Osmium hexacyanoferrate films have been prepared using repeated cyclic voltammetry, and the deposition process and the films' electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of osmium hexacyanoferrate films directly from the mixing of Os3+ and Fe(CN)(6)(3-) ions from solutions containing various cations. An electrochemical quartz crystal microbalance, cyclic voltarnmetry, and UV-visible spectroscopy were used to study the growth mechanism of the osmium hexacyanoferrate films. The osmium hexacyanofeffate films showed a single redox couple, and the redox reactions included "electron transfer" and "proton transfer" with a formal potential that demonstrates a proton effect in acidic solutions up to a 12 M aqueous HCI solution. The electrochemical and electrochemical quartz crystal microbalance results indicate that the redox process was confined to the immobilized osmium hexacyanoferrate film. The electrocatalytic reduction of dopamine, epinephrine, norepinephrine, S2O32-, and SO52-by the osmium hexacyanoferrate films was performed. The preparation and electrochemical properties of co-deposited osmium(III) hexacyanoferrate and copper(H) hexacyanoferrate films were determined, and their two redox couples showed formal potentials that demonstrated a proton effect and an alkaline cation effect, respectively. Electrocatalytic reactions on the hybrid films were also investigated. (C) 2004 Elsevier Ltd. All rights reserved.