Iridium-Based Hexacyanometallate Thin Films in Aqueous Electrolytes

Abstract

Thin films of metal-hexacyanoiridium(III) (MHCI), KxMy[Ir(CN)6]z, where M = Ru, Fe were electrochemically prepared and used as surface modifiers for glassy carbon electrodes. The redox behaviour of the counter/central ions of these films was investigated in aqueous electrolytes using cyclic voltammetry, chronocoulometry and electrochemical impedance spectroscopy. An electrochemical synthesis of zeolite-like films of KxMy[Ir(CN)6]z and KxFey[Fe(CN)6]z (Prussian blue) was also undertaken using the cyclic voltammetric technique. Porous multifilm assemblies of Prussian blue and MHCI were formed either by the direct electrodeposition of Prussian blue over MHCI or Prussian blue over MHCI during repetitive potential cycling, or by electrochemically-driven insertion-substitution methods. In acidic aqueous KCl, iron hexacyano iridate (FeHCI) displays two redox waves with formal potential E o f ≈ 0.35 and 0.6 V vs. Ag/AgCl. The electrochemical behaviour of FeHCI was compared with that of related hexacyanometallate compounds, such as KRux[Ru(CN)6]y, KRux[Fe(CN)6]y and KFex[Fe(CN)6]y. In addition, evidence for the catalytic behaviour of MHCI films towards the reduction of iodate, IO3 – , is reported.