I’m working with surface modified electrodes based on TiO2 mesoporous film coated on transparent FTO-Glass with a thickness of about 4 um.
Dear all,
Thank you very much for your kindly interest to replay on my question and to give me some
idea about surface area TiO2 mesoporous film.
I found recently that an other way to calculate the active surface of mesoporous TiO2 film is
to multiply the geometrical area of the TiO2 film (in my case aprox 0.5 cm2) with a "roughness factor".
This roughness factor is determined empirically. Some papers suggest a value around 100 per micrometer film thickness.
Best regards!
Dear Marius, i am also looking for the same instrument which can measure the surface area of thin films...
But as per my knowledge i did not find any.??....But for powders we have BET surface area technique......
One way could be, using afm. You can do lateral force microscopy with a charged tip. If you need more information, please refer to Prof. Udo D. Schwarz
Department of Mechanical Engineering and Materials Science, Yale University, New Haven, CT 06520 and his work. Hope this helps.
All the best,
Gopala Darbha
For surface area you have to measure BET. However, concerning the ACTIVE surface it depends very much on the pollutant
Dear sir,
what do you want to analyst?
1. Surface area of TiO2, it can be measured by BET analysis.
2. TiO2 active site, im not really sure about the method but AFM or SEM might be able to use.
I think this paper can help you.......http://plaza.snu.ac.kr/~eco/file/65.pdf
Dear Marius,
If you have a 5 by 5 square cm électrode with a thickness of about 4 microns, the total volume of the microporous layer (pore volume plus material volume) will be 10-2 cubic centimeters. It is totally unrealistic to use the usual BET method in that case unless you are ready to grind a large number of such electrodes.
If you want to measure surface area on thin films, it is tricky because you have very little sample. If the film is transparent you can go for ellipsometric porosimetry. You measure the pore volume and PSD from water adsorption desorption isotherms, and by modelling the pore system, you will be able to obtain the surface area. See http://pubs.acs.org/doi/abs/10.1021/la050981z. This is not a very common technique though, but it is commercial. You can also couple XRay Reflectometry with a controlled vapor pressure cell and obtain the same quantities, by measuring the shift in the critical angle (see http://www.lnls.br/PDF/sh04.pdf). Some of the techniques referring to mesoporous titania films are summarized here: http://pubs.rsc.org/en/Content/ArticleLanding/2012/NR/C2NR11817C.
If you want to measure the electrochemical active area of the electrode, you can do so by an UPD experiment of the films deposited onto Pt. See http://onlinelibrary.wiley.com/doi/10.1002/adma.200502215/abstract.
Good luck!
Dear all,
Thank you very much for your kindly interest to replay on my question and to give me some
idea about surface area TiO2 mesoporous film.
I found recently that an other way to calculate the active surface of mesoporous TiO2 film is
to multiply the geometrical area of the TiO2 film (in my case aprox 0.5 cm2) with a "roughness factor".
This roughness factor is determined empirically. Some papers suggest a value around 100 per micrometer film thickness.
Best regards!
to know exactly the active surface area of mesoporous TiO2 film, we need to use a mask which we know exactly the area. About the total exact area of the film we should know the porosity ,specific area and thickness of the film: porosity and specific area can be determine by BET measurement, thickness by alpha step machine, for thin film a few microns. We need also the density of TiO2, easy to know from literature. From all these parameter, you can calculate the exact area of your TiO2 film.
dear Marius can you give the reference article which tells measuring the active surface area of a thin films by measuring the ROUGHNESS and AREA parameters.
thanks in advance..
1. Solar Energy Materials and Solar Cells 55 (1998) 215Ð223
2. J Electroceram (2006) 17:929–932
3. J. Phys. Chem. B 2000, 104, 11449-11459
4. Langmuir 2009, 25(9), 5371–5379
5. Solar Energy Materials & Solar Cells 57 (1999) 107Ð125
These are the papers. Have fun by reading!
Best regards!
By simple BET it is difficult to mesure the surface area of only film. Method of roughness factor is much better.
Dear Damiàn,
There are at least two concerns about this CV method that you described.
1. You propose to make the calibration with TiO2 single crystall, which is, of course, crystalline phase of TiO2. Thus, this calibration will not be applicable for amorphous films of TiO2 prepared by wet chemical or electrochemical methods at low temperature. Moreover, one needs to be sure that the crystalline phase of the TiO2 sample under study is the same as the one used for calibration.
2. As it is nicely described in the manuscript, that you have attached, TiO2 is a semiconductor. The interfacial capacity of semicoductor/electrolyte interface consists not only of capacity of electrolyte double layer, but also of a capacity od deplition layer in TiO2. Both are proportional to surface area. But the capacity of deplition layer also depends strongly on other parameters, such as DOS of TiO2 (including surface states, dopant states etc.) and concentration of charge carriers. These parameters are more difficult to control. And, thus, simple measurements of CV currents can give you the results not at all accurate.
Of course, if one works with thin amorphous films, deplition layer capacity can be neglected, but then again, how can you calibrate its interfacial capacity?
Summing up, to distinguish between electrolyte capacity and capacity of deplition layer, one needs to perform full impedance analysis in various electrolytes.
I believe that ex situ methods, like electron microscopy, BET etc. are the best options, despite all limitations.
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