Electrode potential is a very important concept in electrochemistry, and it is also a concept often used in the study of electrodeposition process . It refers to the measured potential relative to the reference electrode when the metal is immersed in the solution containing the metal salt as an electrode and an electric double layer is formed on the surface.
Electrode potential is the electrode characteristic exhibited when metal ions enter the electrolyte solution and arrange on the metal surface to form electric double layer. From the structure of the electric double layer, we can infer that the side of the metal electrode surface in the electric double layer and the side where the dissimilar ions in the solution are arranged are equivalent to a parallel plate capacitor, and there is a potential difference between the two electrodes. However, the absolute value of this potential cannot be directly measured at present, and can only be measured by indirect methods. In the standard state (25 ° C, 1mol/L concentration), each metal has a stable electrode potential, which is the standard electrode potential. When an electrode reaction occurs, such as electrodeposition, the potential of the metal electrode changes. After studying the factors that affect the change , the German physical chemist Walter Nernst (Walther Nernst, 1864-1941) proposed an equation for calculating the electrode potential, which is the famous energy in electrochemistry The Stern equation, also known as the electrode potential equation:
The electrode potential equation mentioned here is used to calculate the actual . Because the state of the electrode in actual work is rarely the standard state. Especially in the electrodeposition process, in addition to the main salt ions of the deposited metal, many auxiliary agents and additives are added to Sometimes the temperature reaches above 60 °C, and the potential value of the electrode will definitely deviate from the original standard potential. And many times we hope that the potential of the electrode will have a certain deviation in the direction we need, which we call polarization. A certain polarization is advantageous for some electrodeposition processes. Such as electroplating process or electroforming process. By adding a complexing agent or other additives, two metals whose standard electrode potentials are far apart can be close to each other in a specific plating solution, so that they can be co-deposited into alloys. This is principle of alloy electroplating. Of course, in the electrometallurgical process and most anode processes, polarization is undesirable, because polarization means increased consumption of electrical energy or certain undesirable reactions.
