While doing some electrochemical sensing experiments for amino acid, I noticed that my nanomaterial exhibiting oxidation peak around 0.4V, whereas all previous reports showing its oxidation potential around 0.7-0.9V.
I checked and found out that in my case, overpotential has been reduced considerably.
Make sure you are doing right comparison, oxidation potential also depends on pH, the type of reference electrode used and molarity of electrolyte used in ref electrode. I'm using nanoparticles for chemical sensing, whenever I change electrolyte their oxidation peak slightly changes.
I think your material is not showing any peak at all. Oxidation peak at 0.4 might be due to oxygen, have you degased your system (by perging nitrogen gas) ? If after this peak at 0.4 vanished you'll be sure of reason, and you can redesign your material/system.