Single Particle Electrochemical Oxidation of Polyvinylpyrrolidone-Capped Silver Nanospheres, Nanocubes, and Nanoplates in Potassium Nitrate and Potassium Hydroxide Solutions

Single particle electrochemical oxidation of poly(vinylpyrrolidone)-capped silver nanoparticles at a microdisk electrode was investigated as a function of particle shape (spheres, cubes, and plates) in potassium nitrate and potassium hydroxide solutions. In potassium nitrate, extreme anodic potentials (≥1500 mV vs. Ag/AgCl (3 M KCl)) were necessary to achieve oxidation, while lower anodic potentials were required in potassium hydroxide (≥900 mV vs. Ag/AgCl (saturated KCl)). Upon oxidation, silver oxide is formed, readily catalyzing water oxidation, producing a spike-step current response. The spike duration for each particle was used to probe effects of particle shape on the oxidation mechanism, and is substantially shorter in nitrate at the large overpotentials than in hydroxide solution. The integration of current spikes indicate initial oxidation to Ag(I) in a mixed-valance complex. In both electrolytes, the rate of silver oxidation strongly depends on silver content of the nanoparticles, rather than the shape-dependent variable–surface area. The step height, which reflects rate of water oxidation, also tracks the silver content more so than shape. Results were compared to those from less-protected citrate-capped particles and suggest that contributions of the polymer capping ligand to kinetic barriers to oxidation are negligible under these conditions.