Comparison of Oxygen Reduction Reaction at Silver Nanoparticles and Polycrystalline Silver Electrodes in Alkaline Solution

Adenosine 5 '-triphosphate capped silver nanoparticles (ATP-Ag NPs) with diameters of 4.5 +/- 1.1 nm were synthesized using a one pot chemical reduction route. After removal of the ATP capping ligands, the electrochemical activity of these NPs for the oxygen reduction reaction (ORR) in aqueous alkaline solution (0.1 M NaOH) was studied in a single layer-by-layer (1 L LbL) film of NPs and compared with bulk polycrystalline Ag using cyclic voltammetry (CV) and rotating disk electrode (RDE) experiments. For the NPs in the 1 L LbL film, the active area of catalyst available for the ORR was calculated using the charge for the underpotential deposition (UPD) of lead (Pb) on the NPs. RDE data were analyzed to determine the ORR rate constant and the number of electrons (n-value) involved in oxygen reduction. Analysis of Koutecky-Levich (K-L) plots indicates an n-value between 3 and 4 with a higher n-value under some conditions for the NPs than for bare polycrystalline Ag. Possible origins of the variation of n-values for the Ag NPs compared to bulk Ag are discussed.