Site‐Specific Modification of Gold Nanoparticles by Underpotential Deposition of Cadmium Atoms

Underpotential deposition (UPD) of cadmium on 15 nm gold nanoparticles stabilized by 1‐mercapto‐undecane‐11‐tetra(ethylene glycol) has been studied by cyclic voltammetry (CV). Particles are adsorbed to a hanging mercury drop electrode (HMDE). It is shown that single cadmium atoms are deposited onto the same surface sites that are active for adsorptive hydrogen reduction when cadmium is absent. Depending on the solution pH, the deposition of cadmium atoms either blocks hydrogen reduction or vice versa, depending on which process occurs first during the cathodic potential sweep. Another remarkable finding is that single cadmium atoms UPD‐deposited are also active for adsorptive hydrogen reduction. The use of CV to interrogate surface protected nanoparticles adsorbed on a HMDE represents a powerful method to study the electrocatalytic activity. One cathodic step at a time: Poly(ethylene glycol)‐stabilized 15 nm gold nanoparticles possess accessible sites that are highly active for either adsorptive hydrogen ion reduction or underpotential metal‐atom deposition (UPD). As the potential moves in the cathodic direction, three redox processes are verified when particles adsorb on Hg: UPD of cadmium, diffusional Cd deposition on Hg, and finally H+ reduction on Cd0 deposits.