In situ visualization of hierarchical agglomeration growth during electrochemical deposition of Cu nanocrystals in an open ionic liquid cell

Metal nanoparticles have important applications in batteries, fuel cells, electrocatalysis, and sensing. However, their growth mechanisms are still unclear. Here the growth mechanism of Cu nanoparticles during electrochemical deposition was characterized via an in situ transmission electron microscopy observation in an open ionic liquid cell. We revealed a hierarchical agglomeration growth (HAG) mechanism, namely, single Cu atoms were formed first due to electrochemical reduction of Cu2+ ions. The single Cu atoms then agglomerated into nanoclusters, which subsequently recrystallized into small nanocrystals. The small nanocrystals agglomerated into larger nanocrystals, and then formed a porous nanocrystals network with an average grain size of 10 nm. The large Cu nanoparticles are single crystals with numerous multiple twins. A self-limiting grain growth mechanism governed by the Cu2+ ion limited diffusion was also found. Our study demonstrates the possibility of observing nanoparticle growth under realistic electrochemical conditions, which may have important applications in tailoring the nanoparticle size and shape for practical applications. (C) 2022 Elsevier Ltd. All rights reserved.