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Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2008 (English)In: Electrochimica Acta, ISSN 0013-4686, Vol. 53, no 5, 2188-2197 p.Article in journal (Refereed) Published
Abstract [en]

It is demonstrated that current oscillations can be observed during chronoamperometric and cyclic voltammetric experiments in solutions containing 0.4 M CuSO4 and 1.2 M citrate at pH 11 and 50 °C. The oscillations, which are shown to originate from local variations in the pH, result in the deposition of nanostructured Cu and Cu2O materials. It is concluded that the current oscillations are analogous to the previously described potential oscillations obtained under controlled current conditions in alkaline Cu(II)-lactate, -tartrate and -citrate solutions. Rotating disk electrode results clearly show that the reduction of the Cu(II)-complexes is kinetically controlled and that the rate of the reduction increases with increasing pH and temperature. It is also shown that the presence of a cathodic peak on the anodic scan in the cyclic voltammograms can be used to identify the experimental conditions leading to the spontaneous current (or potential) oscillations. Electrochemical quartz crystal microbalance results indicate that the cathodic peak stems from an increased rate of the reduction of the Cu(II)-citrate complexes due to a rapid increase in the local pH. This causes Cu2O rather than Cu to be deposited which, however, results in a decrease in the local pH and a decreasing current. In situ ellipsometry data confirm that Cu2O deposition replaces that of Cu in the potential region of the cathodic peak. The present findings should facilitate syntheses of nanolayered materials based on spontaneous potential or current oscillations.

Place, publisher, year, edition, pages
2008. Vol. 53, no 5, 2188-2197 p.
Keyword [en]
Current oscillations, Cu; Cu2O, Nanolayers, Local pH variations, Citrate
National Category
Inorganic Chemistry
URN: urn:nbn:se:liu:diva-14885DOI: 10.1016/j.electacta.2007.09.032OAI: diva2:25499
Available from: 2008-09-29 Created: 2008-09-29 Last updated: 2009-04-27
In thesis
1. Electric Fields for Surface Design and Chemical Analysis
Open this publication in new window or tab >>Electric Fields for Surface Design and Chemical Analysis
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the use of electric fields for evaluation and control of chemical systems. An electric field can result in the flow of charge across an interface between a metal and a solution, by means of chemical reactions. This interplay between electricity and chemistry, i.e. electrochemistry, is a field of crucial importance both within research and industry. Applications based on electrochemical principles encompass such diverse areas as batteries and fuel cells, pH electrodes, and the glucose monitor used by people suffering from diabetes.A major part of the present work concerns the use of static electric fields in solutions containing a non-contacted metal surface. In such a setup it is possible to control the extent of electrochemical reactions at different positions on the metal. This allows the formation and evaluation of various types of gradients on electrodes, via indirectly induced electrochemical reactions. This approach is a new and simple way of forming for instance molecular gradients on conducting surfaces. These are very advantageous in biomimetic research, because a gradient contains a huge amount of discrete combinations of for example two molecules. The basis for the technique is the use of bipolar electrochemistry. Briefly, a surface can become a bipolar electrode (an electrode that acts as both anode and cathode) when the electric field in the solution exceeds a certain threshold value, thereby inducing redox reactions at both ends. In our experiments, the driving force for these reactions will vary along the electrode surface. Since the result of an electrochemical reaction can be the deposition or removal of material from an electrode, bipolar electrochemistry can be used to create gradients of that material on a surface. In order to gain a deeper understanding of these processes, the potential and current density distributions at bipolar electrodes were investigated with different methods. Especially the use of imaging techniques was important for the visualization and analysis of the gradients. Using this knowledge, the formation of more complex gradients was facilitated, and the results were further compared to simulations based on simple conductivity models. These simulations also provided us with means to predict the behavior of new and interesting setup geometries for pattering applications.The other major part is more application driven and deals with the use of alternating electric fields for chemical analysis, a technique known as electrochemical impedance spectroscopy (EIS). In this work, EIS has been applied for the analysis of engine oils and industrial cutting fluids. Emphasis was placed on practical aspects of the measurement procedure, and on the evaluation of the results using statistical methods. It was for example shown that it was possible to simultaneously determine the amount of different contaminants in low conducting solutions. Generally, EIS is used to measure the impedance of a solution or a solid, often as a function of the frequency of the alternating electric field. The impedance of a system is closely correlated to its complex dielectric constant, and EIS can therefor be used to examine many chemical and physical processes. It is further well suited for characterizing low conducting media with little or no redox-active species. The evaluation of impedance data is often a quite complex task, which is why we have made use of statistical methods that drastically reduce the effort and quickly reveal significant intrinsic parameters.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 50 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1206
Electric fields, Surface design, Chemical analysis, Bipolar electrodes, Impedance spectroscopy
National Category
Inorganic Chemistry Physical Chemistry Physical Chemistry Physical Chemistry
urn:nbn:se:liu:diva-12485 (URN)978-91-7393-819-8 (ISBN)
Public defence
2008-10-02, Planck, Fysikhuset, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2008-09-29 Created: 2008-09-08 Last updated: 2009-05-18Bibliographically approved

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