A Novel View on the Electrochemical Nucleation and Growth of Metals and Alloys By Local Electrochemistry and Correlative Electron Microscopy
Authors: Ustarroz Jon , Torres Daniel , Parpal Gimenez Monica , Mourtada Souheil , El Marini Mohamed , Bertolucci Coelho Leonardo 
Published: December 2024

Electrochemical deposition offers the opportunity for precise control, scalability, cost-effectiveness, and environmental friendliness, making it the preferred method for synthesizing (nano)materials for various applications [1]. Yet, this requires a comprehensive understanding of the formation of a new solid phase on a foreign substrate, particularly in its early stages. The formation of nuclei on a substrate are critical steps determining the physicochemical properties of the deposit, which are inherently influenced by the surface properties of the substrate. The in-depth experimental assessment of the process is very challenging due to the random nature of initiation events (nucleation), the heterogeneity of surfaces and the (very) fast kinetics across several length scales. For all that, our understanding of the mechanisms involved is inaccurate and incomplete [2].
This process is commonly examined by electrochemical characterization, coupled with ex-situ (post-mortem) evaluation of the deposits. When coupling this standard approach with TEM compatible substrates, it has brought valuable evidence of non-classical growth pathways, which need to be fully understood to fine-tune size, shape and composition of nanostructured materials [3,4]. Yet, it does not capture the influence of the heterogeneous nature of the surface where EN&G proceeds, nor the dynamics before, during and after nucleation [5].
Over the past years, our group has been tackling these challenges by combining (high-throughput) local electrochemistry by Scanning Electrochemical Cell Microscopy (SECCM), with ex-situ and in-situ electron microscopy and data-centric analyses to study the electrochemical nucleation and growth of metals, and more recently alloys, on carbon surfaces [6-8]. This correlative microscopy approach enables unambiguous correlations and clears the path towards a better understanding of the electrochemical response at the local scale.
In this contribution, we show how both overpotential and surface state significantly influence the probability of nucleation. Experiments with varying probe sizes demonstrate that the nucleation rate distribution is also influenced by the electrode's area. Our derived analytical model successfully fits experimental current transients, revealing an excellent correlation between the number of active sites inferred from the model and the number of nanoparticles observed by FESEM. [9] Systematic understanding of correlations among nucleation, growth and structure of deposits, and the accurate depiction of the current transients, are the cornerstones of precise electrochemical manufacturing of micro- and nanostructures.
Furthermore, our integrated scanning microscopy approach offers a robust framework for generating rich experimental data, laying the foundation for future investigations. These are the bridge connecting the microscopic world to macroscopic outcomes, shedding light on how surface heterogeneities influence nucleation rates and electrodeposit properties.
References:
[1] Bernal, M. et al. Current Opinion in Electrochemistry 27, 100688 (2021).
[2] Ustarroz, J. Current Opinion in Electrochemistry 19, 144–152 (2020).
[3] Ustarroz, J et al. Journal of the American Chemical Society 135, 11550–11561 (2013).
[4] Hussein H. E. M. et al., ACS Nano 12, 7388–7396 (2018).
[5] Harniman R. L. et al., Nature Communications 8, 971 (2017).
[6] Bernal, M. et al. Electrochimica Acta 445, 20, 142023 (2023).
[7] Torres, D. et al. Journal of the Electrochemical Society 169, 102513 (2022).
[8] Torres, D. et al. Journal of Solid State Electrochemistry (2023). doi.org/10.1007/s10008-023-05760-y
[9] Torres, D et al. Manuscript in Revision