Demonstration: Simultaneous Detection of Several Heavy

1. Demonstration: Simultaneous Detection of Several Heavy Metal Ions by Electrochemistry ( Anodic Striping Voltametry Pb 2+ + 2e Pb Cd 2+ + 2e Cd Cu 2+ + 2e Cu

2. How many electrodes? How do you name them? • 2. How does the potential on working electrode • determines the amount of metal deposit on and/or • striping away from working electrode? • 3. Is the counter electrode doing something during the depostion and • Striping? • 4. What would happen if there was no reference electrode?

3. Kinetics of Electrode Reactions (Chapter 3) p87 O + ne ⇄ R kdO ka kc kd R

4. Electric Charge Electric Charge Faraday constant: 96485 C/mol • Single electron charge: 1.602×10-19 C, 1C=6.24 ×1018 electrons • Electric current: I(A)=q( C )/t(s) • Relate electricity (charge) and chemistry (moles) together. N= q/nF (N is the moles of electron were involved in the electrochemical reaction). Moles of electrons relates the moles of reactant by the balanced equations chemical. Electrochemical reaction rate ( mol/s)= dN/dt= I/nF Heterogeneous reaction I: Current (Unit A , Ampere) i: current density(I/surface area) ( Note: Normally using A to denote surface area, the unit, cm2, ) Electrochemical reaction rate ( mol/s cm 2)= I/nF A=i/nF

5. Electrochemical reaction rate ( mol/s)= dN/dt= I/nF In order to keep the same denotions as in our book, we use i as current ( Unit A,ampere) and j as current density (i/surface area A) Electrochemical reaction rate ( mol/s)= dN/dt= i/nF Heterogeneous reaction ( Note: Normally using A to denote surface area, the unit, cm2, ) Electrochemical reaction rate ( mol/s cm2)= i/nF A=j/nF

6. Chapter 1, page 4.

7. Since the reaction rate is a strong function of potential, The aim of this chapter is to understand Potential dependent rate constant for accurate description of Interfacial charge-transfer dynamics

8. Electrode reaction rate (current) and surface concentration kf O + ne ⇄ R kb Reduction (cathode) Oxidation (anodic current) “0,t” here means that the concentration on electrode surface

9. Electrode reaction rate (current) and Electrode Potential O + e ⇄ R The Arrhenius Equation A: Frequency factor, k’: Boltzmann constant, h: Planck constant

10. This idea applies to electrode reactions too, but the shape of the curve would change as a function of the electrode potential. This is also the reason why changing electrode potential the reaction rate could change.

11. At equilibration Apparent Oxidation Apparent Reduction

12. E0’ at equilibration, Apply positive E to a new Value of E, the relative energy of the electron resident on The electrode changes by -F E= -F( E- E0’) Apply Positive E : transfer coefficient

14. Changing potential Equally impact on both reduction and oxidation More on oxidation More on reduction

15. Less or lower Gibbs energy for oxidation Higher Gibbs energy for reduction k0

16. Assume: Co*=CR*, E=E0’, kf Co*= kbCR*, kf = kb, E0’: formal potential of the electrode, at this potential, the forward and backward rate constants have the same value, which is k0, standard rate constant (or intrinsic rate constant)

17. Input kf and kb equation, then we got the following equation

18. At Equilibrium conditions: the exchange current C*: bulk concentration Nernst Equation Both sides are raised to - power C0*=CR*

19. The current overpotential equation

20. No Mass-Transfer Effects, the solution is well stirred When x is very small: ex= 1+ x Linear Characteristic at small 

21. Tafel behavior at large  At large negative overpotentials Empirical Tafel Constants

22. Homework: At large positive overpotentials Please get the relation equation between current i and  by youself.

23. Science 2003, 299, 1877