AbstractWith the growing interest in low dimensional materials, MXenes have also attracted considerable attention recently. In this work, the thermal and electrical properties of oxygen-functionalized M₂CO₂ (M = Ti, Zr, Hf) MXenes are investigated using first-principles calculations. Hf₂CO₂ is determined to exhibit a thermal conductivity better than MoS₂ and phosphorene. The room-temperature thermal conductivity along the armchair direction is determined to be 86.25~131.2 Wm⁻¹ K⁻¹ with a flake length of 5~100 μm. The room temperature thermal expansion coefficient of Hf₂CO₂ is 6.094 × 10⁻⁶ K⁻¹, which is lower than that of most metals. Moreover, Hf₂CO₂ is determined to be a semiconductor with a band gap of 1.657 eV and to have high and anisotropic carrier mobility. At room temperature, the Hf₂CO₂ hole mobility in the armchair direction (in the zigzag direction) is determined to be as high as 13.5 × 10³ cm²V⁻¹s⁻¹ (17.6 × 10³ cm²V⁻¹s⁻¹). Thus, broader utilization of Hf₂CO₂, such as the material for nanoelectronics, is likely. The corresponding thermal and electrical properties of Ti₂CO₂ and Zr₂CO₂ are also provided. Notably, Ti₂CO₂ presents relatively lower thermal conductivity but much higher carrier mobility than Hf₂CO₂. According to the present results, the design and application of MXene based devices are expected to be promising.