BAI XUE COULY CEDRIC DUARTE RODRIGUEZ ALEJANDRO LE PHU THIEN WIZNER AGNIESKA

SUPERCAPACITORS

During this practical we will measure the Capacitance of 4 different Electrochemical Capacitors with 3 different ways:

1/Electrochemical Impedance Spectroscopy 2/Cyclic Voltammetry

3/Galvanostatic Charge and Discharge How it works? Electrochemical Impedance Spectroscopy: apply one potential with one frequency and we measure the current returned. Cyclic Voltammetry: the working electrode potential is ramped linearly versus time. We measure the current returned. Galvanostatic Charge and Discharge: charge and discharge of the swagelok with the same working electrode's current, here 2mA. Goal of this practical:

Measure the Capacitance of the 4 cell, Effect of the concentration of the solution,

Effect of the radius of the cation dissolved in the solution, Compare the result of the different solution.

1/Electrochemical Impedance Spectroscopy

Experiment: 4 different solutions.

Electrolyte HCl 1M HCl 3M KCl 1M KCl 3M

Mass of carbon layer (mg)

25.2 21 23.3 29

So 4 different swageloks. Each of them have 2 electrodes of gold and 1 carbon layer between the electrolyte and each electrode.

Draw of one swagelok

Results To obtain the capacitance from the EIS, you must take the value of the frequency and the resistance from the point which has the lower frequency (right part on the Nyquist Diagram).

Graph to explain how to take the value of impedance

HCl 1M:

f (Hz) 1.00E-003

Z'' () 45.56

Mass carbon (g) 0.03

C (F) for the device 3.41

C (F.g-1) 135

HCl 3M:

f (Hz) 1.00E-003

Z'' () 30.3

Mass carbon (g) 0.03

C (F) for the device 5.25

C (F.g-1) 250

KCl 1M:

f (Hz) 1.00E-003

Z'' () 43.52

Mass carbon (g) 0.02

C (F) for the device 3.65

C (F.g-1) 157

KCl 3M:

f (Hz) 1.00E-003

Z'' () 29.5

Mass carbon (g) 0.03

C (F) for the device 5.39

C (F.g-1) 186

2/Cyclic Voltammetry

Graph of charge and discharge in cylic voltammetry,

To calculate the slope we choose the point of maximum charge Point 1 and his homologue Point 2 n.b: Q discharge is in C or A.s , we don't need to multiply by 3600 as we have in the support HCl 1M:

Slope (As.V-1) -0.42

C capacitance gravimetrique (F.g-1) 32.9

HCl 3M:

Slope (As.V-1) -0.79

C capacitance gravimetrique (F.g-1) 75.23

KCl 1M:

Slope (As.V-1) -0.29

C capacitance gravimetrique (F.g-1) 24.89

KCl 3M:

Slope (As.V-1) -1.19

C capacitance gravimetrique (F.g-1) 82.06

3/Galvanostatic Charge and Discharge characteristic

Graph to explain how to calculate the slope

HCl 1M:

Slope (V.s-1) -3.58E-003

C capacitance gravimetrique (F.g-1) 44.33

HCl 3M:

Slope (V.s-1) inexploitable

C capacitance gravimetrique (F.g-1) inexploitable

KCl 1M:

Slope (V.s-1) -4.10E-003

C capacitance gravimetrique (F.g-1) 41.87

KCl 3M:

Slope (V.s-1) -3.31E-003

C capacitance gravimetrique (F.g-1) 41.67

Discussion

All the measure are in F.g-1

EIS CV GCD Average capacitance

HCl 1M 135 33 44 71

HCl 3M 250 75 / /

KCl 1M 157 25 42 74

KCl 3M 186 86 42 105

We can conclude that when we increase the concentration for one solution we increase the capacitance. Because we have more atoms stuck on the electrode, so more exchangeable charge. From public data, the value of capacitance of Supercapacitors is approximately 150-250 F.g-1, as we can see we have the same value for EIS experiment but for CV and GCD we have the value that are 3-4 times lower. Thus, we can conclude that EIS method is more accurate than the 2 other methods