Aqueous Redox Transition Metal Complexes for Electrochemical Applications as a Function of pH

Abstract

The electrochemistry of a large number of transition metal complexes of iron, cobalt, chromium, and ruthenium have been examined regarding their anodic and cathode peak potential, peak separation, and reversibility as a function of a broad pH range. Criteria for reversibility are considered. In addition, absorption and/or color characteristics have been described at a fixed pH. The stability of stored samples in terms of cyclic voltammetry and absorption spectra has been examined for a given period of time. A significant number of redox couples have properties which should make them useful in photoelectrochemistry, and other electrochemical applications, catalysis, redox flow cells, and the like.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.171.57.189 Downloaded on 2015-06-13 to IP

Determination of reaction rate between cathodically formed FeII-triethanolamine-complex and FeIII-hepta-d-gluconate complex by cyclic voltammetry

“…2) [1,[8][9][10][11]. The cathodic peak current of the diffusion controlled process (i p ) d is directly proportional to the square root of the scan rate.…”

“…In aqueous alkaline solutions amino compounds and sugar-acids are excellent complexing agents for Fe II -and Fe III -ions [1][2][3]. Iron complexes with sugar acid type ligands are of importance as corrosion inhibitors and in biological systems [4,5].…”

“…Alkali stable iron II/III -complexes are also of interest for the indirect cathodic reduction of vat dyes in different dyeing processes [6,7]. The electrochemical behaviour of the Fe III/II TEA complexes has been studied by different groups (TEA = triethanolamine) [1,[8][9][10]. The reversible cathodic reduction of the Fe(III)-triethanolamine complex is observed at (E p ) c = À1050 mV (vs. Ag/AgCl, 3 M KCl) as reversible redox process [1,8,10].…”

“…The electrochemical behaviour of the Fe III/II TEA complexes has been studied by different groups (TEA = triethanolamine) [1,[8][9][10]. The reversible cathodic reduction of the Fe(III)-triethanolamine complex is observed at (E p ) c = À1050 mV (vs. Ag/AgCl, 3 M KCl) as reversible redox process [1,8,10]. The limited stability of the Fe III/II TEA complexes at lower pH led to the use of mixtures of complexing agents of amino-ligands and sugar acids, e.g., TEA and D-gluconate (DGL) [6].…”

Investigation of electrode material – Redox couple systems for reverse electrodialysis processes. Part I: Iron redox couples

“…For example, in the pH range of 0-14, most of the common chelating agents exist in an equilibrium of both the protonated and unprotonated forms. In addition the complexes may be involved in hydrolysis and/or precipitation [14]. 6.…”