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Printed electronics implies the use of low-cost, scalable, printing technologies to fabricate electronic devices and circuits on flexible substrates, such as paper or plastics. The development of this new electronic is currently expanding because of the emergence of the internet-of-everything. Although lot of attention has been paid to functional inks based on organic semiconductors, another class of inks is based on nanoparticles obtained from exfoliated 2D materials, such as graphene and metal sulfides. The ultimate scientific and technological challenge is to find a strategy where the exfoliated nanoparticle flakes in the inks can, after solvent evaporation, form a solid which displays performances equal to the single crystal of the 2D material. In this context, a printed layer, formed from an ink composed of nano-flakes of TiS2 intercalated with hexylamine, which displays thermoelectric properties superior to organic intercalated TiS2 single crystals, is demonstrated for the first time. The choice of the fraction of exfoliated nano-flakes appears to be a key to the forming of a new self-organized layered material by solvent evaporation. The printed layer is an efficient n-type thermoelectric material which complements the p-type printable organic semiconductors The thermoelectric power factor of the printed TiS2/hexylamine thin films reach record values of 1460 µW m−1 K−2 at 430 K, this is considerably higher than the high value of 900 µW m−1 K−2 at 300 K reported for a single crystal. A printed thermoelectric generator based on eight legs of TiS2 confirms the high-power factor values by generating a power density of 16.0 W m−2 at ΔT = 40 K. [ABSTRACT FROM AUTHOR]

Abstract: A new class of proton conducting inorganic–organic polymer (ORMOCER®) electrolytes for fuel cells based on polycondensed and organically cross-linked sulfonyl- and styrene-functionalized alkoxysilanes has been developed [1]. Different synthesis processes are used to take account of the different acidities of the starting alkoxydes. System-I is based on the separate hydrolysis and condensation of the acid and basic alkoxysilanes. Sulfonated alkoxysilanes and a styrene derivative functionalized alkoxysilane are hydrolyzed and co-condensed in parallel to the alkoxysilane containing at least a nitrogen heterocycle, an amine group or a sulfonamide group and a styrene derivative functionalized alkoxysilane. The two polycondensates are then mixed; the resulting resins are shaped into thin films and organically cross-linked via UV and/or thermal curing. Improvements of mechanical and electrochemical properties lead to System-II in which the sulfonated functionalized alkoxysilane is first hydrolyzed and condensed, then the two other alkoxysilanes are added for co-condensation. In system-III the three alkoxysilanes used for system-I are hydrolyzed and co-condensed without any partial hydrolysis of one of the components. The three systems present a good thermal stability up to 180°C. The conductivity of the materials shows an Arrhenius behavior in the temperature range 25–110°C with activation energies of 0.45 up to 0.78eV depending on sample composition. A 1.0×10−2 Scm−1-conductivity value was measured for system-II/imidazole membranes at 110°C under an inert gas atmosphere. The conductivity of anhydrous system-III/imidazole membranes goes from 9.1×10−3 Scm−1 at 100°C to 2.0×10−2 ±1.5×10−3 Scm−1 at 140°C. [Copyright &y& Elsevier]

Proton conducting inorganic–organic hybrid polymer electrolytes were developed in the last decade based on sulfonated, methacryl and epoxy functionalized alkoxysilanes for thin film cells [Electrochim. Acta 45 (2000) 137]. To improve the electrochemical stability of the materials for applications like polymer electrolyte membranes for direct methanol fuel cells, the less stable methacryl and epoxy alkoxysilanes of the former test system [Electrochim. Acta 45 (2000) 137] were replaced by styrene derivative functionalized alkoxysilanes. These alkoxysilanes were synthesized with a new modified Grignard reaction. The sol–gel materials were prepared in a two-step reaction: first, an alkoxysilane containing a sulfonated group and an alkoxysilane containing at least a nitrogen heterocycle, an amine group or a sulfonamide group were separately hydrolyzed and co-condensed each with one half of the amount of a styrene derivative functionalized alkoxysilane. Then, these two co-condensates were mixed. After evaporation of the solvent, the resin was cast in Teflon® moulds or applied on a substrate as a film and finally organically cross-linked via UV and/or thermal curing. The influence of the sample composition on the conductivity and the mechanical properties was studied. Conductivities of 3×10−3 S cm−1 at room temperature were obtained for membranes free of water, whose precursor composition consists of 60% sulfonated alkoxysilane, finally mixed with 2 mol imidazole per mol &z.sbnd;SO3H. If the imidazole is exchanged by water (max. 15 mass% absorption within membrane), the membranes show conductivities up to 8×10−3 S cm−1 at room temperature. A thermal stability of the inorganic–organic matrix of up to 180 °C (<5% weight loss) was measured by thermo-gravimetric (TG) analysis. [Copyright &y& Elsevier]

Copper sulfides and copper selenides have recently been reported as new and promising low-cost and environmentally friendly thermoelectric materials. Here, it is shown that these materials have actually been studied for more than 190 years and the absence of commercial thermoelectric modules based on them stems from some major intrinsic issues related to these chalcogenides. Further development of these semiconductors will require addressing and solving these problems before large scale utilization can be considered. [ABSTRACT FROM AUTHOR]

Electronic and transport properties of Bi2S3 with various dopants are studied using density functional theory and experimental characterizations. First, principle calculations of thermoelectric properties are used to evaluate the thermoelectric potential of the orthorhombic Bi2S3 structure. The computational screening of extrinsic defects is used to select the most favorable n-type dopants. Among all the dopants considered, hafnium and chlorine are identified as prospective dopants, whereas, e.g., germanium is found to be unfavorable. This is confirmed by experiment. Seebeck coefficient (S) and electrical conductivity (σ) measurements are performed at room temperature on pellets obtained by spark plasma sintering. An increase of power factors (S2·σ) from around 50 up to 500 μW K-2m-1 is observed for differently doped compounds. In several series of samples, we observed an optimum of power factor above 500 μW K-2m-1 at room temperature for a chlorine equivalence of 0.25 mol. % BiCl3. The obtained results are plotted on a semilogarithmic log (r) versus S graph to demonstrate that a very strong linear trend that limits the power factor around 500 μW K-2m-1 exists. Further improvement of Bi2S3 as thermoelectric material will require finding new doping modes that will break through the observed trend. The results of stability tests demonstrate that properties of optimally doped Bi2S3 are stable. [ABSTRACT FROM AUTHOR]

In order to reduce the thermal conductivity of CoSbS, a newly developed thermoelectric semiconductor, we have aimed at intentionally induce atomic disorder in its structure. This endeavor was guided by Density Functional Theory(DFT) calculations which indicated that substituting sulfur with selenium might be easily achievable experimentally because of the low formation energy of this point defect. Thereby, CoSbS1−xSex compounds having 0 ≤ x ≤ 1 have been synthesized by solid state reaction. Besides the expected semiconducting paracostibite phase, we have observed the appearance of a semimetallic costibite phase, never reported experimentally before. This cross-fertilized theoretical and experimental approach allowed us to reduce by 50% the thermal conductivity of paracostibite and therefore reach a maximum zT of 0.62 at 730 K. This makes this entirely new CoSbS1−xSex alloy very attractive for further optimizations and potential usage in thermoelectric applications. [ABSTRACT FROM AUTHOR]