Synergistic Effect and Mechanism of Reducing and Complexing Agents for the Preparation of Silver-Coated Copper Powders

Silver-coated copper (Cu@Ag) powders prepared by electroless deposition possess wide applications due to high conductivity and good stability. However, the synergistic mechanism between reducing and complexing agent is unclear, and the preparation of uniform Cu@Ag powders is still a challenge. Here, the synergistic effect and mechanism of reducing and complexing agents for the preparation of Cu@Ag powders were studied. It was confirmed that formaldehyde with aldehyde group exhibited stronger reducing ability than glucose. The synergistic effect between reducing agents (i.e. formaldehyde and glucose) and complexing agents (i.e. potassium sodium tartrate, citric acid and ethylenediaminetetraacetic acid) on homogeneous preparation of Cu@Ag powders was elucidated. It was found that formaldehyde and potassium sodium tartrate were the optimum matching reducing agent and complexing agent. Cu@Ag powders with good core–shell structure were obtained and the resistivity was only 0.112 mΩ·cm. It is ascribed to moderate dissociation energy difference between copper and silver complexing ions. Cu@Ag powders obtained under optimum conditions possessed good oxidation resistance. Compared to copper powders, the weight gain of Cu@Ag powder decreased from 25.5% to 19.3% at 519.5 °C. This work provides a theoretical basis to select and match reducing and complexing agents for the preparation of uniform Cu@Ag powders.