Example Questions Flashcards
EXAMPLE: Thermodynamics
EXAMPLE: Thermodynamics
Find electrode potential of metallic indicator
EXAMPLE: Thermodynamics
Write a balanced chemical equation and calculate the standard cell potential for the galvanic cell:
EXAMPLE: Dynamic electrochemistry
A current of 2 mA was measured due to proton reduction to hydrogen.
* How many molecules of H2 are being generated every second?
EXAMPLE: Electrochemical kinetics
EXAMPLE: Mass transport
EXAMPLE: Electrochemistry
Zinc metal reacts with aqueous hydrochloric acid to form zinc chloride in solution and hydrogen gas. Is this a redox reaction? If yes, identify the oxidizing agent, the reducing agent, and the substances being oxidized and reduced.
EXAMPLE: Dynamic electrochemistry
What do the terms ‘Galvanic cells’ and ‘Electrolytic cells’ mean? Given an example of each.
Galvanic cells: electrochemical cell which does work via spontaneous redox reactions Example: Discharging a battery.
Electrolytic: electrochemical cell in which we need to apply a voltage to do work on the system.
Example: charging a battery.
EXAMPLE: Thermodynamics
Explain in one sentence what the Nernst equation describes.
Relates equilibrium potential in non-ideal solution to that of an ideal solution.
EXAMPLE: Structure of the electrode interface
Draw the structure of the electrical double layer, according to the Gouy-Chapman-Stern model, at a negatively charged electrode surface in a solution containing only monovalent ions.
EXAMPLE: Structure of the electrode interface
The size of the electric double layer (EDL) at a charged interface can be described by the Debye length (1/𝜅), where:
1. Calculate the Debye length for an aqueous (𝜀0 = 78) KCl solution (concentration 100mM) at room temperature.
2. How would doubling the ionic strength change the Debye length?
3. How would you expect doubling the ionic strength to affect the capacitance of the electrical double layer?
- Na = Avogadro’s number
e = charge on a electron
n0 = concentration = Na*100 mM
𝜀 = permittivity of free space = 8.85×10−12 Cv-1m-1
T = temperature = 298 K
kb = Boltzmann’s constant = 1.380649×10−23 J/K
SOLVE
*2. Decrease debye length - No change*
EXAMPLE: Electrochemical kinetics
For a single electron transfer reaction at an electrode in which, α = 0.2, i0 = 4.0 × 10-6 A and concentration overpotential can be ignored, calculate the current flowing at overpotentials of +10 mV and +100 mV at 298 K.
EXAMPLE: Mass transport
Imagine you have developed a new CO2 reduction electrocatalyst, but efforts to characterise the kinetics of electron transfer are obscured by mass transport limitations. Describe (using diagrams where appropriate) three possible strategies for increasing mass transport to an electrocatalyst surface.
- Rotating disk electrochemistry
- Nanoscale electrochemistry
- Flow cell electrochemistry
- Fast scan CV
- Increasing temperature
- Generator collector electrochemistry
EXAMPLE: Mass transport
Consider a potential step experiment for the oxidation of 1 mM ferrocene (Fc) on a 1 mm diameter disk shaped Au electrode. The solution also contains 100 mM KCl as supporting electrolyte. The potential is stepped from a potential where no Fc was oxidized (0 V) to a potential at which Fc is oxidised at a diffusion limited rate (0.5 V). Draw concentration profiles (distance from electrode on the x-axis and concentration on the y-axis) normal to the electrode surface for Fc and Fc+ (the oxidised form the Fc) at three times, just before the potential step(t1), just after the potential step (t2) and a long time after the potential step(t3).
The current measured at the electrode during the potential step is given by the Cottrell equation.
Calculate the current at the electrode 2 seconds after the application of the potential step. Note the diffusion coefficient of ferrocene is 5 × 10-6 cm2/s.
n=1
F = 96485 C/mol
A = pi*(0.5 mm)^2 Cinf = 1 mM
t = 2 seconds
D = 5 × 10-6 cm2/s.
EXAMPLE: Cyclic Voltammetry
Draw the semi-quantitative i-E curve (cyclic voltammogram) for a solution containing 1 mM Fe2+, 1 mM Fe3+, and 2 mM Sn2+. Note the currents should reflect the relative concentration of the redox species. Assume equal diffusion coefficients for Fe2+, Fe3+, Sn2+ and Sn4+, and only consider these electrochemical reactions.
EXAMPLE: Cyclic Voltammetry
A flux of 2 × 10-6 mol s-1 cm-2 of CO2 was reduced to CO at a 5 cm2 working electrode in the three-electrode cell configuration with a SHE reference electrode and a Pt counter electrode. What current if flowing through the reference electrode? What current is flowing through the counter electrode?
EXAMPLE: Cyclic Voltammetry
