Electrocatalytic reduction of hydrogen peroxide at Prussian blue modified electrodes: a RDE study

Electrocatalytic reduction of hydrogen peroxide at Prussian blue modified electrode has been studied with rotating disk electrode in pH 5.5 and 7.3 solutions. It has been shown that the electrocatalytic cathodic reduction obeys Koutecky-Levich relationship at electrode potentials ranging from 0.1 to -0.4 V vs. Ag/AgCl for low concentrations of peroxide not exceeding 0.3 mM. Within this potential window, the calculated kinetic cathodic current ranges within the limits of 2.15-6.09 and 1.00-3.60 mA cm(-2) mM(-1) for pH 5.5 and 7.3, respectively. For pH 5.5 and 7.3 solutions, a linear slope of the dependence of kinetic current on electrode potential of -10.8 and -2.89 mA cm(-2) mM(-1) V-1, respectively, has been obtained. At a higher concentration of peroxide, exceeding 0.6 mM, deviations from Koutecky-Levich relationship have been observed. These deviations appear more expressed at higher potentials and higher solution pH. The results obtained have been interpreted within the frame of two-step reaction mechanism, including (1) dissociative adsorption of hydrogen peroxide with the formation of OH radicals and (2) one-electron reduction of these radicals to OH- anions. At a higher concentration of peroxide, and especially at a higher pH, the second process becomes rate limiting.