Electrochemistry of ferric ruthenocyanide (Ruthenium Purple), and its electrocatalysis for proton reduction

Electrochemistry of ferric ruthenocyanide (Ruthenium Purple, RP) was studie d in acidic solutions containing a sodium salt (NaH2PO4 or NaCl). Two kinds of redox peaks for the Fe-III,Fe-II couple were clearly seen in a Na+ solu tion, originating from a composite structure of both Fe-4(III)[Ru-II(CN)(6) ](3) (insoluble) and Fe-III[Ru-II(CN)(6)](-) (soluble). In repeated CV scan s in a NaCl solution, it was found that only the couple of the redox peak a ssigned to the insoluble form remains unchanged under the steady state. The ratio of the insoluble form was estimated by coulometry as ca. 40% of the initial coated unit cells of the RP. Efficient electrocatalytic H-2 formati on was found to take place with the aid of the RP although this electrocata lysis was dependent on the type of sodium salt employed. In order to invest igate the dominant factor affecting the overall kinetics in the H+ reductio n catalysis, the dependences of both the catalytic activity and the electro n transfer rate in the RP film were studied in a NaH2PO4 solution as a func tion of the coated amount. It was found that the overall kinetics are not d ominated by electron transfer in the RP film. (C) 2001 Elsevier Science B.V . All rights reserved.