Effect of different additives with –NH2 or –NH4+ functional groups on V(V) electrolytes for a vanadium redox flow battery

•The V(V) electrolytes with the addition of organic amines CTS, SA and NPAM and inorganic ammonium ATC, FAS and AFS remained stable from − 5 °C to 45 °C.•The electrochemical activity for V(V) electrolytes with the addition of CTS, ATC, AFS and FAS was improved compared with the pristine one.•Overall, the effect of the organic amines on the V(V) solution was better than the inorganic ammoniums.•The VRB with CTS performed well with an energy efficiency of more than 80% and good cycling stability at a current density of 50 mAcm− 2.

Several organic amines with –NH2 functional groups and inorganic ammoniums with –NH4+ functional groups have been comparatively investigated as stabilizers of the V(V) electrolyte for vanadium redox flow battery (VRB) to improve its stability and electrochemical performance. Thermal stability tests showed that chitosan (CTS) and nonionic-type polyacrylamide (NPAM) additives with –NH2; ammonium thiocyanate (ATC), ferrous ammonium sulfate (FAS) and ammonium ferric sulfate (AFS) additives with –NH4+ could significantly improve the thermal stability of the V(V) electrolyte over a wide temperature range of − 5 °C to 45 °C. The electrochemical behavior of the V(V) electrolyte with these preferred additives was further studied by cyclic voltammetry (CV), steady state polarization, electrochemical impedance spectroscopy (EIS) and charge–discharge test. The results indicated that the electrochemical activity and reversibility for the V(V) electrolyte with the best additive CTS with –NH4+ was significantly improved compared with the additives with –NH2 and pristine one. In addition, the VRB employing the positive electrolyte with CTS exhibited excellent cycling stability and charge–discharge behavior with a high energy efficiency of 82.5%. The N-containing and O-containing functional groups of CTS in the V(V) electrolyte could modify the electrode and further improve the electrochemical performance and cycling stability of VRB.

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