Achieving Superior Thermoelectric Performance in Methoxy-Functionalized MXenes: The Role of Organic Functionalization

Thermoelectric technology enables the direct and reversible conversion of heat into electrical energy without air pollution. Herein, the stability, electronic structure, and thermoelectric properties of methoxy-functionalized M₂C(OMe)₂ (M = Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, and W) were systematically investigated using first-principles calculations and semiclassical Boltzmann transport theory. All MXenes, except those with M = Cr, Mo, and W, can be synthesized by substituting Cl- and Br-functionalized MXenes with deprotonated methanol, with stability governed by the M-O bond strength. Notably, semiconductors Sc₂C(OMe)₂ and Y₂C(OMe)₂ exhibit exceptionally high peak ZT values of 15.02 and 12.11 under n-type doping at 900 K, achieving a remarkable thermoelectric conversion efficiency of 53% at a temperature difference of 600 K, outperforming current high-performance thermoelectric materials. This superior performance is attributed to the weak electron-withdrawing nature of the methoxy group, which enhances nonbonding d electrons, combined with flat and degenerate band edges, and strong coupling between acoustic and optical phonons. Together, these features sustain a high Seebeck coefficient, improve electrical conductivity, and suppress lattice thermal conductivity. These findings present an effective organic functionalization strategy for designing high-performance MXenes for industrial applications and offer valuable insights for developing next-generation thermoelectric materials.