Asymmetric batteries based on customized positive and negative electrodes-an effective strategy to further improve the performance of vanadium redox flow batteries.

• Individualized customization of electrodes in VRFBs is realized by electrospinning. • Both positive and negative electrode reaction kinetics have been improved. • Dynamical difference of the electrode reactions in VRFBs has been reduced. • Asymmetric VRFB shows superior performance. There are significant differences in the cathodic and anodic kinetics of vanadium redox flow batteries (VRFBs), thus the use of a single composition and structure of electrode materials is unbefitting according to the barrel principle. Herein, W and Sb based electrocatalysts are evenly embedded into the electrospun carbon nanofibers (ECNFs), and the active functional groups and surface defects of the W-ECNFs and Sb-ECNFs electrodes are increased effectively, which resulted in a significant improvement in their hydrophilicity, specific surface area and electrocatalytic activity towards the VO 2 +/VO2+ and V3+/V2+redox reactions. The electrode reaction rate constant k and diffusion coefficient D of the positive and negative reactions on W-ECNFs and Sb-ECNFs are more similar and closely matched, which is more conducive to the effective improvement of battery performance. As a results, the asymmetric battery with W-ECNFs and Sb-ECNFs as positive and negative electrode shows the highest energy efficiency of 81.33% at 200 mA/cm2, higher than that of the VRFBs with pristine ECNFs as both two electrodes (75.66%) or that only optimizing one electrode (79.76% and 78.15%). The excellent battery performance further verifies the feasibility of constructing asymmetric batteries according to the difference of the positive and negative reaction kinetics in VRFBs. [Display omitted] The gap between anode and cathode reaction kinetics is closed by individualized customization of the anode and cathode electrode materials in a VRFB, and the battery performance is improved more significantly due to the asymmetric structure design. [ABSTRACT FROM AUTHOR]