  A calorimeter was built to measure the heat from a porous capacitive working
electrode connected in a three-electrode configuration. This makes it possible
to detect differences between cathodic and anodic heat production. The
electrochemical cell contains a large electrolyte solution reservoir, ensuring
a constant concentration of the salt solution probed by the reference electrode
via a Luggin tube. A heat flux sensor is used to detect the heat, and its
calibration as a gauge of the total amount of heat produced by the electrode is
done on the basis of the net electrical work performed on the working electrode
during a full charging-discharging cycle. In principle, from the measured heat
and the electrical work, the change in internal energy of the working electrode
can be determined as a function of applied potential. Such measurements inform
about the potential energy and average electric potential of ions inside the
pores, giving insight into the electrical double layer inside electrode
micropores. Example measurements of the heat are shown for porous carbon
electrodes in aqueous salt solution.
