Abstract
Kinetic analysis of the electrocatalytic reduction of H2O2 on electrodes modified with thin Prussian blue films was performed and a full set of kinetic parameters governing the rate of the electrocatalytic reaction was determined. Rate constant (κ·k') for the catalytic reaction between H2O2 and the reduced form of Prussian blue incorporating interstitial Cs+ and K+ ions was calculated to be equal to 3.1·106 and 2.3·106 cm3·mol–1 s–1, respectively. The diffusion coefficient of H2O2 and the apparent diffusion coefficient of electrons in the reduced form of Prussian blue were found to be κ·DS(H2O2) = 2.6·10–7 cm2/s and De = 2.8·10–12 cm2/s, respectively.
Highlights
S INCE the first report on the electrocatalytic reduction of hydrogen peroxide on electrodes modified with thin redox-active films of Prussian blue (PB) by Itaya in 1984,[1] PB has been considered as one of the best non-platinum group metal catalysts for electrochemical reduction of H2O2, especially for the applications in electrochemical hydrogen peroxide sensors and biosensors based on oxidase enzymes.[2,3,4,5]
PB is iron(III) hexacyanoferrate(II), a polymeric, non-stoichiometric mixed-valence compound, which composition can vary between two limiting stoichiometries, the so-called "insoluble PB", Fe(III)4[Fe(II)(CN)6]3, and "soluble# PB", MFe(III)[Fe(II)(CN)6], differing in the amount of [Fe(II)(CN)6]4– vacancies situated at the Fe2+ lattice sites and the number of monovalent cations M+ occupying the interstitial sites of the cubic crystal lattice of PB.[6,7,8],§ Electrocatalytic activity of PB towards hydrogen peroxide reduction relies on the ability of Fe3+ ions in PB to be reversibly reduced to the +2 oxidation state [Eq (1)], giving the reduced form of PB, iron(II) hexacyanoferrate(II), the so-called Prussian white (PW)
H2O2 on PB are relatively scarce and limited to evaluation of the rate constant of heterogeneous catalytic reaction between PB and H2O2.[1,16,17,18] Since the rate of the overall electrocatalytic process occurring within the volume of a thin, three-dimensional electrocatalytic film depends on the rate of the heterogeneous catalytic reaction and on the rates of substrate diffusion and charge propagation through the electrocatalytic film,[19,20] the lack of reliable kinetic parameters that determine the electrocatalytic performances of PB significantly reduces the possibilities for rational design of PB-modified electrodes
Summary
S INCE the first report on the electrocatalytic reduction of hydrogen peroxide on electrodes modified with thin redox-active films of Prussian blue (PB) by Itaya in 1984,[1] PB has been considered as one of the best non-platinum group metal catalysts for electrochemical reduction of H2O2, especially for the applications in electrochemical hydrogen peroxide sensors and biosensors based on oxidase enzymes.[2,3,4,5] Chemically, PB is iron(III) hexacyanoferrate(II), a polymeric, non-stoichiometric mixed-valence compound, which composition can vary between two limiting stoichiometries, the so-called "insoluble PB", Fe(III)4[Fe(II)(CN)6]3, and "soluble# PB", MFe(III)[Fe(II)(CN)6], differing in the amount of [Fe(II)(CN)6]4– vacancies situated at the Fe2+ lattice sites and the number of monovalent cations M+ (typically alkali metal cations or NH4+) occupying the interstitial sites of the cubic crystal lattice of PB.[6,7,8],§ Electrocatalytic activity of PB towards hydrogen peroxide reduction relies on the ability of Fe3+ ions in PB to be reversibly reduced to the +2 oxidation state [Eq (1)], giving the reduced form of PB, iron(II) hexacyanoferrate(II), the so-called Prussian white (PW).
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