A Dual-Surface Mechanism of Oxidant-Free Pyrrole Polymerization in the Two-Dimensional Titanium Carbide (MXene) Interlayer Nanospace

The influence of confinement in acidic nanotemplates on the polymerization reaction of pyrrole was previously reported. Similarly, an in situ oxidant-free polymerization of pyrrole on and in between the Ti₃C₂ MXene layers has been demonstrated experimentally. The newly formed PPy/MXene (PPy/polypyrrole) interface showed high electrical conductivity and supercapacitor features with excellent cycling stability. However, the polymerization mechanism remains unclear. In this study, the pyrrole polymerization mechanisms on Ti₃C₂ MXene surfaces and in between MXene interlayers with different terminations were investigated based on first-principles calculations. Key factors for such oxidant-free polymerization were identified, including the configuration of surface hydrogen-bonded pyrrole, surface acidity, confinement effect, and charge transfer between MXene surfaces and pyrrole monomers. By controlling these factors, one can design covalently bonded conducting organic molecules/polymers on or in between MXene interlayers for electronic applications. These findings not only uncover the mechanism for a proton-assisted pyrrole polymerization on and in between MXene interlayers but also provide a general mechanistic understanding and guideline for other possible in situ polymerizations on and in between two-dimensional MXene interlayers.