1) I have seen several papers that using H2SO4 during the electrodeposition of Pt on ITO glass (H2PtCl6+H2SO4).
2) In the case of the methanol electrooxidation for the applied reaction, many of the researches adopted the H2SO4+methanol as electrolyte.
What are the roles of H2SO4 for both cases?
I don't have the correct answer but for me it's because it is a very good electrolyte, and at the same time it provides a huge density of protons in solution, you probably have to look in the equations of those two reactions, and them you will see the contribution of the sulfuric acid.
No PtOH will deposit in sulfuric acid aqueous solution.
No water oxidation when methanol oxidation in same aqueous solution.
Additionally to sergio H2SO4 is a good choice, because SO42- is electrochemically inert compared to other acid counterions like Cl-.
Yes, you need the H2SO4 electrolyte for conductivity - the water solvent alone is not very conductive. However, the SO4(2-) anion does ADsorb to electrified surfaces (specifically, positively charged surfaces as in MeOH oxidation). Sulfate isn't as strong of a "poisoning" adsorbate as the halides, but I believe perchloric acid is the preferred electrolyte because the ClO4(-) anion exerts the weakest adsorption strength on electrified Pt surfaces.
The Role of H2SO4 is, it acts as a supporting electrolyte to have a sufficient ionic conductivity. I agree with Mikes Bates sulphates poisons the Pt surface and blocks the active sites. Perchloric acid is best.
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