An FeIII Azamacrocyclic Complex as a pH-Tunable Catholyte and Anolyte for Redox-Flow Battery Applications

Pavel B. Tsitovich; Anjula M. Kosswattaarachchi; Matthew R. Crawley; Timothy Y. Tittiris; Timothy R. Cook; Janet R. Morrow

doi:10.1002/chem.201704381

An Fe^III Azamacrocyclic Complex as a pH-Tunable Catholyte and Anolyte for Redox-Flow Battery Applications

Pavel B. Tsitovich
, Anjula M. Kosswattaarachchi
, Matthew R. Crawley
, Timothy Y. Tittiris
, Timothy R. Cook
, Janet R. Morrow

Research output: Contribution to journal › Article › peer-review

27 Scopus citations

Abstract

A reversible Fe³⁺/Fe²⁺ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The Fe^III complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E_1/2(Fe³⁺/Fe²⁺)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe³⁺/Fe²⁺ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron.

Original language	English (US)
Pages (from-to)	15327-15331
Number of pages	5
Journal	Chemistry - A European Journal
Volume	23
Issue number	61
DOIs	https://doi.org/10.1002/chem.201704381
State	Published - Nov 2 2017
Externally published	Yes

Keywords

azamacrocycles
iron complexes
pH-tunable potential
proton-coupled electron transfer
redox-flow batteries

ASJC Scopus subject areas

Catalysis
Organic Chemistry

Access to Document

10.1002/chem.201704381

Cite this

@article{a3b696cd852f42f79ad98837d57bb5bb,

title = "An FeIII Azamacrocyclic Complex as a pH-Tunable Catholyte and Anolyte for Redox-Flow Battery Applications",

abstract = "A reversible Fe3+/Fe2+ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The FeIII complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron.",

keywords = "azamacrocycles, iron complexes, pH-tunable potential, proton-coupled electron transfer, redox-flow batteries",

author = "Tsitovich, \{Pavel B.\} and Kosswattaarachchi, \{Anjula M.\} and Crawley, \{Matthew R.\} and Tittiris, \{Timothy Y.\} and Cook, \{Timothy R.\} and Morrow, \{Janet R.\}",

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AU - Tsitovich, Pavel B.

AU - Kosswattaarachchi, Anjula M.

AU - Crawley, Matthew R.

AU - Tittiris, Timothy Y.

AU - Cook, Timothy R.

AU - Morrow, Janet R.

PY - 2017/11/2

Y1 - 2017/11/2

N2 - A reversible Fe3+/Fe2+ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The FeIII complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron.

AB - A reversible Fe3+/Fe2+ redox couple of an azamacrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The FeIII complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to −270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 100 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element iron.

KW - azamacrocycles

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KW - pH-tunable potential

KW - proton-coupled electron transfer

KW - redox-flow batteries

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