Quantitative determination of chemical species in high concentration ZnX2 (X = Br and I) media by steady state voltammetry on Pt ultramicroelectrode

Jihye Lee, Jiseon Hwang, Jinho Chang

Research output: Contribution to journalArticleResearchpeer-review

1 Citation (Scopus)

Abstract

In this article, we present the voltammetric approach to quantitatively determine zinc-halides (Zn-X, X = Br and I) complexes in the high concentration ZnX2 solutions by the measurements of the steady state current, iss associated with electrochemical oxidation of X on Pt ultramicroelectrode (UME). At first, iss from electro-oxidation of uncoordinated I as a function of total concentration of I, CI, total in the ZnI2 solutions were deviated from the theoretical iss under the pure diffusion-controlled condition, iss,diffusion to the lower values, respectively. The deviation from iss,diffusion to the lower iss in the ZnI2 solutions cannot be explained by migration but is associated with Zn-I complexation. From the Raman spectra, both ZnI3 and ZnI4 2 − exist at CZnI2 > 0.25 M. Since only free I can be electrochemically oxidized, CI, free is decreased as CZnI2 becomes higher due to the consumption of free I to form ZnI3 and ZnI4 2 −. Therefore, CI, free can be determined by the stability constants of ZnI3 and ZnI4 2 −, β3, Zn − I and β4, Zn − I , which were estimated by the finite element analysis under the migration model. From β3, Zn − I and β4, Zn − I, the accurate concentration of chemical species (I, Zn2 +, ZnI3 , and ZnI4 2 −) were able to be quantitatively determined. β2, Zn − Br, β3, Zn − Br, and β4, Zn − Br in the ZnBr2 solutions were also estimated by the same analytical approach, and the concentration of the chemical species (Br, Zn+, ZnBr3 , and ZnBr4 2 −) were plotted as a function of CBr, total. The concentration of the chemical species in the ZnX2 solutions are further predicted as CX, total becomes 14 M, and the lowest limit of energy density in the suggested ZnX2 redox flow batteries (RFBs) is also discussed based on the estimated CX, free as a function of CX, total.

Original languageEnglish
Pages (from-to)141-149
Number of pages9
JournalJournal of Electroanalytical Chemistry
Volume808
DOIs
StatePublished - 2018 Jan 1

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Voltammetry
Electrooxidation
Electrochemical oxidation
Complexation
Raman scattering
Zinc
Finite element method

Keywords

  • Chemical speciation
  • Finite element analysis
  • Migration
  • Redox flow battery
  • Ultramicroelectrode
  • Zn-polyiodide

Cite this

@article{7d965398e2234012b8df279b253a3689,
title = "Quantitative determination of chemical species in high concentration ZnX2 (X = Br and I) media by steady state voltammetry on Pt ultramicroelectrode",
abstract = "In this article, we present the voltammetric approach to quantitatively determine zinc-halides (Zn-X−, X = Br and I) complexes in the high concentration ZnX2 solutions by the measurements of the steady state current, iss associated with electrochemical oxidation of X− on Pt ultramicroelectrode (UME). At first, iss from electro-oxidation of uncoordinated I− as a function of total concentration of I−, CI−, total in the ZnI2 solutions were deviated from the theoretical iss under the pure diffusion-controlled condition, iss,diffusion to the lower values, respectively. The deviation from iss,diffusion to the lower iss in the ZnI2 solutions cannot be explained by migration but is associated with Zn-I− complexation. From the Raman spectra, both ZnI3 − and ZnI4 2 − exist at CZnI2 > 0.25 M. Since only free I− can be electrochemically oxidized, CI−, free is decreased as CZnI2 becomes higher due to the consumption of free I− to form ZnI3 − and ZnI4 2 −. Therefore, CI−, free can be determined by the stability constants of ZnI3 − and ZnI4 2 −, β3, Zn − I− and β4, Zn − I− , which were estimated by the finite element analysis under the migration model. From β3, Zn − I and β4, Zn − I, the accurate concentration of chemical species (I−, Zn2 +, ZnI3 −, and ZnI4 2 −) were able to be quantitatively determined. β2, Zn − Br, β3, Zn − Br, and β4, Zn − Br in the ZnBr2 solutions were also estimated by the same analytical approach, and the concentration of the chemical species (Br−, Zn+, ZnBr3 −, and ZnBr4 2 −) were plotted as a function of CBr−, total. The concentration of the chemical species in the ZnX2 solutions are further predicted as CX−, total becomes 14 M, and the lowest limit of energy density in the suggested ZnX2 redox flow batteries (RFBs) is also discussed based on the estimated CX−, free as a function of CX−, total.",
keywords = "Chemical speciation, Finite element analysis, Migration, Redox flow battery, Ultramicroelectrode, Zn-polyiodide",
author = "Jihye Lee and Jiseon Hwang and Jinho Chang",
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Quantitative determination of chemical species in high concentration ZnX2 (X = Br and I) media by steady state voltammetry on Pt ultramicroelectrode. / Lee, Jihye; Hwang, Jiseon; Chang, Jinho.

In: Journal of Electroanalytical Chemistry, Vol. 808, 01.01.2018, p. 141-149.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Quantitative determination of chemical species in high concentration ZnX2 (X = Br and I) media by steady state voltammetry on Pt ultramicroelectrode

AU - Lee, Jihye

AU - Hwang, Jiseon

AU - Chang, Jinho

PY - 2018/1/1

Y1 - 2018/1/1

N2 - In this article, we present the voltammetric approach to quantitatively determine zinc-halides (Zn-X−, X = Br and I) complexes in the high concentration ZnX2 solutions by the measurements of the steady state current, iss associated with electrochemical oxidation of X− on Pt ultramicroelectrode (UME). At first, iss from electro-oxidation of uncoordinated I− as a function of total concentration of I−, CI−, total in the ZnI2 solutions were deviated from the theoretical iss under the pure diffusion-controlled condition, iss,diffusion to the lower values, respectively. The deviation from iss,diffusion to the lower iss in the ZnI2 solutions cannot be explained by migration but is associated with Zn-I− complexation. From the Raman spectra, both ZnI3 − and ZnI4 2 − exist at CZnI2 > 0.25 M. Since only free I− can be electrochemically oxidized, CI−, free is decreased as CZnI2 becomes higher due to the consumption of free I− to form ZnI3 − and ZnI4 2 −. Therefore, CI−, free can be determined by the stability constants of ZnI3 − and ZnI4 2 −, β3, Zn − I− and β4, Zn − I− , which were estimated by the finite element analysis under the migration model. From β3, Zn − I and β4, Zn − I, the accurate concentration of chemical species (I−, Zn2 +, ZnI3 −, and ZnI4 2 −) were able to be quantitatively determined. β2, Zn − Br, β3, Zn − Br, and β4, Zn − Br in the ZnBr2 solutions were also estimated by the same analytical approach, and the concentration of the chemical species (Br−, Zn+, ZnBr3 −, and ZnBr4 2 −) were plotted as a function of CBr−, total. The concentration of the chemical species in the ZnX2 solutions are further predicted as CX−, total becomes 14 M, and the lowest limit of energy density in the suggested ZnX2 redox flow batteries (RFBs) is also discussed based on the estimated CX−, free as a function of CX−, total.

AB - In this article, we present the voltammetric approach to quantitatively determine zinc-halides (Zn-X−, X = Br and I) complexes in the high concentration ZnX2 solutions by the measurements of the steady state current, iss associated with electrochemical oxidation of X− on Pt ultramicroelectrode (UME). At first, iss from electro-oxidation of uncoordinated I− as a function of total concentration of I−, CI−, total in the ZnI2 solutions were deviated from the theoretical iss under the pure diffusion-controlled condition, iss,diffusion to the lower values, respectively. The deviation from iss,diffusion to the lower iss in the ZnI2 solutions cannot be explained by migration but is associated with Zn-I− complexation. From the Raman spectra, both ZnI3 − and ZnI4 2 − exist at CZnI2 > 0.25 M. Since only free I− can be electrochemically oxidized, CI−, free is decreased as CZnI2 becomes higher due to the consumption of free I− to form ZnI3 − and ZnI4 2 −. Therefore, CI−, free can be determined by the stability constants of ZnI3 − and ZnI4 2 −, β3, Zn − I− and β4, Zn − I− , which were estimated by the finite element analysis under the migration model. From β3, Zn − I and β4, Zn − I, the accurate concentration of chemical species (I−, Zn2 +, ZnI3 −, and ZnI4 2 −) were able to be quantitatively determined. β2, Zn − Br, β3, Zn − Br, and β4, Zn − Br in the ZnBr2 solutions were also estimated by the same analytical approach, and the concentration of the chemical species (Br−, Zn+, ZnBr3 −, and ZnBr4 2 −) were plotted as a function of CBr−, total. The concentration of the chemical species in the ZnX2 solutions are further predicted as CX−, total becomes 14 M, and the lowest limit of energy density in the suggested ZnX2 redox flow batteries (RFBs) is also discussed based on the estimated CX−, free as a function of CX−, total.

KW - Chemical speciation

KW - Finite element analysis

KW - Migration

KW - Redox flow battery

KW - Ultramicroelectrode

KW - Zn-polyiodide

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U2 - 10.1016/j.jelechem.2017.11.075

DO - 10.1016/j.jelechem.2017.11.075

M3 - Article

VL - 808

SP - 141

EP - 149

JO - Journal of Electroanalytical Chemistry

JF - Journal of Electroanalytical Chemistry

SN - 1572-6657

ER -