Systematic Investigation of the Physical and Electrochemical Characteristics of the Vanadium (III) Acidic Electrolyte With Different Concentrations and Related Diffusion Kinetics

Abstract

Owing to the lack of systematic kinetic theory about the redox reaction of V(III)/V(II), the poor electrochemical performance of the negative process in vanadium flow batteries limits the overall battery performance to a great extent. As the key factors that influence electrode/electrolyte interfacial reactivity, the physicochemical properties of the V(III) acidic electrolyte play an important role in the redox reaction of V(III)/V(II), hence a systematic investigation of the physical and electrochemical characteristics of V(III) acidic electrolytes with different concentrations and related diffusion kinetics was conducted in this work. It was found that the surface tension and viscosity of the electrolyte increase with increasing V(III) concentration, while the corresponding conductivity shows an opposite trend. Both the surface tension and viscosity change slightly with increasing concentration of H 2 SO 4 , but the conductivity increases significantly, indicating that a lower V(III) concentration and a higher H 2 SO 4 concentration are conducive to the ion transfer process. The electrochemical measurements further show that a higher V(III) concentration will facilitate the redox reaction of V(III)/V(II), while the increase in H 2 SO 4 concentration only improves the ion transmission and has little effect on the electron transfer process. Furthermore, the diffusion kinetics of V(III) have been further studied with cyclic voltammetry and chronopotentiometry. The results show that an elevated temperature facilitates the V(III)/V(II) redox reaction and gives rise to an increased electrode reaction rate constant ( k s ) and diffusion coefficient [ D V(III) ]. On this basis, the diffusion activation energy (13.7 kJ·mol −1 ) and the diffusion equation of V(III) are provided to integrate kinetic theory in the redox reaction of V(III)/V(II).

Identification of the Reduction Reaction Mechanism of V3+ on a Graphite Electrode in Acidic Solutions

“…Besides, the electrochemical reaction rate constants (k s ) and the formal potential (E O′ ) of the V 3+ /V 2+ redox reaction were obtained under the same test conditions in our previous work, 35 the corresponding values were shown in Table III.…”

“…In Eq. 3, A presents the apparent area of the electrode, D V 3+ is the diffusion coefficient of V 3+ , which has been obtained in our previous work, 35 and its value is 1.3*10 −7 cm 2 s −1 , v is the kinetic viscosity of the electrolyte used (0.01712 cm 2 s −1 from Ubbelohde viscometer) and C V 3+ is the bulk concentration of V 3+ . The value of n was calculated as 1.13 from the slope of the plot in Fig.…”

Treatment of carbon electrodes with Ti3C2Tx MXene coating and thermal method for vanadium redox flow batteries: a comparative study

“…When the baseline cannot be determined, the semiempirical method suggested by Nicholson is useful to estimate peak anodic current density ( j pa ) from peak cathodic current density ( j pc ), uncorrected peak current relative to the cathodic peak baseline ( j pa,0 ), and current density at switching potential, ( j sp,0 ). 45,46 …”

“…47 Therefore, the relationship between peak current density and diffusion coefficient is given by eqn (2), and the relationship with a reaction rate constant ( k 0 ) is given by Randles–Ševčík in eqn (3). 45,46 j p = (2.99 × 10 5 ) α 1/2 C b D 1/2 v 1/2 …”