Influence of citric acid on the silver electrodeposition from aqueous AgNO3 solutions

The electrodeposition of silver at 25 °C from aqueous AgNO3+ citric acid solutions was investigated. This study shows that it is possible to obtain compact, homogeneous and coherent deposits from aqueous AgNO3 solutions containing citric acid (H3Ci). The morphology as well as the roughness of the deposits was independent of the solution composition. On the contrary, deposits obtained from citrate-free solutions were neither homogeneous nor compact. All deposits exhibited a pronounced preferred orientation with a 〈2 1 1〉-texture axis. The XRD diagrams of all deposits presented an additional reflection, which cannot be indexed in terms of an fcc structure. This extra reflection was attributed to the double Bragg reflection from crystallites in twin position. The relevant chemical entity controlling growth inhibition is a neutral associate Ag2HCi formed in the solution between Ag+ and citrate divalent anions HCi2−. Most of the structural features of silver deposits, such as degree of preferred orientation Q2 1 1 or intensity of the observed extra reflection, depend on the concentration of this associate. Consequently, the structural characteristics of deposits can easily be modified by: (a) changing the concentration of AgNO3 and H3Ci and (b) adjusting the pH of the bulk solution by adding HNO3.