here are two types of charge storage that can occur at the interface: pseudocapacitance and
double layer capacitance. For example, if the electrode is a carbon nanotube with some
functional groups on it or nanoparticles that allow interecalation of Li ions, then electron transfer reaction (Faradaic reaction) occurs at the surface of the electrode, and this type of capacitance is called ‘pseudocapacitance’. If no Faradaic reaction is allowed, charges can only be physically absorbed in to the double layer without any electron transfers. In this latter case we only have purely electrostatic double-layer capacitance. When we view the electrode/electrolyte interface
as a black box, we only see that ions and electrons enter and are stored at a given voltage, and it is difficult to distinguish whether charge is stored capacitively or Faradaically. The time scales and nonlinear response of each process is very different, however, so it is possible to separate
these processes from experimental data using suitable mathematical models.
Lecture 37: Pseudocapacitors and batteries 10.626 (2011) Bazant
Recall the Nernst equation:
For example, if R is the solid reactant, then for every reaction at the cathode,
charge of –ne is stored, which can be recovered by reversing the reaction. Let cR