Electrodeposition of Cobalt Nanoclusters From Ammonical Chloride Solutions Onto Hopg Electrodes. A Kinetical and Morphological Study

Abstract

A kinetical study about the Co electrodeposition onto Highly Oriented Pyrolytic Graphite electrodes from an aqueous solution containing 0.01 M CoCl 2 + 1 M NH 4 CI (pH = 7) was conducted at overpotential conditions through potentiostatic studies. The entire chronoamperograms were adequately predicted, considering the contribution to the total current of three different processes: a Langmuir-type adsorption process, a three-dimensional nucleation and growth and a proton reduction process. In all cases, the nucleation rate and the number of active nucleation sites are potential dependent. The Atomic Force Microscopy study revealed the presence of homogeneous cobalt clusters of less of 100 nm in height and 50 nm in diameter at different potential values.Keywords: cobalt; nanoclusters; HOPG; kinetics; AFM; MFM. INTRODUCTIONMaterials based on cobalt have attracted a considerable attention due to their magnetic properties, which can be used in the production of sensors, heterogeneous catalysts, intercalation compounds for energy storage, magnetooptic recording media, among others.1-8 Specifically, the magnetic properties of isolated cobalt particles change considerably as their sizes enter the nanometer range because they exhibit a large magnetic coercivity, which may be employed to fabricate high density magnetic memory devices.9-15 Thus, it is not so strange that different methodologies are being developed to produce magnetic cobalt nanoclusters with controlled size and morphology. [16][17][18][19][20][21] Probably, high vacuum methods, 22 and thermal decomposition 23 have been the preferred techniques to prepare monodisperse magnetic cobalt clusters onto different substrates. But, recently, electrodeposition is being recognized as an useful technique to produce cobalt nanoparticles. Also, it is important to highlight that electrodeposition is a simple electrochemical technique, which can be implemented at room temperature under ambient conditions. Moreover, these features make electrodeposition a non-expensive technique easily scalable to the industrial level. However, a good knowledge of the kinetic parameters involved during the electrodeposition process is required to achieve a precise control of the cobalt nanoclusters synthesis. In this sense, sulfate solutions have been the preferred systems to electrodeposit cobalt nanoclusters, [24][25][26][27][28][29][30] Although chloride solutions are widely employed for studying the cobalt electrochemistry, these plating baths have been scarcely used to electrodeposit cobalt nanoclusters. Probably, it is because chloride ions induces stress on the cobalt deposited, 31 and may interact strongly with Co adatoms yielding drastic changes on the deposit morphology.32 Nevertheless, chloride electrolytes allow to get a higher electrical conductivity in the electrolyte, lower overpotential for cobalt deposition, and higher cathodic current efficiency.31. These features of chloride plating baths might diminish the cost related to the synthesis of cobalt nanoclusters by ...