Multiscale and Multimodal Characterization of 2D Titanium Carbonitride MXene

A comprehensive study on the prototype solid solution phase carbonitride MXene Ti₃CN is conducted using nuclear magnetic resonance, electron spin resonance, total and quasi-elastic neutron scattering, combined with density functional theory-based electronic structure and molecular dynamic calculations. The combination of experiment and theory lead toward rational atomic structural models of Ti₃CN. The remnant Al ions from the etching process significantly tune the interlayer spacing, distinct from the more typical MXene, Ti₃C₂, prepared similarly. Neutron scattering indicates the surface terminations of Ti₃CN display high oxygen and fluorine concentrations and rather low hydroxyl and hydrogen concentrations. Calculations show that the structure including both the residual Al ions and mixed surface terminations give the best agreement with the measurements. The water molecules in Ti₃CN are highly immobile, in strong contrast to those in Ti₃C₂. The analysis of the electronic structure suggests that the nitride MXene displays higher conductivity than the carbides. The absence of hydroxyl groups in terminations, the solid-solution in the anion sites, the remnants within layers, and immobile water altogether make the carbonitrides a unique series in the MXene family, implying a further exploration of their exotic properties and applications in energy storage.