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 nucleation^{7, 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.

1. Heerman, L.; Tarallo, A. Journal of Electroanalytical Chemistry 1999, 470, (1), 70-76.

2. Williams, D. E.; Wright, G. A. Electrochimica Acta 1976, 21, (11), 1009-1019.

3. Cachet, C.; Saïdani, B.; Wiart, R. Electrochimica Acta 1989, 34, (8), 1249-1250.

4. Scharifker, B.; Hills, G. Electrochimica Acta 1983, 28, (7), 879-889.

5. Itaya, K.; Tomita, E. Surface Science 1988, 201, (3), L507-L512.

6. Rynders, R. M.; Alkire, R. C. Journal of The Electrochemical Society 1994, 141, (5), 1166-1173.

7. Williamson, M. J.; Tromp, R. M.; Vereecken, P. M.; Hull, R.; Ross, F. M. Nat Mater 2003, 2, (8), 532-536.

8. Unocic, R. R.; Sacci, R. L.; Brown, G. M.; Veith, G. M.; Dudney, N. J.; More, K. L.; Walden, F. S., II; Gardiner, D. S.; Damiano, J.; Nackashi, D. P. Microscopy and Microanalysis 2014, 20, (02), 452-461.

9. Sluyters-Rehbach, M.; Wijenberg, J. H. O. J.; Bosco, E.; Sluyters, J. H. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1987, 236, (1–2), 1-20.

10. Lloyd, D.; Magdalena, E.; Sanz, L.; Murtomäki, L.; Kontturi, K. Journal of Power Sources 2015, 292, (0), 87-94.