Oxygen Vacancy-Tailored n-Type MXenes for Efficient Thermoelectric Energy Harvesting

MXene is an emerging 2D electronic material, which has attracted extensive attention in the fields of energy conversion and storage, electromagnetic shielding, and catalysis, etc. MXene has a wide range of types, and its abundant surface terminations and vacancy defects make it have a unique and adjustable electronic structure. Among them, oxygen vacancy (V_O) regulation is considered to be one of the most effective methods. However, it mainly relies on natural defects caused by chemical etching in preparation leading to difficult control in V_O contents. Here, an electrochemical method is proposed and successfully achieve regulation of V_O within a certain range in Ti₃C₂T_x MXene. This fact is that the V_O stems from the elimination of partial ‒OH groups. It is further confirmed that the V_O manipulation greatly increases its electrical conductivity (σ) from 1400 to 4052.3 S cm^-1, and is insensitive to Seebeck coefficient (S), resulting in a 4-folds higher thermoelectric power factor (S²σ) with good environmental stability. Systematic investigations including material structure, energy band, temperature dependence, etc., are performed to explore the V_O decoupling σ and S of V_O-Ti₃C₂T_x. This work provides a feasible strategy for the fabrication of high-performance electronic MXene, such as thermoelectric energy harvesting.