Pseudocapaciteit

Pseudocapacitance is a phenomenon observed in electrochemical energy storage devices, particularly supercapacitors, that exhibits characteristics of both batteries and conventional capacitors. Unlike electrostatic charge storage in electric double-layer capacitors (EDLCs), pseudocapacitance arises from fast, reversible faradaic (redox) reactions occurring at the surface or near-surface of electrode materials. These reactions involve the transfer of electrons and ions, leading to a higher energy density compared to EDLCs, which store charge purely through ion adsorption.

The key feature of pseudocapacitance is the rapid nature of these redox processes, allowing for high power densities comparable to EDLCs. Common electrode materials that exhibit pseudocapacitance include transition metal oxides, hydroxides, and conductive polymers. For example, metal oxides like ruthenium oxide (RuO2) and manganese dioxide (MnO2) undergo surface redox reactions that contribute significantly to the overall capacitance. Similarly, conductive polymers can undergo doping and de-doping processes that involve faradaic charge transfer.

The capacitance value in pseudocapacitive materials is often dependent on the electrode potential, exhibiting a shape in cyclic voltammetry (CV) curves that deviates from the rectangular shape characteristic of EDLCs. These curves show peaks corresponding to the redox transitions. While pseudocapacitance offers advantages in energy density, the cycling stability can sometimes be a challenge due to the chemical transformations involved in the redox reactions, although significant progress has been made in developing more robust pseudocapacitive materials.