Reasons for polarization of electroplated electrodes in electric heating tubes

Reasons for polarization of electroplated electrodes in electric heating tubes

The so-called polarization refers to the phenomenon where the electrode potential deviates from its equilibrium potential when current passes through the electrode. Cathode polarization causes the cathode electrode potential to shift towards the negative direction; Anodic polarization causes the potential to shift in the positive direction. The greater the current density through which the electrode passes, the greater the absolute value of the electrode potential deviation from the equilibrium electrode potential. The deviation value can be expressed as overpotential or overpotential △ Δ. Generally, overpotential is expressed as a positive value, so cathode overpotential and anode overpotential.

The reason for the polarization of the electrode when energized is due to the slow speed of a certain step in the electrode reaction process. Taking the cathodic reaction process of metal ions reducing to metal on electrodes as an example, the reaction process includes the following three consecutive steps:

① Metal hydration ions move from the inside of the solution to the cathode interface - the transfer step of substances in the liquid phase;

② Metal ions obtain electrons at the cathode and interface, reducing them to metal atoms - electrochemical steps;

③ A metal crystal with metal atoms arranged in a certain configuration - the step of generating a new phase.

These three steps are continuous, but the speed of each step is different, so the speed of the entire electrode reaction is controlled by the slowest step.

The polarization caused by the diffusion rate of reactants or reaction products near the electrode surface being less than the electrochemical reaction rate is called concentration polarization. The polarization caused by the electrochemical reaction speed on the electrode being less than the electron motion speed in the external circuit is called electrochemical polarization or activation polarization.

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