Immobilisation of Iron Porphyrin from an Equilibrium Solution with Diazonium‐Functionalised Axial Ligand: Dependence of Film Composition on Grafting Potential

Abstract

In dichloromethane solution, tetraphenylporphyrin iron (III) chloride (FeTPPCl) and 4‐(1H‐Imidazol‐1‐yl)aniline (Im‐Ph‐NH2) exist in equilibrium with axially‐coordinated [FeTPP(Im‐Ph‐NH2)n]+ (n=1 and 2). After in situ diazotisation of Im‐Ph‐NH2, electroreduction of the diazonium ion leads to deposition of a film incorporating [FeTPP(Im‐Ph)2]+ and uncoordinated Im‐Ph. In the 1 : 1 FeTPPCl:Im‐Ph‐NH2 grafting solution used in this work, Im‐Ph‐NH2 is mostly uncoordinated. However, the formation constant for axially coordinated Fe(II)TPP is significantly greater than for Fe(III)TPP+. Consequently, the relative amounts of coordinated and uncoordinated Im‐Ph in the films depends on whether the grafting scans traverse the potential for reduction of FeTPPCl. In addition, redox grafting can occur based on the Fe(III)/(II) couple of solution‐ and film‐based porphyrin. Electrochemistry, atomic force microscopy and X‐ray photoelectron spectroscopy reveal that the relative amount of free and coordinated Im‐Ph, and concentration of [FeTPP(Im‐Ph)2]+ in the films depend on the negative potential limit during grafting.

Visualizing Water Reduction with Diazonium Grafting on a Glassy Carbon Electrode Surface in a Water-in-Salt Electrolyte

“…The above physical characterization results show that a hydrophobic polymer layer was successfully generated on the electrode surface by applying the diazo-grafted formulation, i.e., the GraftFast process. Many recent works − ,− already showed similar XPS results for successful grafting on GC. For example, Thomas et al achieved hydrophobic gas diffusion layers by diazonium grafting CF 3 -terminated amines on GC, and the XPS study demonstrated the successful grafting process.…”

“…XPS analysis further identified the hydrophobic coatings based on PEG or AGC, consistent with other reported work. Cyclic voltammetry (CV) of the redox probe again reflected the presence of hydrophobic layers that had already been established. − As a result, in the 20 m LiTFSI electrolyte, the result showed that the free water reduction process is not observed with grafted GC electrodes by the LSV measurement, compared with a prominent free water reduction peak on a bare GC. Also, it excites a more negatively bound water reduction peak after grafting hydrophobic layers.…”