Electroactivation of Microparticles of Silver on Glassy Carbon for Oxygen Reduction and Oxidation Reactions

The electrocatalytic properties of small amounts of silver (3–17 μg cm−2) electrodeposited on glassy carbon can be sensibly increased by an activation protocol based on pretreatment oxidation/reduction cycles that produces significant changes in particle’s morphology. The catalytic effects on both Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR) are evaluated by the onset potentials of the voltammetric curves, and the number of electrons involved in ORR is evaluated by the Levich plot. Tafel plots of both OER and ORR curves obtained after the activation protocol show significant changes that rule out the hypothesis that the catalytic effect could only be attributed to an increased roughness of the samples. Furthermore, the electrochemically active surface area of silver, as measured by the charge involved in Pb underpotential deposition, was found to increase linearly with the amount of depositing silver. On the contrary, the Tafel plots of increasing amounts of silver show that the increase of the catalytic effect with silver loading is not linear as expected in a mere increase of the roughness factor. Levich-Koutecky and Tafel plots evidenced that the highest silver loading showed a catalytic effect greater than that expected on the basis of the electrochemically active surface area.