high energy efficiency (EE) of 79.0% can be achieved at a high current density of 160 mA/cm2, which is 5.5% higher than the pristine one. Moreover, the electrolyte utilization ratio is also increased by more than 30%. Even the cell operated at 140 mA/cm2 for over 300 cycles, the EE can reach 80.9% without obvious fluctuation and attenuation, suggesting excellent catalytic activity and electrochemical stability in VFBs.
The authors greatly acknowledge the financial support from the China Natural Science Foundation (Grant nos. 51403209, 21406221, 21206158, 21476224, 21406219 and 51361135701) and the Outstanding Young Scientist Foundation, Chinese Academy of Sciences (CAS), Supported by the Key Research Program of the Chinese Academy of Sciences (KG2D-EW-602-2), Science and Technology Service Network Initiative (KFJ-EW-STS-108), Dalian Municipal Outstanding Young Talent Foundation (2014J11JH131).