EIS

Question 1

Advantages of EIS over dc techniques

Answer 1

• Use of very small excitation amplitudes (minimal perturbation)
• Information on both electrode capacitance and resistance
• Polarisation and solution resistance can be separately resolved

Question 2

What is EIS?

Answer 2

• Three electrode cell
• working electrode (electrode of interest), counter electrode and a reference electrode
• polarization applied by potentiostat ac sine wave of small amplitude
• ac current detected using two phase sensitive detectors in a quadrature
• by knowing potential amplitude and the ac current in phase and 90’ out of phase, the impedance of the working electrode can be described completely as a function of the frequency

Question 3

What is impedance?

Answer 3

• For ac theory where frequency is non zero, E^=I^ x Z which is analagous to V=IR
• Impedance (Z) is the equivalent of resistance
• resistor and capacitors impede the flow of electrons in an ac circuit

Question 4

Impedances in series

Answer 4

• Impedances added together

- Dominated by the largest individual impedance

Question 5

Impedances in parallel

Answer 5

• Impedances added reciprocally

- Dominated by the smallest individual impedance

Question 6

Impedance plot analysis

Answer 6

-Perform measurements on the circuit and analyse the resulting impedance plot

Question 7

Advantages of Bode plot over Nyquist

Answer 7

• Since frequency appears on one of the axes its easy to understand from plot how impedance depends on frequency
• Use of log frequency allows a wide freq range
• This is and advantage when impedance depends strongly on the frequency

Question 8

Resistors

Answer 8

Z = R

Question 9

Capacitors

Answer 9

Z = -j/wc