电化学基础 4.pptVIP

(1.24) (1.25) 1.4.3 Square-Wave Voltammetry (方波伏安法) Figure 1.20 Figure 1.21 1.5. AC Voltammetry （交流伏安法） Figure 1.22 (1.26) 1.6. Stripping Analysis（溶出分析） Two-step technique: Deposition + Stripping 1.6.1 Anodic Stripping Voltammetry (ASV，阳极溶出伏 安法) Deposition Stripping Figure 1.23 For a mercury film electrode, the peak current is given by For a hanging mercury drop, the peak current is given by (1.27) (1.28) 1.6.2 Potentiometric Stripping Analysis (PSA，电势溶 出分析) (1.29) Advantage: The use of nondeaerated sample represents an important Advantage of PSA. Figure 1.24 1.6.3 Adsorptive Stripping Voltammetry and Potentiometry Figure 1.25 1.6.4 Cathodic Stripping Voltammetry（阴极溶出伏 安法） 1.7 AC Impedance （交流阻抗法） Large perturbation on the system- far from the equilibrium! To perturb the cell with an alternating signal of small magnitude and to observe the way in which the system follows the perturbation at steady state. Advantages: (1) an experimental ability to make high-precision measurements because the response may be indefinitely steady and can therefore be averaged over a long term, (2) an ability to treat the response theoretically by linearized (or simplified) current-potential characteristics, (3) measurement over a wide time (or frequency) range (104 to 10-6 s or 10-4 to 106 Hz). 1.7.1 Types of Techniques 图1.26 A bridge circuit for measurements of electrochemical impedance The technique where the cell or electrode impedance is plotted vs. frequency is called electrochemical impedance spectroscopy (EIS). Lock-in amplifiers or frequency-response analyzers 图1.27 Schematic diagram of apparatus for an ac voltammetric experiment. 图1.28 Phasor diagram for an alternating voltage, e=E sin?t 图1.29 Phasor diagram showing the relationship between alternating current and voltage signals at frequency ? 图1.30 Impedance plot for an electrochemical system. Regions of mass-transfer and kinetic control are found at low and high frequencies, respectively * * Part II El