Effect of Surface Charge and Electrode Material on the Size-Dependent Oxidation of Surface-Attached Metal Nanoparticles

摘要

Here we report on the size-dependent oxidation of Au nanoparticles (NPs) electrodeposited directly on indium tin oxide-coated glass (glass/ITO) electrodes as compared to those chemically synthesized and electrostatically or drop-cast deposited onto aminopropyltriethoxysilane (APTES)-modified, mercapto-propyltrimethoxysilane (MPTMS)-modified, or unmodified glass/ITO electrodes. The peak oxidation potential (E_p) of 54 nm diameter Au NPs shifts by as much as 155 mV negative when deposited electrostatically on the highly positively charged glass/ITO/APTES surface and oxidized at low pH as compared to their oxidation on more neutral glass/ITO or glass/ITO/MPTMS surfaces at all pH’s and on glass/ITO/APTES at neutral pH. Electrodeposited Au NPs on glass/ITO of similar size also oxidize at more positive potentials due to the neutral electrode surface charge. Ag NPs show a similar charge dependence on their E_p. Interestingly, the Ep value of Au and Ag NPs smaller than about 10 nm in diameter is independent of surface charge. The E_p of 9 nm diameter citrate-capped Ag NPs attached to Au, Pt, glassy carbon (GC), and glass/ITO electrodes electrostatically through short amine-terminated organic linkers depends on the electrode material, following the order (vs Ag/AgCl) of Au (384 ± 7 mV) ≈ Pt (373 ± 12 mV) > GC (351 ± 2 mV) > glass/ITO (339 ± 1 mV). The underlying electrode material affects the Ag NP E_p even though the NPs are not directly interacting with it. In addition to size, the electrode material and its surface charge have a strong influence on the oxidation potential of surface-confined metallic nanostructures.