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Electro chemical studies on lead acid batteries By M.SUDHEERA (Team Leader) K.SIVA PRASADA RAO (Member) P.ROHINIKUMAR (Member) Regional Center: 1353 RVR & JC College of Engineering (A) Cyclic Voltammetry (CV) Cyclic Voltammetry • Cyclic Voltammetry (CV) is a potentiodynamic electrochemical measurement that is generally used to study the electrochemical properties of an analyte in solution. • In CV, the electrode potential ramps linearly versus time are known as scan rates (Vs-1). • The potential is applied between the reference electrode and the working electrode and the current is measured between the working electrode and the counter electrode. Example for CV A cyclic Voltammogram is obtained by measuring the current at the working electrode during the potential scans. Consider the following reversible reaction: M+ + e- M The Cyclic Voltammogram graph resulting from the above single electron reduction and oxidation. Voltammogram of a Single electron oxidationreduction c d a b e g f From the graph • The reduction process occurs from (a) the initial potential to (d) the switching potential. In this region the potential is scanned negatively to cause a reduction. • The resulting current is called cathodic current (ipc). The corresponding peak potential occurs at (c), and is called the cathodic peak potential (Epc). The Epc is reached when all of the substrate at the surface of the electrode has been reduced. • After the switching potential has been reached (d), the potential scans positively from (d) to (g). This results in anodic current (Ipa) and oxidation to occur. • The peak potential at (f) is called the anodic peak potential (Epa), and is reached when all of the substrate at the surface of the electrode has been oxidized. Instrumentation A CV system consists of Electrolysis cell Potentiostat Current-to-voltage converter and Data acquisition system. The electrolysis cell consists of Working electrode Counter electrode Reference electrode and Electrolytic solution. • The working electrode’s potential is varied linearly with time, while the Reference electrode maintains a constant potential. • The Counter electrode conducts electricity from the signal source to the working electrode. • The purpose of the Electrolytic solution is to provide ions to the electrodes during oxidation and reduction. • A Potentiostat is an electronic device which uses a dc power source to produce a potential which can be maintained and accurately determined, while allowing small currents to be drawn into the system without changing the voltage. • The Current-to-Voltage converter measures the resulting current, and the data acquisition system produces the resulting Voltammogram. Applications • CV can be used to study qualitative information about electrochemical processes under various conditions, such as the presence of intermediates in oxidation-reduction reactions, the reversibility of a reaction. • Used to determine the electron stoichiometry of a system, the diffusion coefficient of an analyte (A substance whose chemical composition is to be determined by chemical analysis). • In addition, the concentration of unknown solution can be determined by generating a calibration curve of current vs. concentration.