Development of Anti-Corrosion Coatings for Copper from Electrochemically Exfoliated Few Layered Graphene Nano-Sheets

Abstract

“Corrosion” is an age-old phenomenon that has crucially affected humanity especially the industrial sector causing substantial economic losses and also compromising safety. In order to counteract this “destructive” force, many mechanisms have been developed out of which “coatings” are a reliable method. Deposition of graphene on copper has found use in electronics, energy storage, and catalysis, among other fields due to the outstanding properties of graphene coupled with copper's strong thermal and electrical conductivity. The current work revolves around the idea of using graphene as a corrosion preventor owing to its exceptional mechanical, electrical, and barrier properties. The concept of electrophoretic deposition has been utilized to coat graphene nanosheets onto copper substrates and the latter has been tested for corrosion preventive behaviour. In present study, few layer graphene nanosheets (FLGNs) were synthesized from pyrolytic graphite by using four different molarities of Na2SO4 (sodium sulphate) aqueous solution in concentrations of 0.5 M, 1.0 M, 1.5 M and 2.0 M via electrochemical exfoliation methodology. FLGNs were also exfoliated from four different acid-based solutions of 1 M concentration (sulphuric, perchloric, nitric and combination of the three). The obtained FLGNs were characterised by XRD spectroscopy, Raman spectroscopy, UV spectroscopy, FTIR spectroscopy, XPS spectroscopy, DLS, SEM, TEM and AFM. X-ray diffraction and Raman is used to investigate structural characteristics and crystal structure arrangement. (002) lattice plane corresponding to basal plane of graphene is identified at around 26° (2θ angle). Raman spectroscopy depicts an increase in disordered value of the FLGNs which may be due to exfoliative activity and surface functionalization. UV, FTIR and XPS confirm the presence of functional groups attached to graphene network which however was not present in large amounts in the case of FLGNs derived from Na2SO4 solutions. Acid based FLGNs on the other hand showed a higher oxygen content pointing out to the presence of hydroxyl and carbonyl groups. The energy transitions occurring with respect to π-π* and n-π* orbitals are detected through the absorbance spectra in UV-visible spectroscopy. A wrinkled, folded sheet type of structure is visible in SEM which appears arranged in a stacked manner. TEM depicts transparent and semi-transparent morphologies which gives idea about the number of layers. AFM supplements the morphological results by giving inputs about the lateral dimensions and approximate number of layers. The obtained FLGNs were dispersed in double distilled water and ultrasonicated for around 3 – 4 hours to get a homogenous solution. This solution is then used for electrophoretic deposition with copper substrates as anode and graphite rod as cathode. The samples are coated through a iterative process consisting of different potentials, time and layers. A set of coatings was made to undergo heat treatment (130°C for 1 hour) to analyse the effects. Methyl violet (surfactant) was dispersed with graphene for creating another set of coatings to view the effects of added environment. The coatings were observed under optical microscope and SEM for morphological characterization along with EDS. SEM micrographs show layer-upon-layer deposition of graphene on copper substrate. The coatings were subjected to scratch tests to determine their adhesion strength and complement the electrochemical measurements. Thereafter, the coatings underwent potentiodynamic polarization and electrochemical impedance spectroscopy tests to assess their corrosion characteristics and coating behaviour. Results from polarisation and impedance testing demonstrated that graphene was an effective corrosion barrier compared to an uncoated substrate. The authors also made an effort to comprehend how the coating's thickness impacts the substrate and the latter's resistance to damage. It was discovered that 2-layer coatings provided the best resistance. In conclusion, graphene's use for corrosion protection seems warranted, however further research is obviously necessary.