Enhancement of thermoelectric transport in surface halogenated Ti2O MOenes via electron–phonon drag effect

Designing efficient and environmentally friendly thermoelectric materials near room temperature is critical, and the electron–phonon drag effect on thermoelectric transport in monolayers remains largely unexplored. This manuscript systematically investigates the electron–phonon drag effect in surface halogenated Ti₂O MOenes (Ti₂OX₂, X = F, Cl) by solving fully coupled electron–phonon Boltzmann transport equations. We find that the phonon drag effect significantly enhances the total Seebeck coefficient and various electronic transport coefficients, including the thermal response of electrons to an electric field, electrical conductivity, and electronic thermal conductivity at zero field, while the electron drag effect notably increases the lattice thermal conductivity, especially at high carrier concentrations and low temperatures. Furthermore, the electron–phonon drag effect significantly increases the thermoelectric figure of merit (zT) across 100–900 K, with the greatest enhancement at low temperatures. At room temperature, zT increases by 13.73 times for Ti₂OF₂ and 2.82 times for Ti₂OCl₂, achieving maximum values of 0.92 and 0.84, respectively. Our work underscores the superior thermoelectric performance of surface halogenated Ti₂O MOenes near room temperature and the potential of leveraging electron–phonon drag effects to enhance the electrical, thermal and thermoelectric transport in monolayers.