Development of electrophoresed anti-corrosion coating for copper from functionalized multi layered graphene nano-sheets synthesized through anionic acidic electrochemical exfoliation

Abstract

Following the discovery of graphene, a two-dimensional carbonaceous substance, numerous possibilities in materials science domain have evolved, one being its function as a corrosion inhibitor. This investigation undertakes the synthesis of functionalized multi-layered graphene nanosheets (FMLGNs) from pyrolytic graphite sheets through electrochemical exfoliation involving four distinct acid-based solutions (H2SO4, HCLO4, HNO3 and combination of the above three in 1:1:1 ratio). Post-exfoliation analysis of FMLGNs included X-ray diffraction (XRD) wherein 2θ values were reported at 26° confirming graphene's presence. Raman spectroscopy reiterated the same observation along with an increase in ID/IG ratio to ≈ 1 hinting at the presence of functional groups and defects. UV–visible spectroscopy indicating π-π* transitions, Fourier transform infrared spectroscopy (FTIR) showing CO stretching and X-ray photoelectron spectroscopy (XPS) with a C/O ratio = 3.12 gave an idea about the functionalization in FMLGNs. Average particle sizes of FMLGNs was in the range of 400–500 nm and zeta potential measurements showed stable dispersion behaviour (≈−40 mV). Utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), authors observed a layered (10–15 layers), overlapping shape of FMLGNs. Electrophoretic deposition (EPD) method was employed to coat FMLGNs onto copper substrates under various iterative conditions (number of layers and time of deposition) which produced depositions of ≈20–30 μm. SEM images displayed adequate coverage of graphene sheets on copper surfaces, backed by energy-dispersive x-ray spectroscopy (EDS). Crack propagation resistance (CPR) values of 34.03 N highlighted better adherence than other similar coatings. The coated copper samples were subjected to cyclic voltammetry (CV), potentio-dynamic polarization (PDP) and electrochemical impedance (EIS) tests in 3.5 wt% NaCl solution for analysing the inhibitory impacts of coatings. An inhibition efficiency of 85 % and charge transfer resistance of 5535 Ω.cm2 was observed, which highlighted better corrosion mitigation than reported literatures. The authors also identified that 1 layered coatings showed better reliability than two layered coatings.