AC impedance method is a very important method in electrochemical testing technology, which is an important means of studying electrode process dynamics and surface phenomena. Especially in recent years, due to the rapid development of frequency response analyzers, the testing accuracy of AC impedance has become higher and higher, and the impedance spectrum of ultra-low frequency signals has good reproducibility. In addition, with the advancement of computer technology, the automation of impedance spectrum analysis has become higher and higher. This enables us to better understand the double layer structure of electrode surfaces, activate passivation film conversion, induce, develop, terminate pore corrosion, and the adsorption and desorption process of active substances.
Both the linear polarization of the triangular wave scan and the linear polarization of the sine wave scan are based on the electrochemical linear polarization principle to measure the polarization resistance of the electrode system, and the polarization potential range of both is within the linear range (± 10mV OCP). Triangular wave scanning linear polarization is to apply a triangular wave scanning signal based on potential or current control to the system, and its scanning rate is generally 0.5mV/s to 5mV/s, and the polarization resistance Rp is calculated by dividing the polarization potential DE by the slope of the polarization current DI. Then the polarization current density Icorr is calculated according to Stern equation (2)
The CS series electrochemical workstation can be used for the testing of semiconductor or passivation film Mott-Schottky maps. By superimposing a fixed amplitude and fixed frequency AC disturbance signal at different DC potentials, the impedance values at different DC potentials are measured, and the depletion region capacitance Csc is calculated according to the imaginary part of the impedance. Finally, the Mott-Schottky diagram is calculated according to formula (1 or 2), and the carrier concentration in the semiconductor or passivation film material is calculated accordingly to determine the semiconductor characteristics of the material. Mott-Schottky formula:
1. Material preparation: supercapacitor material powder sample, polytetrafluoroethylene emulsion, conductive agent (acetylene black), binder, reference electrode, counter electrode, nickel foam, electrolytic cell, electrolyte. 2. Preparation process: Weigh sample powder, polytetrafluoroethylene emulsion, conductive agent and binder into a small beaker, mix evenly, repeatedly stir into paste, put into an oven at 80 ℃, bake into a semi-dry state, put into a tablet press, press into 150 ~ 300μm sheets, cut into 1cm2 electrode sheets, and put into an oven at 120 ℃ for drying. The dried electrode sheet was pressed onto nickel foam at 10MPa by a hydraulic press and used as a working electrode.