| dc.description.abstract | The reversible heat of electrical double layer (EDL) formation in porous carbon has been
investigated several times since 2006, typically by measuring the combined heat production of
the anode and the cathode in an electrochemical cell. In this work, the heat of EDL formation is
instead determined at one electrode. Our aim is to use this approach to determine the EDL
formation heat for one type of counterion at a time.
To measure the EDL formation heat at one electrode, two calorimetric setups are built, both of
which contain a three-electrode cell in which only the heat generated at the working electrode is
measured. The first setup uses thermometers to conduct a temperature difference measurement,
while the second measures the heat directly using a heat flux sensor.
The reversible heat, which is the heat of EDL formation, can be separated from the irreversible
heat by comparing the total measured heat during charging and discharging. Results obtained
with the temperature difference measurement setup show that the heat of EDL formation is
higher with chloride or fluoride counterions than with sodium counterions. This is ascribed to different ionic
radii giving rise to different entropic changes during EDL charging. A simple, exclusively
entropic model is developed based on this concept. It is capable of reproducing the experimental
results with reasonable ionic radii and micropore volume as input. Accounting for the ionic radii
appears to be necessary to explain the difference in EDL formation heat between sodium
counterions and chloride or fluoride counterions. | |
