Yanrong Li

Fabrication and characterization of polyaniline-based gas sensor by ultra-thin film technology

Abstract Pure polyaniline (PAN) film, polyaniline and acetic acid (AA) mixed film, as well as PAN and polystyrenesulfonic acid (PSSA) composite film with various number of layers were prepared by Langmuir–Blodgett (LB) and self-assembly (SA) techniques. These ultra-thin films were characterized by ultraviolet–visible (UV–VIS) spectroscopy and ellipsometry. It is found that the thickness of PAN-based ultra-thin films increases linearly with the increase of the number of film layers. The gas-sensitivity of these ultra-thin films with various layers to NO 2 was studied. It is found that pure polyaniline films prepared by LB technique had good sensitivity to NO 2 , while SA films exhibited faster recovery property. The response time to NO 2 and the relative change of resistance of ultra-thin films increased with the increase of the number of film layers. The response time of three-layer PAN film prepared by LB technique to 20xa0ppm NO 2 was about 10xa0s, two-layer SA film was about 8xa0s. The mechanism of sensitivity to NO 2 of PAN-based ultra-thin films was also discussed.

Two-dimensional semiconductors with possible high room temperature mobility

We have calculated the longitudinal acoustic phonon limited electron mobility of 14 two-dimensional semiconductors with composition of MX2, where M (= Mo, W, Sn, Hf, Zr and Pt) is the transition metal, and X is S, Se and Te. We treated the scattering matrix by the deformation potential approximation. We found that out of 14 compounds, MoTe2, HfSe2 and ZrSe2 are promising regarding to their possible high mobility and finite band gap. The phonon limited mobility can be above 2,500 cm2·V−1·s−1 at room temperature.

Flexible Graphene-Based Electroluminescent Devices

For the first time, large-area CVD-grown graphene films transferred onto flexible PET substrates were used as transparent conductive electrodes in alternating current electroluminescence (ACEL) devices. The flexible ACEL device based on a single-layer graphene electrode has a turn-on voltage of 80 V; at 480 V (16 kHz), the luminance and luminous efficiency are 1140 cd/m(2) and 5.0 lm/W, respectively. The turn-on voltage increases and the luminance decreases with increasing stacked layers of graphene, which means the single-layer graphene is the best optimal choice as the transparent conductive electrode. Furthermore, it demonstrates that the graphene-based ACEL device is highly flexible and can work very well even under a very large strain of 5.4%, suggesting great potential applications in flexible optoelectronics.

From Metal–Organic Framework to Li2S@C–Co–N Nanoporous Architecture: A High-Capacity Cathode for Lithium–Sulfur Batteries

Owing to the high theoretical specific capacity (1166 mAh g-1), lithium sulfide (Li2S) has been considered as a promising cathode material for Li-S batteries. However, the polysulfide dissolution and low electronic conductivity of Li2S limit its further application in next-generation Li-S batteries. In this report, a nanoporous Li2S@C-Co-N cathode is synthesized by liquid infiltration-evaporation of ultrafine Li2S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) derived from metal-organic frameworks. The obtained Li2S@C-Co-N architecture remarkably immobilizes Li2S within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C-Co-N and Li2S nanoparticles, the Li2S@C-Co-N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g-1 after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g-1 at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li-S batteries.

Three-Dimensional Hierarchical Reduced Graphene Oxide/Tellurium Nanowires: A High-Performance Freestanding Cathode for Li–Te Batteries

Three-dimensional aerogel with ultrathin tellurium nanowires (TeNWs) wrapped homogeneously by reduced graphene oxide (rGO) is realized via a facile hydrothermal method. Featured with high conductivity and large flexibility, the rGO constructs a conductive three-dimensional (3D) backbone with rich porosity and leads to a free-standing, binder-free cathode for lithium-tellurium (Li-Te) batteries with excellent electrochemical performances. The cathode shows a high initial capacity of 2611 mAh cm(-3) at 0.2 C, a high retention of 88% after 200 cycles, and a high-rate capacity of 1083 mAh cm(-3) at 10 C. In particular, the 3D aerogel cathode delivers a capacity of 1685 mAh cm(-3) at 1 C after 500 cycles, showing pronounced long-cycle performance at high current density. The performances are attributed to the well-defined flexible 3D architecture with high porosity and conductivity network, which offers highly efficient channels for electron transfer and ionic diffusion while compromising volume expansion of Te in charge/discharge. Owing to such advantageous properties, the reported 3D rGO/tellurium nanowire (3DGT) aerogel presents promising application potentials as a high-performance cathode for Li-Te batteries.

Pure thiophene-sulfur doped reduced graphene oxide: synthesis, structure, and electrical properties

Here we propose, for the first time, a new and green ethanol-thermal reaction method to synthesize high-quality and pure thiophene-sulfur doped reduced graphene oxide (rGO), which establishes an excellent platform for studying sulfur (S) doping effects on the physical/chemical properties of this material. We have quantitatively demonstrated that the conductivity enhancement of thiophene-S doped rGO is not only caused by the more effective reduction induced by S doping, but also by the doped S atoms, themselves. Furthermore, we demonstrate that the S doping is more effective in enhancing conductivity of rGO than nitrogen (N) doping due to its stronger electron donor ability. Finally, the dye-sensitized solar cell (DSCC) employing the S-doped rGO/TiO2 photoanode exhibits much better performance than undoped rGO/TiO2, N-doped rGO/TiO2 and TiO2 photoanodes. It therefore seems promising for thiophene-S doped rGO to be widely used in electronic and optoelectronic devices.

Self-assembly of polyaniline ultrathin films based on doping-induced deposition effect and applications for chemical sensors

Abstract Electroactive nanocomposite ultrathin films of polyaniline (PAN) and isopolymolybdic acid (PMA) were fabricated by a novel molecular self-assembling process based on the alternate deposition of PAN and PMA from their dilute solutions. The process was based on doping-induced deposition effect of emeraldine base. The process was monitored by UV/VIS spectroscopy measurement. It was found that the conductivity of the PAN films is sensitive to humidity, NO2 and NH3. The technique may be used to fabricate chemical sensors and other molecular devices.

Self-Assembled Coral-like Hierarchical Architecture Constructed by NiSe2 Nanocrystals with Comparable Hydrogen-Evolution Performance of Precious Platinum Catalyst

For the first time, self-assembled coral-like hierarchical architecture constructed by NiSe2 nanocrystals has been synthesized via a facile one-pot DMF-solvothermal method. Compared with hydrothermally synthesized NiSe2 (H-NiSe2), the DMF-solvothermally synthesized nanocrystalline NiSe2 (DNC-NiSe2) exhibits superior performance of hydrogen evolution reaction (HER): it has a very low onset overpotential of ∼136 mV (vs RHE), a very high cathode current density of 40 mA/cm2 at ∼200 mV (vs RHE), and an excellent long-term stability; most importantly, it delivers an ultrasmall Tafel slope of 29.4 mV dec-1, which is the lowest ever reported for NiSe2-based catalysts, and even lower than that of precious platinum (Pt) catalyst (30.8 mV dec-1). The superior HER performance of DNC-NiSe2 is attributed to the unique self-assembled coral-like network, which is a benefit to form abundant active sites and facilitates the charge transportation due to the inherent high conductivity of NiSe2 nanocrystals. The DNC-NiSe2 is promising to be a viable alternative to precious metal catalysts for hydrogen evolution.

Fabrication of self-assembled polyaniline films by doping-induced deposition

Abstract The ultrathin films of polyaniline (PAni)/poly (styrenesulfonic acid)(PSSA) were fabricated via a novel self-assembling process by alternately immersing the substrates into dilute PAni solution in N-methylpyrrolidinone (NMP) and the aqueous solution of PSSA. The process was characterized by UV–Vis absorption spectroscopy. It was found that the oxidation state of polyaniline in single monolayers was dependent on the thickness of the film. The self-assembling mechanism was based on the acid-base reaction between PAni and PSSA. The thickness of the films can be easily manipulated at nanometer scale by controlling the solution chemistry and recycling times. The resulting films are uniform and adhere strongly to the substrates.

Vertically oriented few-layered HfS2 nanosheets: growth mechanism and optical properties

For the first time, large-area, vertically oriented few-layered hafnium disulfide (V-) nanosheets have been grown by chemical vapor deposition. The individual nanosheets are well [001] oriented, with highly crystalline quality. Far different from conventional van der Waals epitaxial growth mechanism for two-dimensional transition metal dichalcogenides, a novel dangling-bond-assisted self-seeding growth mechanism is proposed to describe the growth of V- nanosheets: difficult migration of adatoms on substrate surface results in seeds growing perpendicularly to the substrate; V- nanosheets inherit the growth direction of seeds; V- nanosheets further expand in the in-plane direction with time evolution. Moreover, the V- nanosheets show strong and broadened photons absorption from near infrared to ultraviolet; the V--based photodetector exhibits an ultrafast photoresponse time of 24 ms, and a high photosensitivity ca. 103 for 405 nm laser.