Fabrication of porous SnSeS nanosheets with controlled porosity and their enhanced thermoelectric performance

Ju, Hyun,Kim, Kiho,Park, Dabin,Kim, Jooheon Elsevier 2018 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.335 No.-

<P><B>Abstract</B></P> <P>IV–VI-group Sn–chalcogenide-based nanomaterials have attracted interest in various research fields because they offer unique characteristics distinct from their bulk counterparts. The introduction of pores can manipulate the electrical and thermal transport characteristics of the material, which is considered a promising strategy to improve the thermoelectric properties. Herein, we report on the successful fabrication and optimization of porous SnSeS-based nanosheets and their thermoelectric enhancement. Two-dimensional SnSe<SUB>0.8</SUB>S<SUB>0.2</SUB> (SnSeS) nanocrystals are chemically exfoliated from a layered bulk structure through a Li-intercalation and exfoliation process. Many pores are successfully introduced to the SnSeS nanosheets by solution-phase chemical transformation, and the porosity of the materials is optimized by manipulating the reaction time, resulting in the effective reduction of the thermal conductivity and enhancement of the thermoelectric performance. The incorporation of nanoscale and porous structure can accelerate research advances regarding nanoscale porous materials and high-performance thermoelectrics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SnSeS nanosheets are prepared from bulk via a Li-intercalation and exfoliation. </LI> <LI> A lot of pores are introduced into the nanosheets through a chemical transformation. </LI> <LI> Porosity of SnSeS nanosheet is engineered by manipulating reaction time. </LI> <LI> Low thermal conductivity leads to the outstanding thermoelectric performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

The effect of temperature on thermoelectric properties of n-type Bi₂Te₃ nanowire/graphene layer-by-layer hybrid composites

Ju, Hyun,Kim, Jooheon The Royal Society of Chemistry 2015 Dalton transactions Vol.44 No.26

<P>The thermoelectric properties of Bi<SUB>2</SUB>Te<SUB>3</SUB> nanowire/graphene composites prepared at different sintering temperatures have been investigated. The as-synthesized ultrathin Bi<SUB>2</SUB>Te<SUB>3</SUB> nanowires are uniformly distributed between the graphene layers, leading to the formation of Bi<SUB>2</SUB>Te<SUB>3</SUB> nanowire/graphene layer-by-layer hybrid structures. The electrical conductivity of the as-sintered composites increases dramatically with the sintering temperature, as the relative density and grain size increase and the interface density decreases. This in turn lowers the Seebeck coefficient due to the reduction of the potential barrier for carriers and their scattering at the interface. The fabricated n-type Bi<SUB>2</SUB>Te<SUB>3</SUB> nanowire/graphene composites exhibit an enhanced figure of merit of 0.25 at an optimal sintering temperature of 623 K.</P> <P>Graphic Abstract</P><P>The thermoelectric properties of Bi<SUB>2</SUB>Te<SUB>3</SUB> nanowire/graphene composites prepared at different sintering temperatures have been investigated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5dt00897b'> </P>

Synthesis and Antibacterial Activity of Novel Cephalosporins Containing 2,3-Disubstituted-1,8-naphthyridiniummethyl Group at the C-3 Position

Ju, Hyun,Im, Sun-Kwon,Jeon, Jae-Man,Kang, Jae-Seon,Kim, Dong-Uk,Cho, Sung-Ki Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.11

Fabrication of conductive polymer/inorganic nanoparticles composite films: PEDOT:PSS with exfoliated tin selenide nanosheets for polymer-based thermoelectric devices

Ju, Hyun,Kim, Jooheon Elsevier 2016 Chemical engineering journal Vol.297 No.-

<P><B>Abstract</B></P> <P>Organic polymer based thermoelectric films consisting of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with inorganic tin selenide (SnSe) nanosheets were fabricated. Two-dimensional SnSe nanosheets were prepared by Li intercalation and subsequent exfoliation process from the synthesized bulk ingot. Different amounts of SnSe nanosheets were evenly distributed in the PEDOT:PSS matrix, producing various SnSe/PEDOT:PSS composites. The thermal conductivity of the composites was found to be insensitive to the addition of SnSe nanosheets. The power factor of the composite film was greatly enhanced by the addition of an optimal content of SnSe nanosheets, which significantly increased the Seebeck coefficient, and the solvent treatment, which dramatically improved the electrical conductivity. The maximum power factor of 386μW/mK<SUP>2</SUP> was obtained for the 5vol.% dimethyl sulfoxide (DMSO)-treated SnSe/PEDOT:PSS composite film with 20wt.% of SnSe nanosheet content, which is ∼257 times higher than that of the pristine PEDOT:PSS film. The use of conductive PEDOT:PSS matrix mixed with inorganic SnSe nanosheets and the subsequent solvent treatment appear a promising strategy to achieve high-performance polymer-based thermoelectric devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SnSe nanosheets are prepared from bulk by Li-intercalation and exfoliation process. </LI> <LI> SnSe/PEDOT:PSS composites are fabricated and show high thermoelectric performance. </LI> <LI> Introduction of SnSe nanosheets contribute to the enhancement of Seebeck coefficient. </LI> <LI> Solvent treatment greatly enhances electrical conductivity of the composite. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced thermoelectric performance of highly conductive poly(3,4-ethylenedioxythiophene)/carbon black nanocomposites for energy harvesting

Ju, Hyun,Kim, Myeongjin,Kim, Jooheon Elsevier 2015 MICROELECTRONIC ENGINEERING Vol.136 No.-

<P><B>Abstract</B></P> <P>The thermoelectric performance of <I>para</I>-methylbenzenesulfonate (<I>p</I>-MeBzs) doped highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) can be improved by the use of carbon black fillers. Thermoelectric nanocomposites were prepared via chemical polymerization. Dodecylbenzenesulfonic acid (DBSA) was introduced before polymerization to act simultaneously as a surfactant for formation of micelles of carbon black and as a doping agent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the morphology of PEDOT coated carbon black and PEDOT. Electrical conductivity of the composites improved with increase in weight percentage of carbon black from 0% to 30%. Extended chain conformations and increase in electron delocalization reduces the carrier hopping barriers. These contribute to the enhancement of charge carrier mobility. Although electrical conductivity is directly proportional to the increase in the filler content, Seebeck coefficient is more or less constant. Relatively small changes of thermal conductivity can be attributed to the phonon scattering effect in both the carbon black and the thermally insulating PEDOT layers. This study reports that the power factor of the composite was estimated to be 0.993μW/mK<SUP>2</SUP> for 10wt% filler content and was more than 1.7 times higher than that for pure PEDOT, and the maximum figure of merit (<I>ZT</I>) value was 0.0012 at room temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesized 0–30% carbon black/PEDOT composites show high thermoelectric efficiency. </LI> <LI> PEDOT layer coating the filler has an affinity to help its dispersion into the matrix. </LI> <LI> Strong conductive network between filler and matrix improves electrical conductivity. </LI> <LI> The Seebeck coefficient remains almost constant with filler load. </LI> <LI> Small changes in thermal conductivity are attributed to the phonon scattering effect. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Organic acid-assisted chemical transformation of SnSe bulk crystals into Se nanowires and the influence on thermoelectric behaviors

Ju, Hyun,Park, Dabin,Kim, Jooheon Elsevier 2018 Journal of alloys and compounds Vol.732 No.-

<P><B>Abstract</B></P> <P>Se nanowires are one of the chalcogenide nanostructures that have attracted interest in various fields of research because of their unique characteristics. The Se nanowires were fabricated from bulk SnSe crystals by an organic acid-assisted chemical transformation process. We found that the concentration of the organic acid during the reaction is critical to control the morphology of the final product. Se nanowires with ∼40 nm diameter and ∼1 μm length were obtained after the transformation, and the reaction mechanism for the chemical transformation was proposed. Moreover, the effect of the Se nanoparticles in SnSe on its thermoelectric behavior was also investigated and discussed. The fabrication method and materials reported in this study will open up new possibilities for various applications with excellent performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Se nanowires are prepared from bulk SnSe crystal by a chemical transformation. </LI> <LI> Reaction mechanism for the chemical transformation process is studied. </LI> <LI> Concentration of organic acid is critical to control the morphology of final product. </LI> <LI> Effect of Se nanoparticles in SnSe on thermoelectric transports is discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Chemically Exfoliated SnSe Nanosheets and Their SnSe/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Composite Films for Polymer Based Thermoelectric Applications

Ju, Hyun,Kim, Jooheon American Chemical Society 2016 ACS NANO Vol.10 No.6

<P>Tin selenide (SnSe) nanosheets (NSs) are prepared by hydrothermal lithium-intercalation and a subsequent exfoliation process from a SnSe ingot. Conducting polymer poly(3,4-ethylenedioxythiohene):poly(styrenesulfonate) (PEDOT:PSS)-based thermoelectric composites are fabricated with varying SnSe NSs content, and the thermoelectric properties of the composites are examined at 300 K. The exfoliated SnSe particles show thin two-dimensional sheet-like structures that are evenly distributed into the PEDOT:PSS matrix. The significantly enhanced power factor (S-2.sigma of the SnSe NS/PEDOT:PSS composites with increasing SnSe NSs content can be explained by the potential difference at the interface between the SnSe and PEDOT:PSS. The fabricated SnSe NS/PEDOT:PSS composites show a maximum figure of merit (ZT) of 0.32 at a SnSe NSs loading of 20 wt %. The mixing of inorganic nanoparticles with the conducting polymer matrix forms products with extremely low thermal conductivities, which is a promising strategy for the realization of polymer based efficient thermoelectric applications.</P>

Fabrication of Polyaniline-Coated SnSeS Nanosheet/Polyvinylidene Difluoride Composites by a Solution-Based Process and Optimization for Flexible Thermoelectrics

Ju, Hyun,Park, Dabin,Kim, Jooheon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.14

<P>The fabrication of dodecylbenzenesulfonic acid-doped polyaniline (PANI)-coated SnSe<SUB>0.8</SUB>S<SUB>0.2</SUB> (PANI-SnSeS) nanosheets and their application to flexible thermoelectric composite films are demonstrated. The thermoelectric power factor of PANI-SnSeS nanosheets was optimized by manipulating the number of PANI coating cycles, and changes in their electrical conductivity and Seebeck coefficients were investigated and analyzed by considering carrier transport properties. An optimized, solution-based procedure for introducing inorganic nanoparticles comprising PANI-SnSeS nanosheets into a polyvinylidene fluoride (PVDF) matrix maximized the power factor. A composite film with a PANI-SnSeS nanosheet-to-PVDF weight ratio of 2:1 showed outstanding durability and thermoelectric performance, exhibiting a maximum power factor of ∼134 μW/m·K<SUP>2</SUP> at 400 K. These results demonstrate that the incorporation of conductive PANI into SnSeS nanosheets can facilitate high-performance flexible thermoelectric applications.</P> [FIG OMISSION]</BR>

A Strategy for Low Thermal Conductivity and Enhanced Thermoelectric Performance in SnSe: Porous SnSe_1–<i>x</i>S_<i>x</i> Nanosheets

Ju, Hyun,Kim, Myeongjin,Park, Dabin,Kim, Jooheon American Chemical Society 2017 Chemistry of materials Vol.29 No.7

<P>A higher figure of merit (ZT) can be achieved for tin selenide (SnSe)-based thermoelectric materials by significantly reducing the thermal conductivity (kappa) via three promising strategies: substitution with isoelectric atoms, exfoliation of nanosheets (NSs) from a bulk ingot, and chemical transformation of the material into a porous structure. Specifically, SnSe1-xSx NSs are prepared from bulk ingots by hydrothermal Li intercalation and subsequent exfoliation. The substitution of S atoms into SnSe and the fabrication of SnSe1-xSx NSs contribute to the scattering of phonons at a number of atomic disorders and nanosized boundaries, leading to effective reduction of the lc value and an improved ZT. The introduction of porosity into the material through the chemical transformation process results in further reduction of kappa, which leads to a higher ZT. The fabricated porous SnSe0.8S0.2 NS has a maximal ZT value of 0.12 at 310 K, which is significantly higher than that of pristine SnSe.</P>

Solution-processable flexible thermoelectric composite films based on conductive polymer/SnSe_0.8S_0.2 nanosheets/carbon nanotubes for wearable electronic applications

Ju, Hyun,Park, Dabin,Kim, Jooheon The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.14

<P>Flexible thermoelectric composite films consisting of conductive polyaniline (PANI)-coated SnSe0.8S0.2 nanosheets (NSs) and polyvinylidene fluoride (PVDF) are fabricated <I>via</I> a solution processing procedure. The SnSe0.8S0.2 NSs are chemically exfoliated from a bulk ingot, and camphorsulfonic acid-doped PANI (CSA-PANI) is coated on the surface of the SnSe0.8S0.2 NSs. The thermoelectric properties of the composite film can be further enhanced by introducing a small amount of carbon nanotubes (CNTs) into the composite. The maximum thermoelectric power factor of the CSA-PANI-coated SnSe0.8S0.2 NS/PVDF/CNT composite film is 297 μW m<SUP>−1</SUP> K<SUP>−2</SUP> at 400 K, which is significantly higher than that of the CSA-PANI-coated SnSe0.8S0.2 NS/PVDF composite film without CNTs. The incorporation of SnSe0.8S0.2 NSs and conductive PANI mixed with CNTs is a promising strategy to realize high-performance flexible thermoelectric applications.</P>