I am working on porous carbon for supercapacitor application. I need to now how supercapacity changes with porosity of materials.
Very interesting question, not clearly answered yet however. Micropores are pores producing the highest capacitance, but mesopores are useful for allowing diffusion of ions and therefore maintain a good capacitance even at high scan rate. Therefore, I would say that both micropores and mesopores are necessary. But this is true if an ideal capacitor is considered. You can get even higher capacitance through Faradaic effects, and some surface functions may allow this. But too many surface functions may also block the pore entrance, leading to a decreased capacitance and again there is an optimum to find. In summary, the good capacitance is a subltle balance between several effects.
Alain
Here is an interesting study on this subject. Take a look.
https://www.researchgate.net/publication/263087781_Porous_Carbon_for_Supercapacitors
I would strongly advice you to contact the author for further details.
Technical Report Porous Carbon for Supercapacitors
There are reports that capacitance at some materials increase with decreasing scan rate. The common reason given in literature is that, at porous materials, more ions can be stored in the pores over a long period of CV time (at slow scan rates). This increases the capacitance when the scan rate is slow.
The porosity of your carbon material may permit large capacitance especially at slow scan rates given that the pores are accessible to the ions. Look for papers on the dependence of capacitance on scan rate.
Very interesting question, not clearly answered yet however. Micropores are pores producing the highest capacitance, but mesopores are useful for allowing diffusion of ions and therefore maintain a good capacitance even at high scan rate. Therefore, I would say that both micropores and mesopores are necessary. But this is true if an ideal capacitor is considered. You can get even higher capacitance through Faradaic effects, and some surface functions may allow this. But too many surface functions may also block the pore entrance, leading to a decreased capacitance and again there is an optimum to find. In summary, the good capacitance is a subltle balance between several effects.
Alain
The interesting question. I have some experience for formation of the p/n junctions SiC/Si in porous silicon. Initual carbon felt (cloth) have to be impregnated with liquid silicon, then the carbon free phase (initual fibers) removed by long oxidation (1100 C, 2-3 days). We receive 100 mF/cm3 only, but I hope these experiments may be prolonged.
Sergey
Although there are many interesting papers but these papers provide the basic insight as to how pores affect the capacitance.
Hope these papers help you...
Good luck
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