Determination of the kinetic parameters of oxygen reduction on copper using a rotating ring single crystal disk assembly (RRDCu(h k l)E)

The kinetics of the oxygen reduction reaction (orr) on Cu(hkl) surfaces are investigated in perchloric acid and sulfuric acid solutions using rotating ring disk electrode (RRDCu(hkl)E). Parameters, such as reaction order, kinetic current, rate constant, Tafel slopes as well as the number of electrons transferred are determined. The variation in the activity and reaction pathway with the crystal faces in different electrolytes is related to the surface characteristics of Cu(hkl) and the structure-sensitive inhibiting effect of the adsorbed anions on their surfaces. In 0.1 M HCiO(4), the difference in activity is clearly observed on Cu(hkl) surfaces (Cu(100) > Cu(111) although it is relatively small). The higher activity of Cu(100) arises from its more open characteristics which may facilitate the co-adsorption of O-2. On the other hand, the adsorption of oxygenated species on Cu(111) at E > -0.35 V induces a 2 e(-) pathway; while a 4 e(-) reduction is observed on Cu(100) in the entire potential region (-0.70 V < E < -0.10 V). In 0.5 M H2SO4, the sequence in activity between Cu(111) and Cu(100) varies with the potentials, i.e., Cu(100) is initially more active than Cu(111) at -0.35 V < E < -0.15 V, however, the reversal in the activity between Cu(111) and Cu(100) is observed at more negative potentials (-0.45 V < E < -0.35 V). The desorption of strongly adsorbed (bi)sulfate anions on Cu(111) induces the 2 e(-) reduction via peroxide formation, however, a 4 e- reduction is dominant on the Cu(100) surfaces. The major effect of (bi)sulfate anions and oxygenated species on the orr kinetics and reaction pathway on Cu(hkl) surfaces is the blocking of active copper sites for the adsorption of O-2 molecules. (c) 2007 Elsevier Ltd. All rights reserved.