Gradient-Crosslinked MXene-Armored Microcapsules with pH-Triggered Self-Healing for Anti-Corrosion Coatings in High-Pressure CNG Storage Tanks

Abstract

We present a gradient-crosslinked MXene-armored microcapsule coating system designed to address corrosion and gas permeation challenges in high-pressure compressed natural gas storage tanks. The core innovation involves fabricating microcapsules through sequential interfacial polymerization combined with layer-by-layer assembly, producing shells with a radial crosslink density gradient. The outer shell region incorporates titanium carbide MXene nanosheets at a loading of 2.5 weight percent, which are aligned parallel to the shell surface and reduce methane permeability by a factor of approximately 7.2 according to the modified Nielsen model. This gas barrier property substantially suppresses methane ingress and moisture accumulation at the coating–liner interface under cyclic pressures reaching 35 megapascals. The inner shell compartment contains benzotriazole corrosion inhibitor at 18 weight percent loading. Furthermore, we covalently graft pH-responsive polyzwitterionic chains onto the inner shell surface, which remain collapsed at neutral pH but undergo chain extension and swelling when exposed to local alkaline environments generated by cathodic corrosion reactions. This pH-triggered behavior provides on-demand inhibitor release precisely at active corrosion sites, achieving cumulative release of eighty percent over seventy-two hours under accelerated alkaline conditions. When fatigue microcracks propagate through the coating and rupture proximal microcapsules, the released benzotriazole adsorbs onto the aluminum substrate via coordination bonding, forming a protective molecular layer that inhibits anodic dissolution. Simultaneously, oxidative polymerization of benzotriazole seals the defect, restoring barrier integrity to over ninety percent of the original electrochemical impedance within twenty-four hours. The proposed system synergistically combines MXene-induced tortuosity for gas barrier functionality with stimuli-responsive self-healing, thereby providing autonomous corrosion prevention under the demanding cyclic mechanical loads and high-pressure methane environment of compressed natural gas storage.

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