Electrochemical Methods - II (Contd.)

This paragraph introduces the topic of electrochemical methods, focusing on the impact of electric current on solutions, specifically electroactive solutions within electrochemical cells. It discusses the importance of understanding how current affects these solutions and the corresponding cell potential (E0). The paragraph also touches on the difference between galvanic and electrolytic cells, and the significance of the Nernst equation in calculating the cell potential and understanding the relationship between current passage and cell potential. The concept of bulk electrolysis is introduced, along with techniques like electrogravimetry and coulometry, which are used to measure changes in mass due to current passage.

This paragraph delves into the need for modifications to the Nernst equation when dealing with current passage in electrochemical cells. It highlights the importance of considering the IR drop and polarization effects when operating an electrochemical cell. The discussion includes the necessity of applying a potential higher than the thermodynamic potential to generate current in the cell. An example involving the determination of cadmium in HCl solutions using electrogravimetry or coulometry is provided to illustrate the concepts. The paragraph emphasizes the need to understand cell arrangement and the impact of the applied potential on the reduction and oxidation processes.

This paragraph focuses on the concept of ohmic potential, which is a result of the current multiplied by the resistance in the cell. It explains the need to apply a potential more negative than the thermodynamic cell potential to generate a current in the cell. The paragraph discusses the calculation of the required applied potential based on the cell's resistance and current. It also touches on the concept of IR drop compensation in modern instruments used for cyclic voltammetry measurements, highlighting the importance of minimizing IR drop for accurate current measurement.

The paragraph discusses strategies to reduce cell resistance and polarization effects in electrochemical measurements. It explains how adding supporting electrolytes with high ionic strength can reduce cell resistance and consequently the IR drop. The paragraph also introduces the concept of a three-electrode system, which is useful for minimizing IR drop and polarization effects. The discussion includes the use of an auxiliary or counter electrode to ensure that the current passes primarily through the working electrode, thus reducing the impact of the reference electrode on the current. The paragraph emphasizes the importance of maintaining high ionic strength and the use of an auxiliary electrode to minimize IR drop and polarization effects.

This paragraph explores the relationship between the applied potential (E app) and the resulting current (I) in an electrochemical cell, considering the effects of IR drop and polarization. It describes how the current plotted against the applied potential shows a linear relationship up to a certain point before deviation occurs, indicating the onset of polarization effects. The paragraph explains the calculation of the polarization effect (Pie) and how it contributes to the overall potential required to achieve a specific current. It also differentiates between concentration polarization and kinetic polarization, discussing their impact on the electrode reactions and the importance of mass transfer processes like diffusion, migration, and convection in maintaining the cell's performance.

The final paragraph discusses the factors influencing mass transfer and electrode reactions in an electrochemical cell. It explains the role of concentration gradients, diffusion, migration, and convection in the mass transfer process. The paragraph highlights the importance of ensuring that the reactants reach the electrode surface efficiently, which is dependent on these mass transfer processes. It also touches on the concept of overvoltage and the need to overcome it through activation energy. The discussion concludes with practical considerations for using supporting electrolytes to reduce IR drop and improve the efficiency of electrochemical techniques like electrogravimetry.