Electrochemical analysis of the kinetics and mechanism of the oxygen reduction reaction on Au nanoparticles

Au nanoparticles have been chemically synthesized and supported in carbon Vulcan XC-72. Using the Au nanoparticles as catalyst, the kinetics and mechanism of the oxygen reduction reaction (ORR), in 0.5 M H2SO4, were analyzed. From rotating disk electrode (RDE) studies, it was found that the number of electrons (n) involved in the ORR depends on the applied potential (E). For E similar to 0.38 V. n was similar to 2, at more negative potentials the value of n increases almost to 4. The kinetic parameters obtained from RDE studies were: -b= 0.110 V dec(-1) and alpha = 0.54. The impedance spectra of Au nanoparticles show one time constant for E> 0.38 V vs. NHE, the time constant was associated to the reduction process from O-2 to H2O2 as the main intermediate. For E < 0.38 V vs. NHE a second time constant appears, and it was associated to the reduction of H2O2 to H2O. The values of charge transfer resistance (R-ct1) obtained from the impedance spectra allows determining the kinetic parameters of the ORR on Au, the Tafel slope (-b= 0.111 V dec(-1)) and charge transfer coefficient (alpha = 0.53) were calculated. The kinetic values b and alpha obtained from ROE and EIS measurements are in good agreement with each other. (C) 2010 Elsevier B.V. All rights reserved.