Construction of an inorganic/organic superlattice-based film has been proven effective in enhancing thermoelectric (TE) performance as well as flexibility by a variety of mechanisms, typically for two-dimensional (2D) TiS2-based flexible TEs. MXenes, typically, Ti3C2T x , are a type of 2D material widely investigated in fields of flexible batteries and electromagnetic shielding, among others. However, they have rarely been reported in flexible TEs. One of the key factors is that the surface termination groups (−T) on an MXene could trap electrons, restricting the electronic transport. Herein, −T groups were tailored and substituted by organic ions (−HA) by facile preannealing, exfoliation, and reassembly. The intercalation of −HA introduced Ti–N bonding, forming a flexible MXene/organic superlattice film. The electrical conductivity of the superlattice film was increased by 5 times to 1.6 × 105 S m–1 due to defect reduction as well as the electron injection effect. While the Seebeck coefficient was maintained, the power factor was increased from 4 to 18 μW m–1 K–2. The TE module based on the superlattice film revealed an output power of 7.6 nW at a temperature gap of 50 K. This work opens up an avenue of fabricating flexible MXene-based TE films by tailoring the surface termination group and constructing inorganic/organic superlattice structures.

The flexible thermoelectric (TE) generator has emerged as a superior alternative to traditional batteries for powering wearable electronic devices, as it can efficiently convert skin heat into electricity without any safety concerns. MXene, a highly researched twodimensional material, is known for its exceptional flexibility, hydrophilicity, metallic conductivity, and processability, among other properties, making it a versatile material for a wide range of applications, including supercapacitors, electromagnetic shielding, and sensors. However, the low intrinsic Seebeck coefficient of MXene due to its metallic conducting nature poses a significant challenge to its TE application. Therefore, improving the Seebeck coefficient remains a primary concern. In this regard, a flexible MXene/organics/TiS 2 misfit film was synthesized in this work through organic intercalation, exfoliation, and re-assembly techniques. The absolute value of Seebeck coefficient of the misfit film was significantly enhanced to 44.8 μV K −1 , which is five times higher than that of the original MXene film. This enhancement is attributed primarily to the weighted effect of the Seebeck coefficient and possibly to energy-filtering effects at the heterogeneous interfaces. Additionally, the power factor of the misfit film was considerably improved to 77.2 μW m −1 K −2 , which is 18 times higher than that of the original MXene film. The maximum output power of the TE device constructed of the misfit film was 95 nW at a temperature difference of 40 K, resulting in a power density of 1.18 W m −2 , demonstrating the significant potential of this technology for driving low-energy consumption wearable electronics.

Thermoelectric (TE) generators are a kind of clean energy technology that can harvest electrical energy from waste heat. However, scant attention has been paid to the potential influence of the bonding orbitals on TE properties, which has severely hindered the exploitation of TE materials. Herein, a simple but effective strategy based on crystal field theory was proposed here to sift out potential TE materials based on the orbital degeneracy engineering that comprises the electronic bands. A typical p-type material Cu 8 SiS 6 composed of CuS 4 tetrahedra−units was selected and investigated. When the ligands−sulfur atoms get close to the center copper ion in a unit CuS 4 , the degeneracy of the d orbital would split due to the static electric field, leading to a high density of state at the top of the valence band, thus enhancing the Seebeck coefficient. It was found that Cu 7.92 SiS 6 shows a zT of 0.24 at 850 K. The orbital degeneracy engineering approach is promising to extend to other class of TE materials, thereby substantially accelerating the screening and design of novel TE materials.

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