Capacitances of Porous Carbon Materials and Their Associated Electrode Layers

2 Capacitances of Porous Carbon Materials and Their Associated Electrode Layers 

Regarding the differential capacitance of such an electrode matrix layer, the Gouy-Chapman-Stern (GCS) double-layer modeling for capacitance is still applicable if fhe concenfrafion of fhe elecfrolyfe used is high enough to make the diffuse layer disappear. However, if a very dilufe electrolyte solution is used, the situation will become more complicated due to the potential distribution within the electrolyte channels inside the porous layer. 

In supercapadtors, the electrolyte concentration is normally high ( 1.0 M), causing the diffuse layer to disappear and fhe Helmholfz layer to remain. This increases fhe capacifance of fhe elecfrode layer and allows more charge storage. Furfhermore, if fhe material particle size is larger fhan fhe thickness of fhe Helmholtz layer ( 1 nm), conclusions derived from the planar electrode may still be applicable to the situation of particles. For example, the carbon particle materials used in supercapacitors are normally 10 to 50 nm—much larger than the thickness of the Helmholtz layer of 1 nm. 

To express fhe capacitance of such a high surface electrode material, a specific capacifance (Q, expressed in F.g i) is defined as  

Theoretically, we should be able to calculate the specific capacitance of an electrode material according to its mass in the matrix layer, its differential capacitance density (Q, in F.m ), and the total specific surface area of the carbon particles. In normal conditions, this surface area can be measured by the Brunauer-Emmett-Teller (BET) technique and expressed as in square meters per gram (m. g i)  

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