Potential and temperature dependence of hydrogen peroxide oxidation at nickel electrodes

The electrochemical oxidation of H2O2 at a nickel rotating disc electrode w as studied in 100 mM phosphate buffer at pH 7.26 over the temperature range 5-35 degreesC, [H2O2] range 0 to 130 mM, rotation rates 630 to 10 000 rpm and anodic potential +364 to +1068 mV vs. Ag/AgCl using staircase voltammet ry. These results were compared with those previously reported for platinum electrodes (S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim, Acta., 1998, 43, 579; ibid., 1998, 43, 2015; ibid., 1999, 44, 2455; ibid., 1999, 44, 4573; ibid., 2000, 45, 3573). The rate of oxidation of H2O2 on nickel i s 15-20 times slower than on platinum. Modifications were made to the bindi ng-site mechanism established for the reaction at platinum (S. B. Hall, E. A. Khudaish and A. L. Hart, Electrochim. Acta, 1999, 44, 2455) to account f or the kinetics at nickel. These included removing the consideration of pro ton inhibition and constraining the rate of regeneration of the binding sit e to potential-invariance. Thermodynamic and kinetic parameters together wi th the pseudo-activation energy for the formation of the reduced binding si te were evaluated.