Remarks on the Electrochemical Potential of Small Silver Clusters in Aqueous Solution

Silver clusters in aqueous solutions containing excess Ag + ions may be regarded as tiny metal‐electrodes. The electrochemical standard potentials of metal electrode equilibria Ag n ⇆Ag n ‐1 + Ag + + e − are much more negative than that of the compact silver‐metal electrode. The potential generally strives toward the value of the compact electrode with increasing agglomeration n of the particles, although a strong oscillation occurs in the n = 1 to 3 range. The trend is opposite to the size dependence of the ionization potential in vacuo. The main factor determining the redox potential in solution is not the hydration of the clusters {as one may suppose at first sight} but the binding energy of a silver atom in a cluster. — The electrochemical potentials of equilibria of the type Ag n ⇆Ag n + e − and Ag n − ⇆Ag n + e − are also discussed. — It is pointed out that results from photoionization experiments on clusters in vacuo would importantly improve our present knowledge of the electrochemistry of clusters.