X-ray photoelectron spectroscopic investigation and electrochemistry of polynuclear indium(III) hexacyanoferrate films

Abstract

Abstract An electrochemically deposited indium(III)-hexacyanoferrate (InHCF) film on glassy carbon and platinum electrodes has been investigated by X-ray photoelectron spectroscopy (XPS). Attempts were made to characterise such a polynuclear inorganic film upon its electrochemical conditioning in both reduced and oxidised forms. The indium ions were unaffected by the oxidation state of the film and were present mainly as In(III). In the oxidised form (i.e. conditioned at +0.90 V) the InHCF is unstable during XPS analysis, with Fe being reduced from FeIII to FeII. Profound alterations were also observed in the chemical form of nitrogen. Although the InHCF film was grown in potassium containing solutions, a very low amount of K+ ions was incorporated into the inorganic lattice. This fact, along with the iron to indium ratio of 0.76±0.06 (n=6), is consistent with a potassium-free structure of `insoluble' In4[Fe(CN)6]3 · xH2O. Yet the stability of InHCF films is not very good, and the electrochemical formation of InFe(CN)6 and KInFe(CN)6 is probably the main cause of the film dissolution.