Electrocatalytic Activity of Organically Functionalized Silver Nanoparticles in Oxygen Reduction

Silver nanoparticles capped by a variety of organic ligands (i.e., 1-hexanethiol, 1-octyne, and 4-trifluoromethylphenyl fragments) were synthesized by a chemical reduction route, with the resulting nanoparticles denoted as AgSC6, AgHC8, and AgPhCF3, respectively. The nanoparticle structures were characterized by using a variety of techniques including NMR, UV-vis, infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopies, high-resolution transmission electron microscopy, and electrochemical methods; and their electrocatalytic activities in oxygen reduction in alkaline media were evaluated and compared within the context of metal-ligand interfacial bonding interactions by using “bare” Ag nanoparticles supported on carbon black (Ag/C) as the benchmark materials. The results demonstrated that the electrocatalytic activity increased in the order of AgSC6<Ag/C<AgHC8<AgPhCF3. Of these, the activity of the AgSC6 nanoparticles was even lower than that of Ag/C, whereas the AgPhCF3 nanoparticles exhibited a specific activity that was about 13 times that of Ag/C and an onset potential that was ca. 200 mV more positive than that of Ag/C. The observed discrepancy of the nanoparticle electrocatalytic performance was accounted for by the deliberate manipulation of the nanoparticle electronic energy by the metal-ligand interfacial bonding interactions that dictated the adsorption of oxygen and reaction intermediates and hence the electron-transfer dynamics of oxygen reduction.