Electron localization in Janus structure enhances phonon thermal transport in M2C (M = V, Nb, Ta) MXene

Despite Janus materials showing great potential for thermal conductivity tuning, the mechanisms remain poorly understood, as structural asymmetry challenges conventional symmetric theories. Here, we investigate thermal transport in monolayer M2C (M = V, Nb, Ta) MXenes and Janus MʹVC (Mʹ = Nb, Ta), revealing how electron localization enhances phonon thermal transport in Janus structures. In the M2C series, Nb2C has slightly lower thermal conductivity (κ) than V2C, while Ta2C shows an anomalous increase. However, Janus NbVC and TaVC exhibit far higher κ than pristine MXenes. Electronic analysis shows Ta/Nb d-orbital localization lies between C and V. Electron repulsion around Ta strengthens atomic restoring forces, weakening phonon anharmonicity. V delocalization in Janus structures further enhances this effect, prolonging phonon relaxation times and boosting κ. This enhancement originates from reduced phonon anharmonicity regulated by electron localization through interatomic interactions. This work provides theoretical support for the application of Janus MʹVC in thermal management.