Tuning the functionalization degree of graphene: Determining critical conditions for inhibiting the corrosion promotion activity of graphene/epoxy nanocomposite coatings

•Graphene with different functionalization degree is precisely prepared.•Corrosion behaviour near the defect of graphene-reinforced coating is studies by LEIS.•Critical functionalization degree for inhibiting the CPA of graphene is 5.92 at.% of Si.•Only graphene with high functionalization degree exhibits inhibited CPA.