Wearable Thermoelectric Devices Based on Au-Decorated Two-Dimensional MoS2.

Two-dimensional (2D) materials have recently opened a new avenue to flexible thermoelectric materials with enhanced performance because of their unique electronic transport properties. Here, we report a feasible approach to improve the thermoelectric performance of transition-metal dichalcogenides by effectively decorating 2D MoS2 with Au nanoparticles using in situ growth. The present Au-decorated MoS2-assembled heterojunction system shows a certain decoupled phenomenon, that is, the Seebeck coefficient and conductivity increased simultaneously. This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. The composite flexible films can achieve a power factor value of 166.3 µW m-1 K-2 at room temperature, which have great potential for harvesting human body heat.

Ultrathin, Washable, and Large-Area Graphene Papers for Personal Thermal Management.

Freestanding, flexible/foldable, and wearable bifuctional ultrathin graphene paper for heating and cooling is fabricated as an active material in personal thermal management (PTM). The promising electrical conductivity grants the superior Joule heating for extra warmth of 42 °C using a low supply voltage around 3.2 V. Besides, based on its high out-of-plane thermal conductivity, the graphene paper provides passive cooling via thermal transmission from the human body to the environment within 7 s. The cooling effect of graphene paper is superior compared with that of the normal cotton fiber, and this advantage will become more prominent with the increased thickness difference. The present bifunctional graphene paper possesses high durability against bending cycles over 500 times and wash time over 1500 min, suggesting its great potential in wearable PTM.

Self-Assembled Heterostructures: Selective Growth of Metallic Nanoparticles on V2 -VI3 Nanoplates.

Precise control of the selective growth of heterostructures with specific composition and functionalities is an emerging and extremely challenging topic. Here, the first investigation of the difference in binding energy between a series of metal-semiconductor heterostructures based on layered V2 -VI3 nanostructures is investigated by means of density functional theory. All lateral configurations show lower formation energy compared with that of the vertical ones, implying the selective growth of metal nanoparticles. The simulation results are supported by the successful fabrication of self-assembled Ag/Cu-nanoparticle-decorated p-type Sb2 Te3 and n-type Bi2 Te3 nanoplates at their lateral sites through a solution reaction. The detailed nucleation-growth kinetics are well studied with controllable reaction times and precursor concentrations. Accompanied by the preserved topological structure integrity and electron transfer on the semiconductor host, exceptional properties such as dramatically increased electrical conductivity are observed thanks to the pre-energy-filtering effect before carrier injection. A zigzag thermoelectric generator is built using Cu/Ag-decorated Sb2 Te3 and Bi2 Te3 as p-n legs to utilize the temperature gradient in the vertical direction. Synthetic approaches using similar chalcogenide nanoplates as building blocks, as well as careful control of the dopant metallic nanoparticles or semiconductors, are believed to be broadly applicable to other heterostructures with novel applications.

2D Chalcogenide Nanoplate Assemblies for Thermoelectric Applications.

Engineered atomic dislocations have been used to create a novel, Sb2 Te3 nanoplate-like architecture that exhibits a unique antisymmetric chirality. High-resolution transmission electron microscopy (HRTEM) coupled with atomic force microscopy and X-ray photoelectron spectroscopy reveals the architectures to be extremely well ordered with little residual strain. Surface modification of these topologically complex macrostructures (≈3 µm) has been achieved by direct growth of metallic Ag nanoparticles onto the edge sites of the Sb2 Te3 . Again, HRTEM shows this nanoparticle decoration to be atomically sharp at the boundaries and regularly spaced along the selvedge of the nanostructure. Transport experiments of densified films of these assemblies exhibit marked increases in carrier density after nanoengineering, yielding 3.5 × 104 S m-1 in electrical conductivity. An increased Seebeck coefficient by 20% in parallel with electrical conductivity is also observed. This gives a thermoelectric power factor of 371 µW m-1 K-2 , which is the highest value for a flexible, freestanding film to date. These results suggest an entirely new direction in the search for wearable power harvesters based on topologically complex, low-dimensional nanoassemblies.

Layered Bi2Se3 nanoplate/polyvinylidene fluoride composite based n-type thermoelectric fabrics.

In this study, we report the fabrication of n-type flexible thermoelectric fabrics using layered Bi2Se3 nanoplate/polyvinylidene fluoride (PVDF) composites as the thermoelectric material. These composites exhibit room temperature Seebeck coefficient and electrical conductivity values of -80 µV K(-1) and 5100 S m(-1), respectively, resulting in a power factor approaching 30 µW m(-1)K(-2). The temperature-dependent thermoelectric properties reveal that the composites exhibit metallic-like electrical conductivity, whereas the thermoelectric power is characterized by a heterogeneous model. These composites have the potential to be used in atypical applications for thermoelectrics, where lightweight and flexible materials would be beneficial. Indeed, bending tests revealed excellent durability of the thermoelectric fabrics. We anticipate that this work may guide the way for fabricating high performance thermoelectric fabrics based on layered V-VI nanoplates.

Flexible thermoelectric fabrics based on self-assembled tellurium nanorods with a large power factor.

Highly-flexible thermoelectric fabrics were fabricated based on a layered structure, composed of a thin active layer of self-assembled tellurium nanorods and a substrate layer of polyvinylidene fluoride. The resulting thermoelectric fabrics show a high room temperature power factor of 45.8 µW m(-1) K(-2), which opens a new avenue to fabricate highly-flexible sustainable energy sources.

Multilayered carbon nanotube/polymer composite based thermoelectric fabrics.

Thermoelectrics are materials capable of the solid-state conversion between thermal and electrical energy. Carbon nanotube/polymer composite thin films are known to exhibit thermoelectric effects, however, have a low figure of merit (ZT) of 0.02. In this work, we demonstrate individual composite films of multiwalled carbon nanotubes (MWNT)/polyvinylidene fluoride (PVDF) that are layered into multiple element modules that resemble a felt fabric. The thermoelectric voltage generated by these fabrics is the sum of contributions from each layer, resulting in increased power output. Since these fabrics have the potential to be cheaper, lighter, and more easily processed than the commonly used thermoelectric bismuth telluride, the overall performance of the fabric shows promise as a realistic alternative in a number of applications such as portable lightweight electronics.