Place the emery paper on Al foil then press strongly up to 10MPa pressure, you can find the rough surface on Al foil.i guess it may have high adhesion nature than smooth Al electrode surface.

Thanks Joachim, we have tried with chemical polishing with acids and also NaOH and a combination as well. The thing is that the paste seems to be adhering well to the substrate before electrochemical testing, but starts detaching right after testing and that is actually what the electrochemical tests show (e.g. EIS).

I'm not sure if there is a sort of pretreatment for increased adhesion that can stand along the electrochemical life of the electrode, or rather, there should be a new component in the paste who undertakes the adhesion maintenance.

Dear Joachim,

Thanks for the useful papers. There are however differences in the methods used there and in my question.

There are different methods for supercap electrode preparation like: Paste method, CVD growth, Self-Assembly (sequential), Spray-Coating. In all of them it is tried to put a carbon layer on a metal current collector (the papers you sent mainly focus on the carbon material preparation and use a fabric like assembly of them directly as the electrode (as their titles suggest: Paper-based ultracapacitors ..) and do not focus on transfer method to a current collector).

In paste method, carbon species are first prepared through whatever method (arc, CVD, etc.) and then are mixed to make a paste or slurry that is in the next step cast on a metal foil. Here is where the adhesion story starts ..

Place the emery paper on Al foil then press strongly up to 10MPa pressure, you can find the rough surface on Al foil.i guess it may have high adhesion nature than smooth Al electrode surface.

Thank both of you K.P. and Steffen for the suggestions.

AN+Et4NBF4 electrolyte? Try other electrolytes!

Hi Xianzhong,

It's an aqueous electrolyte (Na2SO4) and I cannot use the organic ones.

You can't use aluminum current collector in aqueous electrolyte (Na2SO4), instead, the best choice is stainless steel(SS), for example, 304 SS.

Thanks again Xianzhong,

In practical point of view, SS is not the best choice for current collector of supercapacitors, because of weight, conductivity, contact resistance and other things. The particular material for traditional capacitors' current collector is Al and it can be wise to look also at supercaps the same way. Maybe SS can be useful for studying of the active material, but in real world I do not know how applicable this can be. Then, in corrosion point of view, Al should not suffer too much in neutral medium such as Na2SO4, just remains the adhesion issue that I think would be present for most of the electrolytes.

OK, I hope that my papers can be helpful for you. see:

[1] X. Z. Sun, X. Zhang, H. T. Zhang, D. C. Zhang, Y. W. Ma, J. Solid State Electrochem. 16 (2012) 2597-2603.

[2] X. Z. Sun, X. Zhang, H. T. Zhang, B. Huang, Y. W. Ma, J. Solid State Electrochem. 17 (2013) 2035-2042.

Of course Xianzhong,

Thanks a lot.

What about adding some surfactant to the paste mixture? Does any body think that the addition of something like CTAB, TWEEN, SPAN, Triton X-100 or other surfactants can help?

Nice meeting with you in Lausanne :) 

how is stability of Al in Na2SO4 solution, since the pH is almost neutral?. what polarities you use? do you observe pitting specially on positive current collector?- that was what we observed few years back. did you observe some corrosion products responsible for lack of adhesion later?- is adhesion an issue on both current collectors? did you try some alloy of Al may be?

Qamar 

Hi Qamar,

Nice to hear from you again after Lausanne and thanks for participating the discussion.

Honestly, we have not focused deeply on the corrosion of Al substrate. We either use the direct growth of active material (mainly CNTs) on Al for supercap (like these papers: Supercapacitor electrodes by direct growth of multi-walled carbon nanotubes on Al: a study of performance versus layer growth evolution AND Growth of carbon nanotubes on aluminium foil for supercapacitors electrodes) or the paste method. In case of growth method, we have not encountered the contact and adhesion problems of the CNTs to Al and so, we have not gone through the corrosion issue though it is definitely worth investigating. Especially, considering the point that our studies have been mainly focused on the material’s capacitive behavior and therefore, we have not gone through long and severe life cycling experiments. Although below 10K cycles the systems works reasonably, in longer cycles, maybe up to 100K, there is no guarantee that it remains as good as it was. So, it should be tried. The potential window in those cases (direct growth) is usually less than 1 V (0.7-0.8 V) and the collector is high purity Al. We didn't try other alloys and we didn't observe corrosion products or color changes on collector or separator. Pitting and other microstructural checks yet remain to be carried out in case we plan to monitor the longer cycling behavior of the system.

The problem of adhesion however, refers mainly to the paste method where even before starting the electrochemical characterization, the electrodes suffer from delamination and cracking. I have seen some works using special pretreatments on substrate with special conductive adhesives (like Electrodag EB-012) to enhance the adhesion of the paste to the substrate (see the suggestion by Steffen Schlueter in this discussion and his paper: Strategies to Reduce the Resistance Sources on Electrochemical Double Layer Capacitor Electrodes). Moreover, in our work, we do not prepare the active material as a separate film to be put on gold or Al current collector, but we try to cast it on the current collector to make it more realistic in practical point of view and more similar to a supercap electrode. Here is where the problem of delamination and cracking comes up even before the start of the characterization.

Have a good time

Mazdak

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Prof. Hashempour: We are also facing the problem of poor adhesion of carbon aerogel to the substrate? Did you figure out a solution to that?