Mxene structure: A key parameter in corrosion barrier performance of organic coatings

Surface-Modification Strategy to Produce Highly Anticorrosive Ti3C2Tx MXene-Based Polymer Composite Coatings: A Mini-Review

MXenes are a group of novel two-dimensional (2D) materials with merits such as large specific surface area, abundant surface-functional groups, high chemical activity, excellent mechanical properties, high hydrophilicity, and good compatibility with various polymers. In recent years, many novel high-performance organic anticorrosion coatings using MXenes as nanofillers have been reported and have attracted widespread attention. As the first successfully prepared MXene material, Ti3C2Tx is the most extensively studied and typical member of the MXene family. Therefore, it is taken as the representative of its family, and the status of Ti3C2Tx MXene/epoxy resin (EP) and MXene/waterborne polyurethane (WPU) polymer anticorrosive composite coatings is reviewed. Firstly, the structure, characteristics, and main synthesis methods of MXenes are briefly introduced. Then, the latest progress of four surface-modification strategies to improve the dispersion, compatibility, stability, and anti-aggregation properties of MXenes, namely functionalization grafting, orientation regulation, heterostructure nanocomposite design, and stabilization and greening treatment, are analyzed and summarized. Finally, the current challenges and future opportunities regarding MXene-based corrosion-resistant organic composite coatings are discussed prospectively.

Emerging two dimensional MXene for corrosion protection in new energy systems: Design and mechanisms

With the development of new and clean energy (offshore wind power, fuel cells, aqueous zinc ion batteries, lithium-ion batteries, etc.), the corrosion and security problems in special environments of the new energy system have attracted much attention. Corrosion protection on the metals applied in new energy system can reduce the economic loss, security risk, and energy consumption, as well as guarantee the efficiency of energy system. Traditional coatings face challenges in agglomeration of nano fillers, structural control, environmental issues, and poor conductivity, which limits the applications. With features in controllable surface chemistry and composition, rich surface terminations, better conductivity than graphene oxide, high aspect-ratio, strong impermeability, and low friction coefficient, the two-dimensional (2D) MXene presents potential for applications in corrosion protection in new energy systems. Despite progress has been made in the MXene for corrosion protection, there is still a lack of comprehensive review regarding the design and mechanisms of anti-corrosive MXene-based materials for corrosion protection in new energy system. In this review, a brief induction of MXene and the specially four corrosive environments (offshore wind power at deep sea, bipolar plates in PEMFC environments, zinc anode in AZIBs, and current collectors in Li-ion battery) are presented. Importantly, the design strategies and mechanisms of the MXene-based anti-corrosive coatings on metals used in the special environments are discussed in detail. Finally, the challenges and research trends in the MXene-based coatings for new energy systems are prospected. This review provides further understanding of corrosion in new energy and would expand the application prospects of MXene.

HD-SiO2/SiO2 Sol@PDMS Superhydrophobic Coating with Good Durability and Anti-Corrosion for Protection of Al Sheets

Superhydrophobic coatings with excellent water-repellent properties imply a wide range of application areas. However, improvements are needed in terms of stability and complex processing procedures. In the present study, a superhydrophobic coating on Al sheets was prepared by mixing hexadecyltrimethoxysilane (HDTMS)-modified SiO₂ nanoparticles and acid-catalyzed silica sols (HD-SiO₂/SiO₂ Sol) with polydimethylsiloxane (PDMS) binder. The HD-SiO₂ nanoparticles and acid-catalyzed silica sol (SiO₂ sol) form a binary graded micro-nanostructure, providing excellent superhydrophobicity (Water Contact Angle = 158.5°, Sliding angle = 0°). Superhydrophobic coatings with excellent water-repellent properties have potential for corrosion prevention. However the commonly used organic resins have poor chemical and mechanical properties. In the present study, the results of outdoor exposure for 30 days, immersion in acid and alkaline solutions for 24 h, grit abrasion, and water impact experiments, respectively, showed that the prepared superhydrophobic coating has good wear resistance. The integrated superhydrophobic coating on the Al sheets exhibited good corrosion inhibition with an efficiency (η) of 98.9%, which is much higher than that of the uncoated sheets. The present study provides a promising approach for producing stable superhydrophobic coatings at a low cost, with the potential to supplant conventional organic resin anti-corrosion coatings.

GO-functionalized MXene towards superior anti-corrosion coating

MXene flakes shows the great potential in corrosion protection area owing to their lamellar structure and remarkable mechanical features. However, these flakes are highly susceptible to oxidation, which results in their structure degradation and restrict their application in anti-corrosion field. Herein, graphene oxide (GO) was used to functionalize Ti₃C₂T_x MXene through TiOC bonding to fabricate GO-Ti₃C₂T_x nanosheets, which proved by Raman, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). GO-Ti₃C₂T_x nanosheet inclusion into the epoxy coating and their corrosion performance in 3.5 wt.% NaCl solution with 5 MPa pressure was evaluated through electrochemical techniques including open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) along with salt spray. Results indicated that GO-Ti₃C₂T_x/EP presented superior anti-corrosion capability, the impedance modulus at low frequency (|Z|_{0.01 Hz}) was above 10⁸ Ω cm² after 8 days' immersion in 5 MPa environment, which was 2 orders of magnitude higher than that of the pure epoxy coating. Scanning electron microscope (SEM) and salt spray images demonstrated that the epoxy coating loaded with GO-Ti₃C₂T_x nanosheet could provide robust corrosion protection for Q235 steel via the physical barrier effect.

Superior Anticorrosion Performance of Well-Dispersed MXene-Polymer Composite Coatings Enabled by Covalent Modification and Ambient Electron-Beam Curing

MXene-reinforced composite coatings have recently shown promise for metal anticorrosion due to their large aspect ratio and antipermeability; however, the challenges of the poor dispersion, oxidation, and sedimentation of MXene nanofillers in a resin matrix that are often encountered in the existing curing methods have greatly limited practical applications. Herein, we reported an efficient, ambient, and solvent-free electron beam (EB) curing technology to fabricate PDMS@MXene filled acrylate-polyurethane (APU) coatings for anticorrosion of 2024 Al alloy, a common aerospace structural material. We showed that the dispersion of MXene nanoflakes modified by PDMS-OH was dramatically improved in EB-cured resin and enhanced the water resistance through the additional water-repellent groups of PDMS-OH. Moreover, the controllable irradiation-induced polymerization enabled a unique high-density cross-linked network, presenting a large physical barrier against corrosive media. The newly developed APU-PDMS@MX1 coatings achieved excellent corrosion-resistance with the highest protection efficiency of 99.9957%. The coating filled with uniformly distributed PDMS@MXene promoted the corrosion potential, corrosion current density, and corrosion rate to be -0.14 V, 1.49 × 10-9 A/cm2, and 0.0004 mm/year, respectively, and the impedance modulus was increased by 1-2 orders of magnitude compared to that of APU-PDMS coating. This work combining 2D material with EB curing technology broadens the avenue for designing and fabricating composite coatings for metal corrosion protection.

Experimental and Theoretical Studies toward Superior Anti-corrosive Nanocomposite Coatings of Aminosilane Wrapped Layer-by-Layer Graphene Oxide@MXene/Waterborne Epoxy

Herein, layer-by-layer MXene/graphene oxide nanosheets wrapped with 3-aminopropyltriethoxy silane (abbreviated as F-GO@MXene) are proposed as an anti-corrosion promoter for waterborne epoxies. The GO@MXene nanohybrid is synthesized by a solvothermal reaction to produce a multi-layered 2D structure without defects. Then, the GO@MXene is modified by silane wrapping under a reflux reaction, in order to achieve chemical stability and to create active sites on the nanohybrid surface for reaction with the polymer matrix of the coating. The organic coating modified with 0.1 wt % F-GO@MXene has revealed superior corrosion protection efficiency than the organic coatings modified with either F-GO or F-MXene nanosheets. The impedance modulus at low frequency for the pure epoxy, epoxy/F-MXene, epoxy/F-GO, and epoxy/F-GO@MXene coatings is 4.17 × 10⁵, 5.5 × 10⁸, 4.46 × 10⁸, and 1.14 × 10¹⁰ Ω·cm² after 30 days of immersion in the corrosive media, respectively. The remarkable anti-corrosion property is assigned to the intense effect of the nanohybrid on the barrier performance, surface roughness, and adhesion strength of the epoxy coating. The complemental analysis based on first-principles density functional theory reveals that the adhesion strength related to the silane functional groups in its complexes follows the order F-GO@MXene > F-MXene > F-GO. The enhanced stabilization predicted on the GO@MXene nanohybrid ultimately stems from the combined role of the electrostatic and van der Waals forces, suggesting an increase in the penetration path of the corrosive media.