MXenes are attracting ever growing attention for applications in energy storage, electromagnetic interference (EMI) shielding, superconductivity, and catalysis. Traditional preparation of MXenes involves high-temperature synthesis the MAX phase followed by its chemical etching and exfoliation. This synthetic route has high energy consumption, poor atom economy, and uses large amounts of hazardous HF or Lewis acidic molten salts. The development of fast, facile, and atom-economic synthetic methods would greatly facilitate widespread practical applications of the rapidly developing family of functional MXenes. An ideal approach would involve direct interconversion of inexpensive precursors into MXenes bypassing intermediate MAX phases.
Here we report direct synthesis of Ti₂CCl₂ MXene. The reaction is easily scalable, inexpensive, energy efficient, and more environmentally friendly compared to the traditional route. The directly synthesized MXene also showed excellent energy storage capacity for Li-ion intercalation. Besides convenience and scalability, the direct synthesis route offers new synthetic modalities not compatible with traditional MAX phase etching methods. Thus, we demonstrated chemical vapor deposition (CVD) synthesis of Ti₂CCl₂, Zr₂CCl₂, and Zr₂CBr₂ MXenes, producing carpets of MXene sheets oriented perpendicular to substrate. Such orientation makes MXene surface easily accessible for ion intercalation and exposes catalytically active edge sites.

Direct synthesis of MXene

CVD of MXene

Wooje Cho

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