Analysis by X-ray photoelectron spectroscopy of ruthenium stabilised polynuclear hexacyanometallate film electrodes Original Research Article

The role and effects of ruthenium on the electrochemical stabilisation of some metal-hexacyanometallate film electrodes was investigated by X-ray photoelectron spectroscopy (XPS). The following inorganic films were studied, cobalt(II)-hexacyanoferrate(II/III) (CoHCFe), nickel(II)-hexacyanoferrate(II/III) (NiHCFe), and iron(II/III)-hexacyanorutenate(II/III) (FeHCRu), and their corresponding ruthenium stabilised ones, Ru-CoHCFe, Ru-NiHCFe and Ru-FeHCRu. A mass increase of CoHCFe, NiHCFe, and FeHCRu, during continuous redox cycles (75–90 times) in a millimolar solution of RuCl3, was monitored by an electrochemical quartz crystal microbalance. Detailed XPS analysis of C 1s, O 1s, Fe 2p, Ni 2p, Co 2p, and Ru 3d peaks has allowed a comprehensive description of changes that occurred. The results obtained demonstrate that the insertion of ruthenium oxo species (e.g., Ru2O63+) was effective for the increase in lifetimes and for the electrocatalytic properties of ruthenium-modified metal-hexacyanometallate film electrodes. Three possible models of stabilisation are discussed.