Dear Hadi Sharifi , I think you are seeing the effect of Liquid-Juntion potencial, that can affect the charge transfer and, in consecuence, to your cyclic voltammetry. Maybe you can fix it changing the scan rate (I see you have a cross line in your graph, that is product of a multielectron process, it is not a issue, but that indicates that you can meassure in a higher scan rate) or maybe you should use another electrolyte. I wish my answer can help you.

You have irreversible processes and adsorption of a product on electrode. Don't apply the potential higher than 1.8 V.

Without NaF, PbO2 is first electrodeposited on the surface and then reduced/desorbed from the surface. After the addition of NaF, the process is irreversible and the PbO2 is easier to adsorb on the surface. But I don't know the specific reason why NaF could facilitate the adsorption of PbO2

The complexation can be a reason for peaks shift

Dear sharifi , When you added various concentration of lead itrate in electrolyte, The current peak is consecuence raises in both case due to oxidation and reduction peak appeared. it suggest the electron transfer behavior.