Electrochemical Performance Of Positive Electrolyte For Vanadium Redox Battery And Organic Redox Flow Battery

The electrolyte of vanadium redox flow batteries, which is not only acting as the conductor of the ion but also the energy-storage medium, determined the overall performance of the batteris. To improve the electrochemical performances and thermal stability of the positive electrolyte of vanadium flow batteries, methanesulfonic acid was used as the supporting electrolyte. At the same time, combined the advantages of electroactive organic compounds and redox flow batteries, a novel "all-organic redox flow battery"(AORFB) is proposed. The main points can be summarized as follows:(1) Electrolyze vanadium electrolyte using methanesulfonic acid as supporting electrolyte by different electrode. The coulombic efficiency of electrolysis using graphite-graphite felt as electrode is higest. Analysis the electroactive of the electrolyte electrolyzed by different electrode, it can be found that the electrolyte electrolyzed by graphite-graphite felt is batter than others. Cyclic voltammetry shows a pair of redox peaks, the peak potential separation is82mV, the peak current is high (52.5mA) which denote the fast electrode reaction kinetic. And the charge-discharge characteristics of this electrolyte are best.(2) The electrochemical properties of2mol/L V(IV) dissolved in H2SO4and methanesulfonic acid were investigated by electrochemical measurements. From these tests, it can be found that the electrochemical properties of2mol/L V(IV) dissolved in7mol/L methanesulfonic acid is best. From the cyclic voltammetry tests the peak potential separation is82mV, the diffusion coefficient is in the range of (0.94-1.52)×10-6cm2/s. The charge transfer resistance (5.61Ω), the exchange current density (4.57×10-3A/cm2), the standard electrode reaction rate constant (4.74×10-5cm/s) are calculated by the test of polarization curve. Stable charge-discharge curves and high voltage efficiency and energy efficiency are obtained. And it can be found that the thermal stability of2mol/L V(V) dissolved in7mol/L MSA is better than the electrolyte using H2SO4as supporting electrolyte.(3) A novel all-organic redox flow battery employing2,2,6,6-tetramethyl-1-piperidinyloxy/NaClO4/acetonitrile and N-Methylphthalimide/NaClO4/acetonitrile as catholyte and anolyte, respectively, is investigated by electrochemical measurements. The quasi-reversible and stable redox reactions are tested by cycle voltammetry. The diffusion coefficient of N-Methylphthalimide and2,2,6,6-tetramethyl-1-piperidinyloxy in the electrolyte are in the range of (0.66-1.06)×10-5cm2·s-1and (0.67-1.09)×10-5cm2·s-1at room temperature, respectively. Stable charge-discharge curves and high coulombic efficiency (90%) for the first20cycles are obtained.