Utilizing in Situ Ec-S/TEM to Study Electrochemical Nucleation of Copper from a Bromide Electrolyte
Authors: Stricker Elizabeth A. , Wainright Jesse S. , Savinell Robert F. , Unocic Raymond R 
Published: February 2020

Electrochemical nucleation of metals have long been investigated using chronoamperometry1, cyclic voltammetry2, and electrochemical impedance spectroscopy3
. The current/potential time transients from these methods are used as basis for models for various proposed nucleation mechanisms such as instantaneous and progressive nucleation4. Physical insight has been primarily inferred from the current/potential time transient models and ex situ analysis of the deposit thereafter. However, surface restructuring is known to occur ex situ. In situ methods, such as in situ STM5
and in situ AFM6, minimize ambiguous understanding due to surface restructuring; however, the time resolution of these methods are lacking7. Thus direct correlation between the nucleation processes and electrochemical measurements have not been studied in great detail due to the present lack of in situ characterization methods that permit the simultaneous acquisition of electrochemical measurements with high spatial resolution imaging and high time resolution processing within the electrolyte.

Recent advances in liquid cell in situ electrochemical scanning/transmitting electron microscopy (ec-STEM), mitigates ambiguity due to surface restructuring following nucleation7, 8. In situ ec-STEM can acquire and analyze time-resolved images of the nucleation and growth process at the nanometer-scaled spatial resolution while quantitative electrochemical measurements are concurrently performed. Therefore, this technique can also provide clarity between nucleation growth and classical electrochemical nucleation models such as the Scharifker and Hills4 model and the Sluyter-Rehbach9 model.

Recent advances in an all-copper flow battery has created a renewed interest in copper electrodeposition from a high halide electrolyte10. The high halide electrolyte is unique compared to traditional damascene plating in that the copper (I) oxidation state is stabilized. Here, we apply the in situ ec-STEM approach to investigate the electrochemical nucleation of copper in order to understand the negative electrode reaction in these all-copper batteries. This presentation compares the electrochemical nucleation of copper of high bromide ion electrolyte on a carbon versus copper electrode and discusses the nuances of in situ liquid cell ec-S/TEM.

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