Kinetics of the oxidation of iodide by dicyanobis(phenanthroline)iron(III) in a binary solvent system

Abstract

Oxidation of the iodide ion is an important facet of the solar cells such as perovskite solar cells and dye-sensitized solar cells. The rate of reaction undoubtedly depends upon several factors. Such parameters include reaction media, electrolyte, and the nature of solvents, and electrolyte. If these factors are optimized then the rate of the reaction can be controlled and could be used to get the maximum benefit out of it such as economically and industrially cost-effective uses of the reaction and globally environmentally benign. We studied the kinetics of the oxidation of the iodide ion in the binary solvent system that consisted of 10% (v/v) tertiary butyl alcohol and water. The transition metal complex such as dicyanobis(phenanthroline)iron(III) oxidizes the iodide ion spontaneously without any external triggering with a fast rate at 293 ± 1 K. The reaction was probed under the pseudo-first-order condition with an excess concentration of the iodide ion over dicyanobis(phenanthroline)iron(III) at 0.06 M ionic strength. The reaction was observed independent of the concentration of dicyanobis(phenanthroline)iron(III), that is, the zero order and third order with respect to the iodide ion in the selected solvent system. An overall third-order was observed for the redox reaction. The value of the multiplication product of the molar absorptivity (ɛ), path length of the cuvette (b), and overall rate constant (k) was deduced to be 1.59 × 10 6 M −3 s −1. The observed zero-order rate constant of the reaction was increased by the fractional (1.5) power of the concentration of protons in the excess concentration of acid 1 mM to 0.1 M. The multiplication product of ɛ⋅b to the fractional order rate constant (k′) was found 0.773 M −1.5 s −1 that confirms protonation of triiodide in acidic-10% (v/v) tertiary butyl alcohol-water. The effect of ionic strength showed a similar impact in different compositions of solvents such as 5, 10, and 20% (v/v) tertiary butyl alcoholwater. The observed zero-order rate constant was decreased upon increasing the ionic strength in each medium consisting of the binary solvent system.

Catalytic Effect of 1,4-Dioxane on the Kinetics of the Oxidation of Iodide by Dicyanobis(bipyridine)iron(III) in Water

“…Our results show that in 10% dioxane-water, the reaction rate is double; i.e., it is overall first order as compared to the uncatalyzed reaction where it followed an overall fractional (0.5) order in water medium. The slope of the plot produces an overall first-order rate constant (ɛ•b•k) as 4.438 M −1 s −1 (Figure 7a), according to Equation (36).…”

“…The production of new dyes and electron mediators, as well as a better understanding of their interactions and the interfacial electron transfer kinetics is critical for future advancement in this field and is currently the focus of the DSSCs community's scientific efforts [6][7][8]10,[28][29][30][31][32][33][34][35][36]. In terms of kinetics, efficient cell performance is attained when electron transfer events happen quickly.…”

“…In DSSC, polypyridyl liganded Co(III)/(II) redox couples have been widely used, with a system efficiency of 14% [35,51]. Consequently, the transition metal complexes of Fe(III)/(II) with polypyridyl ligands may have the potential to increase the performance of the DSSC if used as a sensitizer to oxidize iodide [13,36,[52][53][54][55][56][57][58][59][60][61][62][63][64][65].…”

“…The ionic strength was maintained by potassium nitrate (KNO 3 ). The concentration of dicyanobis(bipyridine)iron(III) nitrate was constant at 0.08 mM and that of potassium iodide varied between 0.08 and 4 mM at 293 ± 0.5 K. Linear rate equations of the integration method of various orders as derived and published earlier [36] were implemented on the acquired data to identify the order of reaction with respect to dicyanobis(bipyridine)iron(III). As a result of the most acceptable linear fit R-squared value above other orders, the reaction was observed to undergo the zero order with respect to the concentration of the oxidant; dicyanobis(bipyridine)iron(III) (Equation (1), Figure 1).…”

Catalytic Behavior of Extended π-Conjugation in the Kinetics of Sensitizer-Mediator Interaction

“…The reduction potential of ferrocyanide is comparable to the iodide electrolyte, hence displays its replacement over iodide. The oxidation of iodide by ferricyphen and ferricypyr has been studied in acetonitrile, aqueous tertiary butyl alcohol, and aqueous 1,4-dioxane [23][24][25][26]. The comparative kinetic analysis shows the rapid kinetics of ferricyphen over ferricypyr in binary solvent media under optimized experimental conditions.…”