Insight into the action mechanism of ammonia in one-pot synthesis of hermetic Al@Ag core–shell particles via deposition model

In this study, Al@Ag particles with hermetic silver shell were successfully prepared by a facile one-pot electroless plating method and the effect of NH3·H2O in reaction process was investigated. The result shows that the concentration ratio of NH3·H2O to Ag+ from 18:1–55:1 triggers a continuous transition of the silver coating from raspberry-like granule to hermetic and then loose. This transition is mainly dependent on the suppression of Ag deposition as increasing NH3·H2O concentration. It was confirmed using silver deposition kinetic and electrochemistry tests. Based on these experimental results, a deposition model was proposed to quantify the specific behavior of NH3·H2O in inhibiting Ag deposition from the perspective of interfacial reaction between active center and [Ag(NH3)2]+. The deposition model was fitted well with experimental results and the effective chemical reaction rate (keff) at solid-liquid interface were calculated, which is the critical factor affecting nucleation and coating quality. As CNH3·H2O:CAg+= 48:1, keff is 0.0117 mol L−1 min−1, a compact core-shell Al@Ag particle is realized and the resistivity as low as 1.21 × 10−4 Ω·cm even with Ag content is 15.61 wt%. This work revealed the dual role of NH3·H2O in complexing Ag+ and regulating keff to control silver grain size and distribution.