KINETIC STUDY OF THE FERROCENE COMPLEX IN BINARY IONIC LIQUID MEDIA

• Main Author: Salendra, Alvin
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/63784
• Institution: Institut Teknologi Bandung

Ionic liquids are molten liquids at low temperatures with good thermal and electrochemical stability. It makes ionic liquids widely applied as electrolytes in various energy storage devices such as batteries. However, its relatively low conductivity of conventional solvents hinders the ion transfer process. To overcome this problem, one way that can be done is to design a binary ionic liquid to obtain the target's desired physical and chemical properties. The research aimed at increasing the conductivity of the ionic liquid [bmim][PF6] with the addition of [bmim][TFSI] was carried out in various mole fractions 0; 0.25; 0.50; 0.75; 1 at a temperature of 303 – 323 K. Based on the results of the research conducted, it is known that the ionic conductivity values (?) of ionic liquids [bmim][PF6] and [bmim][TFSI] as measured using Electrochemical Impedance Spectroscopy (EIS) are respectively 2.12 and 4.75 mS.cm-1 at 303 K. The addition of [bmim][TFSI] overall increased the conductivity of [bmim][PF6] in proportion to the amount added. Furthermore, the kinetic aspect on the electrode surface is also studied, considering that the performance of ionic liquids as electrolytes is influenced by mass and charge transfer when interacting with electroactive species at the electrode/electrolyte interface. In this case, ferrocene was used as the standard species based on the stability of the molecule and the fast, reversible, and kinetically uncomplicated Fc/Fc+ redox changes. Measurements were carried out using Cyclic Voltammetry (CV) with a three-electrode system cell where glassy carbon acted as the working electrode, platinum as the counter electrode, and tungsten oxide wire the pseudo-reference electrode. Based on the resulting voltammogram in the potential range of -0.2 – 0.4 V, it is known that the reaction is quasi-reversible with a potential peak separation (?Ep) of 110 mV. Furthermore, by varying the scan rate (v) from 20 to 300 mV.s-1, it can be seen that the peak current (Ip) produced increases with the given scan rate. Based on the linearity obtained from the Randles-Sevcik equation, it can be seen that the mass transfer process that takes place occurs by diffusion. Furthermore, through the calculation results obtained the value of the diffusion coefficient (D) of ferrocene dissolved in [bmim][PF6] of 3.3 x 10-7 cm2.s-1 and [bmim][TFSI] 1.60 x 10-6 cm2.s-1. The electron transfer rate constant (ks) of the ferrocene complex obtained is 7.9 x 10-4 cm.s-1 in [bmim][PF6] and 1.82 x 10-3 cm.s-1 in [bmim][TFSI]. The presence of mixing of ionic liquid [bmim][TFSI] carried out on [bmim][PF6] overall increases the conductivity, diffusion coefficient and electron transfer rate constant, but is in the range of pure ionic liquid in the order [bmim][PF6] < [bmim][PF6]0,75-[bmim][TFSI]0,25 < [bmim][PF6]0,50-[bmim][TFSI]0,50 < [bmim][PF6]0,25-[bmim][TFSI]0.75 < [bmim][TFSI]. In general, the tendency obtained is influenced by the viscosity of the ionic liquid, which determines the movement characteristics of the ions/molecules. In addition, the interactions formed between the electroactive species and the ionic liquid also affect the kinetics that occurs. Furthermore, through temperature variations, it is known that changes in conductivity values, diffusion coefficients, and electron transfer rate constants are proportional to changes in temperature following the Arrhenius equation. Based on the diffusion activation energy (EaD) and the small decrease in conductivity with temperature, the binary ionic liquid [bmim][PF6]0.50- [bmim][TFSI]0.50 is a superior electrolyte candidate at low-temperature operation