KJM 3110 Electrochemistry

Lab 1-4

Review 2020

Most figures from the textbook we use for the course, via its web resources:

Lab 1

a. Daniell cellb. Electrosynthesis – Ni deposition

c. H2 evolutiond. Diffusione. pH meter

1a. Daniell cell

• Questions and learning outcome:

• Why do we measure too low values?

• Use much bigger differences in concentration!

• Measure the voltage while loaded by the LED. Cause of losses?

• Exercise similar to one in Physical chemistry – make connection, step up.

1a. Daniell cell

• E (V) in the Pourbaix is the voltage on the WE

• Stirring removes concentration polarisation• Gives higher currents at constant polarisation voltage (2 V).

b. Electrosynthesis - Ni deposition

c. H2 evolution by H2O electrolysis

• 2H+ + 2e- = H2(g)

• EpH=7 vs SHE = -0.414 V

• EpH=7 vs SCE = -0.414 – 0.241 = -0.655 V

• KNO3 supporting electrolyte decreasesohmic overpotential

• Pt > Ni > FTO

• (What goes on at the CE?)

• 2H+ + 2e- = H2(g)

• Reductive transfer coefficient ≈ 0.1

c. H2 evolution by H2O electrolysis

• Learning outcome

• «… the Tafel analysis proved to be challenging as it conflicted with the primary observations.”

c. H2 evolution by H2O electrolysis

d. Diffusion coefficient for the oxidised species in the [Fe(CN)6]

3- / [Fe(CN)6]4- redox couple

• Everyone understood and applied correctly theCottrell equation

• Diffusion coefficients covered 4 orders of magnitude

• Used different parts of the curve – rarely linear

• Our experimental setup far from ideal

• Geometry

• Convection

• Reversible RE (CE)

• Az+outer = Az+

inner

• Ion selective membrane

• Very high impedance

e) Ion-selective membranes and electrodes. The pH meter

Lab 2

2.1 Chapter 10 Electrode polarization

Trough cells

• 11 mM Cu(NO3)2• Conductivity 0.28 S/m

• Resistivity 3.6 Ωm

• Cell resistance 188 Ω

• + 1 M KNO3• Conductivity 14.8 S/m

• Resistivity 0.068 Ωm

• Cell resistance 3.6 Ω

• Add conductivities or conductances, not resistivities or resistances

2.1.1 Ohmic polarisation

• All three…

2.1.2 Kinetic polarisation

• Rct = 1.8*105 ohm or 180 ohm?

• Can be calculated into ASR, butnot resistivity

• Ohm*m2 or ohm*cm2

2.1.2 Kinetic polarisation

• 4.84 mV

2.1.3 Transport polarisation

2.1.4. Combined polarisations

• Ambiguousinterpretation of Tafel plots

2.2 Excercise for Ch. 11 Corrosion

2.3 Excercise for Ch. 12 Steady State Voltammetry