Recently, Cholula-Díaz et al. [5] used aerosol assisted chemical vapor deposition to synthesize nanocrystalline graphite (NCG) thin films. The low nanoscale roughness of this material may lead to some insight into the electrodeposition process. Additionally, their complex electronic behavior may lead to the observation of new phenomena. These samples were used as working electrodes for silver electrodeposition. A single compartment electrochemical cell was used, with Hg|HgSO4 and a Pt wire as reference and counter electrodes, respectively. The composition of the platting bath was: 10 mM AgNO3, 1 M KNO3 and 1.6 M NH4OH [2].
Cyclic voltammetry experiments resulted in tilted voltammograms, which are typical of a high ohmic resistance. Since the platting bath had a high ionic concentration, this behavior is adscribed to the resistance of the NCG sample. The cell voltage U is equal to the sum of the double-layer potential φDL and the ohmnic drop.
U= φDL + iR
Hence, under potentistatic control, current changes result in variations of the ohmic term, to which the system responds by adjusting the double-layer potential to comply with the applied voltage value. This feedback loop between the double-layer potential and the current makes it difficult to establish a clear relationship between the experimental conditions and the characteristics of the deposited material. In contrast, galvanostatic control offers a far simpler scenario; since the current is fixed in the experiment, it is easier to determine the double-layer potential. Figure 1a shows the time evolution of the double-layer potential during controlled current experiments. The time scale on which the potential stabilizes is larger for the one observed for similar experiments on glassy carbon. This shows the importance of galvanostatic control as means to study electrodeposition samples with high resistivity. Figure 1b shows an SEM image in which submicrometric silver particles can be identified. We explore the dependence between the current pulses applied and the resulting particle size distributions.
References
- R. Unwin, Faraday Discuss., 172, 521 (2014)
- Miranda-Hernández, I. González, and N. Batina, J. Phys. Chem. B, 105, 4214 (2001).
- Richard L. McCreery, Chem. Rev., 108, 2646 (2008)
- J. Royea, T. W. Hamann, B. S. Brunschwig, N. S. J. Lewis, Phys. Chem. B, 110, 19433 (2006).
- L. Cholula-Díaz, J. Barzola-Quiquia, H. Krautscheid, U. Teschner, P. Esquinazi, Carbon, 67, 10 (2014).
Figure 1. a) Time dependence of nanocrystalline graphite electrode potential after applying cathodic current pulses from −50 to −325 µA in 10 mM AgNO3 + 1 M KNO3 + 1.6 M NH4OH electrolyte. b) SEM image (BS detector) of the surface of the nanocrystalline graphite showing particles of silver deposit.