Effects Of Pyridine Carboxylic Acid On The Positive Electrolyte For Vanadium Redox Flow Battery

In this thesis, the research work was focusd on the thermal stability and electrochemical activity of positive electrolyte. Pyridine carboxylic acid were used as additives for the positive electrolyte of vanadium redox battey. The amount and site of carboxylic acid were compared and the stability mechanism were probed. The main points can be summarized as following:(1)2-picolinic acid and2,6-pyridinedicarboxylic acid have been individually used as additives in positive electrolyte containing2.0mol·L-1VOSO4and3.0mol·L-1H2SO4for all-vanadium redox flow batteries. The effects of each additive on positive electrolyte were compared. The thermal stability tests showed that2,6-pyridinedicarboxylic acid had superior improvement than2-picolinic, without changing the valance state of V(V) ions. At40℃, the initial setting time of V(V) electrolyte is60%longer than pristine electrolyte. Zeta potential indicate that adding additive can adsorb on V(V) ions or interaction with V(V) ions to increase the electrostatic repulsion between the V(V) ions in the bulk solution. Raman spectra further demonstrated that2,6-pyridinedicarboxylic acid can react with V(V) ions by replacing SO42-/HSO4-, and on the other hand reducing the polymerization of V(V) ions. Cyclic voltammetry(CV) results suggested that the addition2,6-pyridinedicarboxylic acid has no negative effects on the electrolyte activity of positive electrolyte.(2) Changing the position of carboxylic group,2,3-Pyridinedicarboxylic acid and2,6-pyridinedicarboxylic acid were used as additive in positive electrolyte. The effects of each additive on the thermal stability and electrochemical properties of the positive electrolyte were investigated. The thermal stability tests showed that the both additions can delay the precipitation of V2O5in the electrolyte. Cyclic voltammetry (CV) and Linear Sweep Voltammetry (LSV) results suggested that the electrochemical reversibility of V(IV)/V(V) redox couple in the electrolyte can be improved by the addition of2,3-Pyridinedicarboxylic acid. The diffusion coefficient of V(IV) increased from0.36～0.56×10-6cm2s-1to0.57～0.89×10-6cm2s-1after adding1mol%2,3-Pyridinedicarboxylic acid, and the reaction rate constant (Ko) of VO2+/VO2+couple increased19.86%. The average energy efficiency of cells employing the electrolyte with1mol%2,3-Pyridinedicarboxylic acid reached74.88%,1.02%higher than that of the pristine electrolyte. XPS measurement indicated that the enhancement of electrochemical performance is due to the absorption of2,3-Pyridinedicarboxylic acid on the surface of surface of electrode, providing more active sites to facilitate the electron transfer on electrode/electrolyte interface.