Free-standing p-Type SWCNT/MXene composite films with low thermal conductivity and enhanced thermoelectric performance

• SWCNT/MXene composites were prepared as potent p-type thermoelectric materials. • The trade-off between electrical conductivity and Seebeck coefficient was relieved. • The formed 3D hollow structure decreased the thermal conductivity greatly. • The ZT value of SWCNT/MXene-10 is 20 times higher than that of the neat SWCNTs. Single-walled carbon nanotubes (SWCNTs) show great potential as flexible thermoelectric (TE) materials, however, the low Seebeck coefficients and high thermal conductivities restrict their applications in this field. In this work, taking the advantages of one-dimensional (1D) SWCNTs and two-dimensional (2D) MXenes, a series of three-dimensional (3D) hollow structured SWCNT/MXene films had been prepared for the first time as potent p-Type TE materials. First, compared to that of SWCNTs, the Seebeck coefficients of the composites can be increased due to energy-filtering effect at the SWCNT/MXene interfaces. Holes in the SWCNTs were compensated by electrons from MXenes, leading to a decreased hole concentration, which can also increase the Seebeck coefficients. Second, 3D hollow structures were formed in the composite films, which can decrease the thermal conductivity significantly. Third, contact junctions between SWCNTs and MXenes were formed in the composites, which were beneficial for electron transfer. As a result, at MXene loading of 10 wt%, SWCNT/MXene-10 displayed the highest TE performance. The Seebeck coefficient and ZT value is about 2 times and 20 times higher than that of the neat SWCNTs, respectively. At last, a TE device consists of 10 SWCNT/MXene-10 legs was prepared with a maximum output power of 1.54 µW at temperature difference of 117.3 K. This work provides a facile strategy in designing of SWCNT-based TE materials with high performances.