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This article presents a concise review of different types of inhibitors for corrosion protection on metal surfaces. Corrosion inhibitors can be of different types, which include organic, inorganic and hybrid (organic/inorganic) materials. They are also classified as cathodic, anodic and/or mixed-type inhibitors, which are based on the active inhibitor molecules that retard the corrosion process. Silicate, nitrites, molybdates, phosphates, zinc salt and cerium salt are widely used as inorganic inhibitors. Many organic compounds have been widely utilized as inhibitors. Corrosion protection will be obtained by various mechanisms such as physisorption, chemisorption, barrier protection, thin-film formation and electrochemical processes. The type of inhibitors, inhibition mechanism and the evaluation methods have been explained in detail.

In this research, poly(acrylamide) hydrogels were produced by means of free radical mechanism. Lithium acetate with different weight percentages (wt.%) such as 10 wt.%, 20 wt.%, 30 wt.%, and 40 wt.% as a source of mobile ions were incorporated into the hydrogel, and the samples were labeled as LAM1, LAM2, LAM3, and LAM4, respectively. The electrochemical impedance spectroscopy (EIS) revealed that LAM4 hydrogel electrolyte achieved the highest ionic conductivity of 9.45 × 10−3 Scm−1 with lowest activation energy (0.038 eV) at ambient temperature. The electrochemical performance of the fabricated supercapacitors using optimized LAM4 hydrogel electrolyte and different conducting substrates namely graphite foil, nickel foam, and carbon cloth was analyzed. The cyclic voltammetry and galvanic charge–discharge analyses reported that EDLC with carbon cloth resulted in maximum specific capacitance of 198.64 F g−1 at 5 mV s−1 and 439.87 F g−1 at 500 mA g−1, respectively.

Globally, researchers have devoted consistent efforts to producing excellent coating properties since coating plays an essential role in enhancing electrochemical performance and surface quality. In this study, TiO2 nanoparticles in varying concentrations of 0.5, 1, 2, and 3 wt.% were added into the acrylic-epoxy polymeric matrix with 90:10 wt.% (90A:10E) ratio incorporated with 1 wt.% graphene, to fabricate graphene/TiO2 -based nanocomposite coating systems. Furthermore, the properties of the graphene/TiO2 composites were investigated by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), ultraviolet-visible (UV-Vis) spectroscopy, water contact angle (WCA) measurements, and cross-hatch test (CHT), respectively. Moreover, the field emission scanning electron microscope (FESEM) and the electrochemical impedance spectroscopy (EIS) tests were conducted to investigate the dispersibility and anticorrosion mechanism of the coatings. The EIS was observed by determining the breakpoint frequencies over a period of 90 days. The results revealed that the TiO2 nanoparticles were successfully decorated on the graphene surface by chemical bonds, which resulted in the graphene/TiO2 nanocomposite coatings exhibiting better dispersibility within the polymeric matrix. The WCA of the graphene/TiO2 coating increased along with the ratio of TiO2 to graphene, achieving the highest CA of 120.85° for 3 wt.% of TiO2. Excellent dispersion and uniform distribution of the TiO2 nanoparticles within the polymer matrix were shown up to 2 wt.% of TiO2 inclusion. Among the coating systems, throughout the immersion time, the graphene/TiO2 (1:1) coating system exhibited the best dispersibility and high impedance modulus values (Z0.01Hz), exceeding 1010 Ωcm2.

Purpose This study aims to propose that the corrosion resistance of the neat epoxy coating can be further enhanced by incorporating reinforcing agents. Design/methodology/approach Chitosan, silica and their hybrid compound were used to study the subject of corrosion resistance of epoxy coating systems. This work used 3.5 Wt.% NaCl solution as the electrolyte, and electrochemical impedance spectroscopy (EIS) was used to investigate the electrochemical behaviour of the studied coating systems. Standard and accelerated states were used without and with scratch on the coating layer. Findings It was found that the impedance value of composite coating incorporated with the hybrid compound was significantly higher at 1010 Ω after 14 days of exposure in both testing states. The breakpoint frequency (fb) determination also proves with large capacitive region at low-to-high frequency of impedance plots corresponding to the high corrosion resistance. Originality/value The hybrid compound consisting of chitosan as organic biopolymer and silica as inorganic material, respectively, served as a promising reinforcing agent for composite coating as a promising corrosion inhibitor. Different states of EIS measurement were used which are standard (without scratch) and accelerated (with scratch) states associated with the fb values.

In this study, a co-action behavior of a hybrid composed of chitosan and silica was investigated by incorporating it into an epoxy resin to induce an active barrier effect on the metal surface. The chemical structure and porosity of the hybrid chitosan and silica were determined using Fourier-Transform Nuclear Magnetic Resonance (FT-NMR) and Brunauer–Emmett–Teller (BET), respectively. The dispersion of the hybrid chitosan/silica incorporated within the epoxy matrix was observed via Environmental Scanning Electron Microscopy (ESEM) and Fourier Transform Infrared Spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were exploited to examine the thermal stability. The wettability and degree of transparency of the hybrid composite coatings were found to be increased after being exposed to the corrosive medium and also were investigated using the contact angle (CA) measurement and ultraviolet-visible (UV–Vis) spectroscopy, respectively. CS0.8 coating has shown an increase in contact angle from 82.4 at normal condition and 89.4 and 83.6 to the exposure to NaCl solution and UV exposure respectively. The active barrier effect of the developed hybrid composite coating on mild steel surface was evaluated by the electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution to which 0.8 wt.% of hybrid chitosan/silica mass fraction exhibited pronounced impedance value up to 1010 Ω cm2 and the breakpoint frequency performed a full capacitive region even after the 60th day of exposure to the accelerated corrosive ions penetration test.

In various academic and industrial interests, graphene has achieved remarkable attention mainly by its distinctive chemical, mechanical, thermal, electrical and excellent anti-corrosion properties respectively, whereby the previous and ongoing researches have shown positive outcomes and its respective results achieved were at a satisfactory level. Over the last few years, the scope of the research on the applications of graphene based anti-corrosion has been intensely broadened and consists of two components, firstly pure graphene coatings and secondly graphene composite coatings. In the formulation of polymeric coatings, due to graphene and its derivatives having extraordinary lamellar structure, this material is highly suitable as anti-corrosive additives. Graphene creates pathways that are highly tortuous, thereby preventing the water and oxygen molecules to be diffused to the metal-based surface of materials, resulting in the protection of metal from oxidation and corrosion. Therefore, comprehensively reviewed in this article is the graphene-based coatings applications to metal anti-corrosion. First, the basic fundamentals of anti-corrosive coating technology will be discussed followed by and the current progress. Second, in detail, the preparation of graphene followed by pure graphene coatings methods respectively are illustrated. Third, the pure graphene coating in terms of corrosion resistance will be discussed, followed by detailed explanation on its existing problems and optimization respectively. Next, associated with graphene-based organic coatings, the graphene and graphene oxide dispersion and modification will be discussed, followed by the mechanism of barrier properties of graphene as well as the influence of the electrical conductivity. The anti-corrosion mechanism, optimization measures, corrosion resistance, and existing problems are summarized for the composite coatings fabricated using graphene. The challenges and future developments of anticorrosive graphene coatings are finally discussed and proposed, and their potential applications are discussed.