Hello everybody
I measured BET surface area and Electrochemically active surface area (EASA) of synthesized MnO2 nanomaterial. EASA was obtained by using Cyclic voltammetry at different scan rates (considering slope (Cdl) by plotting current (mA) vs. scan rates (mV/s)). the slope was obtained to be 0.0487 mF. Here, the carbon clothes (1 cm2) was used as a substrate for MnO2 nanomaterial, and considered Cs = 0.02 mF/cm2. EASA calculated from Cdl/Cs. The mass loading of the MnO2 on carbon cloth was about 0.00036 g/cm2.
1- First question is that "considering Cs=0.02 mF/cm2 as specific capacitance of an atomically smooth carbon meterials" is correct?
2- Second question is that : The BET surface area of MnO2 was obtained to be 17.5 m2/g. But EASA was obtained to be 0.0487 mF (slope), 2.435 cm2 (from Cdl/Cs), and 0.68 m2/g. Why there is high difference between obtained BET surface area (17.5 m2/g) and EASA (0.68 m2/g). Is there somethings wrong with the EASA result or it is correct?
I will be thankful if you could help me regarding two above questions.
Thank you
Your measurements are what one would expect. BET will probe the entire surface area available to N2 gas (at - 196C) - ~ 14 Angstroms2 - and this includes the meso- and macropores. Your active surface area will be much smaller than this.
Always believe what a calibrated/verified instrument delivers.
Your measurements are what one would expect. BET will probe the entire surface area available to N2 gas (at - 196C) - ~ 14 Angstroms2 - and this includes the meso- and macropores. Your active surface area will be much smaller than this.
Always believe what a calibrated/verified instrument delivers.
I do not know the method you used for measuring EASA. I use the CV PdO reduction peak in my work. Yet, it is usually valid that the EASA is much less than BET area. The BET area measures the physiosorption of N2 through the Van der Waals force, but EASA results from the chemical reaction between the electrode and electrolyte.
BET surface area is widely accepted method than other. It is very difficult to set relation between these two method. Because two methods are completely different experimental set up.
More than one layer formed in BET surface . but only mono layer in electrochemically active surface.ln this layer electrochemical attraction between adsorbent and adsorbates
Dear All
I am really thankful for your nice explanations
With regards
Alireza Valipour Note that the statement above 'More than one layer formed in BET surface' is incorrect. The back-extrapolation to zero pressure (for calculation of SSA) is assumed to be a monolayer although further layers can, of course, be added (and this is seen in the slope of the isotherm) but not used in the SSA calculations. See Gregg and Sing: Adsorption, Surface Area and Porosity
Hello@Alireza Valipour
Here, i am giving explanation from my concern that about your question..
I use the CV PdO reduction peak in my work. Yet, it is usually valid that the EASA is much less than BET area. I do not know the method you used for measuring EASA. The BET area measures the physiosorption of N2 through the Van der Waals force, but EASA results from the chemical reaction between the electrode and electrolyte. BET surface area is widely accepted method than other. It is very difficult to set relation between these two method. Because two methods are completely different experimental set up. Always believe what a calibrated/verified instrument delivers. Your measurements are what one would expect. BET will probe the entire surface area available to N2 gas (at - 196C) - ~ 14 Angstroms2 - and this includes the meso- and macropores. Your active surface area will be much smaller than this.
With best regards,
Yedluri Anil Kumar
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