Graphene coating on nickel as effective barriers against hydrogen embrittlement

Hydrogen embrittlement (HE) is a significant problem for many metal alloys leading to the degradation of mechanical strength and lifetime. Here we report that a graphene coating deposited by chemical vapor deposition can effectively protect nickel against hydrogen embrittlement. We find the degree of protection depends strongly on the graphene synthesis condition. Using ethanol as the carbon feedstock and a high cooling rate are essential in achieving effective protection. To reveal the mechanism, hydrogen permeation tests are performed, and the permeation current analyzed on different samples. Additional characterization such as optical transmission, Raman spectroscopy, and mechanical strength tests are also performed on the graphene coating. We propose that hydrogen permeates graphene in two alternating steps - transport through in-plane defects and intercalation which expands the interlayer spacing. This work demonstrates that graphene is an effective coating against HE and points out the direction to further improve the protection effectiveness.