Excellent corrosion resistance of graphene coating on copper due to the low defect overlapping structure

Nowadays, ultra-thin graphene coating can provide considerable resistance against corrosion for various metals, however, there is great variability and contradictory in corrosion resistance mechanism of graphene coating reported in different studies. In this work, the anti-corrosion behaviors of graphene coatings with different defect values on the copper surface were investigated systematically. The results indicated that all graphene coated Cu exhibited superior corrosion resistance than heat treated Cu, regardless of the layer number of graphene. Particularly, anti-corrosion performance of bi-layer graphene coating with the low defect density was the most effective, the corrosive medium transferred a long way to reach the interface between Cu and graphene. The corrosion resistance for mono-layer graphene was inferior to bi-layer graphene, caused by the direct corrosion at the defect site and the galvanic corrosion between copper and graphene. Poor corrosion resistance for multi-layer graphene was due to the high value of defects increasing the corrosion pathways, which leads to easier transfer for the chloride ions among defects. Consequently, the corrosion resistance ability of graphene coatings was mainly determined by the defect density other than the layer number, multi-layer graphene coating may not behave better anti-corrosion performance if it contained a high value of defect.