Abstract
A hydrophobic polymer of intrinsic microporosity (PIM-EA-TB) is employed to stabilize an organogel/aqueous electrolyte phase boundary based on an organic water-insoluble 4-(3-phenylpropyl)-pyridine phase. The organogel with electrocatalytic metal complexes embedded is immobilized on glassy carbon or on transparent mesoporous tin-doped indium oxide (ITO) electrodes. Liquid/liquid ion transfer voltammetry is investigated for a 4-(3-phenylpropyl)-pyridine organogel/aqueous electrolyte interface for two types of redox systems: tetraphenylporphyrinato-Mn(III/II) (MnTPP) and phthalocyanato-Mn(III/II) (MnPc). Electron transfer is shown to be coupled to reversible liquid/liquid anion transfer processes for PF6−, ClO4−, SCN−, and NO3−, with a change in mechanism for the more hydrophilic anions Cl−, F−, and SO42−. In situ UV-Vis spectroelectrochemistry reveals reversible Mn(III/II) redox processes coupled to ion transfer for MnTPP. But further complexity and a detrimental side reaction are observed for MnPc causing gradual loss of the electrochemical response in the presence of dioxygen.Graphical ᅟ
Highlights
Liquid/liquid ion transfer processes [1, 2] are fundamentally linked to biological ion transfer across membranes and of considerable interest in analytical procedures and sensing as well as in electrocatalysis, where ion transfer is part of the overall catalytic reaction sequence [3, 4]
The resulting redox process can be described as a combined electron transfer and anion transfer as expressed in Eq 1 [34, 35]
For chloride, fluoride, and sulfate, a mechanism different to that shown in Eq 1 needs to be assumed
Summary
Liquid/liquid ion transfer processes [1, 2] are fundamentally linked to biological ion transfer across membranes and of considerable interest in analytical procedures and sensing as well as in electrocatalysis, where ion transfer is part of the overall catalytic reaction sequence [3, 4]. The possibility to form defined and electrochemically active deposits of PIM-EA-TB–PPP organogels at electrode surfaces is developed here for the case of immobilized tetraphenylporphyrinato-Mn(II) (MnTPP) and phthalocyanato-Mn(II) (MnPc) redox systems (see Fig. 1). Spectroelectrochemistry is employed to follow redox state changes and associated chemical reactions in the organogel Both the redox active molecules (either tetraphenylporphyrinato-Mn(II) or phthalocyanato-Mn(II)) and the water-immiscible organic solvent (4-(3-phenyl-propyl)-pyridine or PPP) are immobilized together with the PIM-EA-TB at glassy carbon (GC) or at porous tin-doped indium oxide (ITO) electrodes. It is shown that coupled electron transfer and anion transfer (see Fig. 1d) occur for a range of aqueous anions (as a function of anion hydrophobicity) and it is demonstrated that the PIM-EA-TB organogel can be used on tin-doped indium oxide (ITO) electrodes to provide stable film deposits for in situ spectroelectrochemical measurements. Standard quartz cuvettes were fitted with electrodes (see below)
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