Graphene coatings for corrosion resistance of nickel and copper in acidic, alkaline and neutral environments

Graphene coatings have been reported to provide impressive corrosion resistance to nickel (Ni) and copper (Cu), because of remarkable characteristics of inertness and impermeablity of graphene. However, as the earlier investigations have generally been carried out in chloride environment, and it is important to understand the performance of graphene coating also in more aggressive environments such as acids and alkali. This study investigated the electrochemical corrosion behaviour of bare and graphene-coated (by chemical vapour deposition (CVD)) Ni and Cu in 0.5 M H₂SO₄, 0.1 M NaCl and 0.5 M NaOH solutions. Electrochemical tests and post corrosion characterisation revealed the improvement in the corrosion resistance of Ni due to multilayer graphene coating to be similar in the three solutions, i.e., the robustness of the barrier property of the multilayer graphene is largely unaffected by the aggressiveness of the corrosive environment. However, the improvement in corrosion resistance of bare Ni due to multilayer graphene is considerably greater (nearly 3 orders of magnitude) in the most aggressive of the test solutions (0.5 M H₂SO₄). The improvement is considerably less in 0.5 M NaOH because bare Ni develops a robust passive layer in highly alkaline solutions. The improvement in corrosion resistance of bare Cu is limited (within an order of magnitude) in the three solutions because Cu develops only 1–2 layers of graphene.