Catalytic electrooxidation of hydrazine at the nickel ferricyanide modified electrode: can an array of surface bound one-electron redox centers act in concert?

The [NiFe(CN)₆]^2-/- derivatized nickel electrode represents an electrocatalytic surface for the mediated oxidation of hydrazine. The four-electron oxidation of hydrazine is employed as a probe of multiple electron charge transfer processes at the Ni[Fe(CN)₆]^2-/- interface since the observed product distribution is sensitive to the detailed mechanism and stoichiometry of electron transfer giving rise to production of NH₃ if only one-electron transfer processes occur, while yielding N₂H₂ or N₂ if multi-electron processes are present. A correlation between surface overlayer structure and charge transfer pathway is observed. A rather facile, pseudo-first order heterogeneous charge transfer rate (~3 × 10^-2 cm s^-1) was found for N₂ production. The kinetics of the processes involved in this electrocatalysis were analyzed according to the Savéant-Andrieux theory. The electrocatalytic behavior of this system can be varied from R type behavior to R + S or (SR) and then to S + E behavior by varying the amount of the surface attached catalyst.