My professor and I were using sulfuric acid and perchloric acid with 0.2M concentration to study the quartz crystal by EQCM technique, but we could not see any changes in mass when we increased or decreased the concentration. The mass changes data did not show any relations to the concentration changes. We were thinking about the other acids such as perbromic acid or periodic acid.
OK, what would happen, you think? QCM measures the change in the mass of the electrode. Is it a gold electrode? In an acidic solution, you will get hydrogen evolution at cathodic potentials, and the possibly adsorbed hydrogen atoms won't change the mass practically at all. At anodic potentials oxygen is evolved. There is no mass change. If you have a dissipative QCM you can possibly see the change of the viscosity of the solution if the solutions are very concentrated.
My professor and I follow this experiment design with carbon electrode and quartz crystal gold working electrode in sulfuric soltuion. The nitrogen gas was purging inside the solution before the electrochemical process. Our data showed that there was 16ng difference on the quartz crystal, but the studies could not go further when we change the concentration of sulfuric soltuion below or above 0.2M. The mass change was still around 16ng, and we assumed from the reference that the oxygen layer was adsorped on the quartz crystal surface.
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