Controlling hydrogen environment and cooling during CVD graphene growth on nickel for improved corrosion resistance

Lack of uniformity and generation of defects including grain boundaries and wrinkles in graphene coatings synthesized using chemical vapour deposition (CVD) adversely affect the durability of these coatings. In order to control the defect density and to improve the durability of corrosion resistance of the resultant graphene coating, a fundamental understanding of the influence of the CVD parameters on the defect density is of utmost importance. In this study, the influences of hydrogen flow during graphene growth and the cooling rate on the defect density and barrier properties of a graphene coating have been investigated. A thorough microscopic and spectroscopic investigation revealed that (i) slow cooling hindered the formation of graphene coating irrespective of the presence or absence of hydrogen flow, and (ii) under rapid cooling condition, absence of hydrogen flow restricted wrinkle formation on the resultant coating. Diminished wrinkle formation in absence of hydrogen flow significantly improved the durability of the resultant coating. Based on an in-depth electrochemical impedance spectroscopic investigation, a mechanism has been proposed, which was further corroborated with the post-corrosion analyses using X-ray photoelectron spectroscopy and scanning electron microscopy. This study provides a new direction to achieve graphene coatings with minimal defect density and excellent barrier properties. (C) 2017 Elsevier Ltd. All rights reserved.