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• The 2H phase W 2 C and W 2 CO 2 are more stable MXenes than their 1T phase. • Oxygen functionalization increases the thermal conductivity of 2H phase W 2 C. • The 2H phase W 2 CO 2 has high Young's modulus up to 351 N m−1. • Spin-orbit coupling causes a metallic-semiconducting transition of 2H phase W 2 CO 2. MXenes, which are different from the 1T phase, have attracted increasing researches due to their unique physical and chemical properties. In this paper, we investigated the structure stabilities, lattice dynamics, mechanical properties and electronic structures of 2H phase W 2 C monolayer. Similar to the traditional 1T phase, functionalization also has a significant effect on these properties of 2H phase W 2 C. The O-functionalization improves the structural stability, thermal conductivity and mechanical properties. In particular, the Young's modulus of 2H phase W 2 C can be raised to 351 N m−1 after O-functionalized, which is higher than that of graphene. The electronic structures show that there is a metallic-semiconducting transition after O-functionalization when considering spin-orbit coupling effect. 2H phase W 2 CO 2 has semiconductor character with 0.199 eV band gap and a large spin splitting. We hope that our results can further contribute to the development of 2H phase MXenes in experimental synthesis and potential applications. [ABSTRACT FROM AUTHOR]