Experimental Coursework 3. Tuesdays, 14th, 21st  and 28th  March (spare week 11 – 4th  April). Students will be split in 2 groups of 3-4 students each. Each group carries out their own set of

experiments and then shares data with the other group. Every student has to carry out their own data analysis (except for equivalent circuit fitting) and write their own individual report.

Time: 10am - 3pm         Place: G29

CW3 Title. Characterisation of semiconductor electrodes for photocatalysis

Photocatalytic water splitting allows for the clean, low-cost production of H2  through the use of light energy. Worldwide, there has been a shift towards renewable, sustainable energy generation, and  so, methods like photocatalytic water splitting are of great interest. Research continues to find

new/modified photocatalytic materials to improve the efficiency. Hence, careful consideration of the materials characteristics is required.

You will be working to determine several characteristics of different electrode materials:

•    bandgap;

•    flat band potential;

•    donor concentration;

•    photocurrent onset potential;

•    charge transfer resistance (dark and light).

Prepare in advance by studying the materials and papers uploaded under Week 5 of the Module Content on QMPlus. Read up on how to determine the parameters listed above with the methods  you are going to use (see below).

Complete the following experiments for two different materials (one for each group). The samples have already been prepared for you.

UV-vis spectroscopy

•    Insert the bank substrate of the material you have been given into the cuvette slot. Ensure that the sample remains upright and is perpendicular to the beam with the substrate facing the incident light (arrow shown on cuvette holder). Close the lid.

•    Click on the ‘Blank Cuvette’ measurement icon at the top.

•    Now remove the blank sample and insert the sample to be measured.

•    Select the ‘Measure’ icon.

•    Open the Mars analyser for the last measurement and select the spectrum tab.

•    Now open ‘table view’ from the drop down on the right-hand side ensure that ‘all wavelengths’ is selected.

•    Export the data to excel/ notepad.

•    Save data to a memory key.

Electrochemical characterisation

1.   Mott-Schottky Analysis

•    Fill the chamber (already assembled for you) with 0.1 M Na2SO4  solution ensuring that no air bubbles get trapped within the O ring.

•    Clamp the chamber into position above the lamp within the Faraday cage.

•    Connect the counter and reference electrodes to the corresponding wires (shown on the mousepad).

•    Ensure that the electrodes are in the electrolyte and add more if required.

•    Close the Faraday cage.

•    On the computer open ‘ Experiments > Impedance > Mott Schottky.

•    A list of parameters will open. Set the ‘Initial voltage’ to -0.8 V and ‘final voltage’ to 0.8 V step size of 0.1 V, AC voltage to 10 mV rms and the frequency to 1 kHz,

•    Ensure to fill in the ‘Output File’ name the file with something you will remember before selecting ‘OK’ .

•    After the measurement is complete open the data by clicking on F2_SKIP and then the analysis tab select your data file from the list (should be the top one) and the analysis   software will open.

•    To save the data click the table icon and then copy the data to either excel or notepad.

•    Save data to a memory key.

2.   Linear sweep voltammetry (LSV)

•    Open Experiment > Physical Electrochemistry > Linear Sweep Voltammetry Again, a list of parameters will open, set the following for each material

•    Set the other parameters scan rate (10 mV/s), step size (1 mV), max current (0.5 mA)

•    Complete the LSV in the dark and then again in the light

•    Use the ‘overlay’ function in the analysis software so that you can see the two graphs at once and determine the photocurrent onset potential for your material.

•    You will need this value for the next section

•    Save the data as before.

3.   Electrochemical impedance spectroscopy (EIS)

•    Open Experiment > Impedance > Potentiostatic EIS

•    Set the DC voltage to a value above the photocurrent onset potential that you just determined, use something that is approximately 0.5 V – 0.8 V above this value.

•    Set the other parameters as follows, frequency range (10-1 - 105  Hz), points/decade (10)

•    Complete a measurement in the dark

•    After the measurement open the data in the analyser software and select the impedance tab

•    Open the Impedance Model Editor and create an equivalent circuit for the system (you need to search the literature to find out what equivalent circuit is appropriate for your system!)

•    Once you have completed this select the compile icon (this will tell you if your circuit works) and then save it.

•    Go back to the data and again select the impedance tab this time click Impedance Fit by Simplex model and then select your equivalent circuit file

•    Determine the parameters that best fit your data and make sure you save the values.

•    Once you are happy save the data as before ensuring that the Fit lines are also saved.

•    Now complete the measurement again with the lamp on and fit to your equivalent circuit as before.

•    Save the data as before.