Materials Science Forum Vol. 956

Abstract: As a kind of green, environment-friendly and sustainable carbon material, biomass carbon has simple processing technology and undoubtedly been the best candidate for industrialization. Different activation processes can be used to change the internal microstructure of carbons, and design pores that facilitate ions transport and electrons conduction, thereby achieving the ultimate goal of improving electrochemical performance. Herein, we select the same activator (KOH) and activation time (3 h) but change the activation temperature (300 °C, 600 °C, 800 °C) to obtain biomass-derived carbon with the different micromorphology, pores structure and heteroatoms content. Rather, We choose ether-based electrolyte, due to its highly reversible graphite co-intercalation reaction, the problem of extremely low electrochemical activity of graphite in ester electrolytes is avoided. Results indicate, the sample PCS-600 exhibites sheet structure with specific surface area of 38.3 m²/g and large average pore width of 2.77 nm, which providing sufficient conditions for ions transport. PCS-600 has 1.05 at% N and 5.75 at% O heteroatoms, which providing additional pseudocapacitance. In addition, the electrochemical performance of PCS-600 is optimal, at a current density of 0.1 A/g, its specific capacity is 198.6 mA h/g, maintain at ~95% after 100 cycles, with coulomb efficiency ~100%.

Abstract: The paper aims to provide the methods to tailor the rheological properties of silver paste for improving the fine line printing properties for crystalline silicon solar cells. The investigation on the internal structure model of silver paste was performed in order to understand the interaction among constituents in silver paste. Much stronger polymer network structure is formed through chain entanglements between thixotropic agent and polymer resin compared with the network structure originated from thixotropic agent. Silver particles have some association with above polymer network structure and form a stronger internal structure of silver paste together. The rheological properties were improved by tailoring the composition of polymer resin, using a combination of controlled flocculating dispersing additive and thixotropic agent, and the addition of nanosized carbon black. The strength of internal network structure can be enhanced by the design of polymer resin composition but without increasing high shear-rate viscosity. Through the combination use of controlled flocculating dispersing additive and thixotropic agent, the strength of network structure and viscosity can be improved. The depletion flocculation induced by the addition of nanosized carbon black introduces a new attraction force between silver particles and strengthens the internal network structure.

Abstract: In order to obtain a titanium-based PbO₂ electrode with high electrocatalytic activity and good stability, A porous β-PbO₂ electrode is prepared by electrodepositing on titanium substrate Sn-Sb-RuOx coating. The surface morphology and phase analysis of the porous β-PbO₂ electrode prepared at different current density were investigated by SEM and XRD. Results showed that the current density changes the surface morphology and active surface area of the porous β-PbO₂ electrode. When the current density is 2 A/dm², the surface of the porous β-PbO₂ prepared by electrodeposition has a uniform porous morphology with a pore diameter of 50-200 µm with main crystal phase of β-PbO₂. Influence of current density on the electrochemical activity of the electrode was analyzed using anodic polarization curve, electrochemical impedance spectroscopy and galvanostatic polarization. Results revealed that with the increase of current density, the oxygen evolution potential of the porous β-PbO₂ electrode decreases first and then increases while the exchange current density first increases and then decreases. When the current density is 2 A/dm², the oxygen evolution potential is 2.0075 V(at 0.05 A/cm²) and the maximum exchange current density is 1.77×10^-4 A/cm². According to the electrochemical impedance spectroscopy, when the current density is 2 A/dm², Q_f and Q_dl are the largest, R_f and R_ct are the smallest, and the R_F first increases and then decreases with the current density increases. When the current density is 2 A/dm², the maximum R_F value is 655.7. The results with galvanostatic polarization at current density of 0.05 A/cm² showed that the electrode has a minimum electrode voltage of 2.05 V at a current density of 2 A/dm². Accelerated life experiments were carried out in 2 g/L Cl^- and 150 g/L H₂SO₄ bath at 25 °C, and the porous β-PbO₂ electrode obtained under the current density of 2 A/dm² has the longest life, and the electrode life is 68 h, which is 2.5 times of the PbO₂ electrode obtained under the current density of 4 A/dm².

Abstract: In order to explore the supercapacitor electrode material with high energy density, a composite material that nickel-cobalt sulfide loaded in graphene (NiCo₂S₄@rGO) with core-shell structure was successfully prepared by hydrothermal, room temperature vulcanization and annealing. The core-shell structure of the material greatly increased the contact area between the material and the electrolyte and improved the electrochemical performance. In addition, the energy density has been significantly improved. NiCo₂S₄@rGO was characterized by field emission scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectrometer. The electrochemical properties of the material were evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The results show that the capacitance can reach 1100 F/g at the current density of 0.5 A/g. Furthermore, the NiCo₂S₄@rGO as positive electrode and reduced graphene oxide (rGO) as negative electrode were assembled into an asymmetric supercapacitor (ASC). The device exhibits a high energy density of 74.78 Wh/Kg at a power density of 400 W/Kg, as well as excellent cycling stability of 88.9% after 3 000 cycles, which reflects the excellent electrochemical performance of the material.

Abstract: The influencing effect of pressure on structural stability and elastic properties of PbSe₂ compound is mainly investigated by first-principles method and homogenization method of the Y parameter. The optimized structural parameters at zero pressure are a=b=6.446Å, c=7.887Å (GGA method) and a=b=6.316Å, c=7.651Å (LDA method), which has good agreement with the experimental and theoretical values. Our calculated lattice parameters and Se-Se bond length are in excellent agreement with experimental data. PbSe₂ compound is energetically stable with a good alloying ability. The elastic constants are calculated, and then the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and anisotropy factor are determined. Besides, Y parameter method is used to investigate changes of the Poisson ratio, Young’s and shear moduli of PbSe₂ within different normal orientation crystal planes. Results show that: 1) Young’s modulus is about 48.37 GPa from GGA and 58.87 GPa from LDA by Reuss-Voigt-Hill estimation, which is averaged about 53.62 GPa; 2) The PbSe₂ compound is ductile according to B/G ratio. The universal anisotropic index AU shows that PbSe₂ exhibits a fairly high elastic anisotropy.

Abstract: In this work, a thermal reduction process via ultrafine titanium powder as the reducing agent under argon atmosphere is firstly used to prepare Ti₄O₇. Compared with the conventional method, this experiment process reduces the sintering temperature to 850°C. The phase transformation and the morphology of the as-prepared powders are examined by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Besides, it is found that the Ti₄O₇ powders obtained by titanium thermal reduction method exhibited the crystal structure, distinctly possessing an average particle size around 750 nm. The as-prepared Ti₄O₇ nanoparticles are used as anode active material in lithium battery. The results demonstrate that the anode with Ti₄O₇ calcined at 850°C by titanium thermal reduction method exhibited insertion/extraction lithium ion property.

Abstract: In this paper, alumina ceramics were prepared with alumina powder and lanthanum nitrate. The influence of La₂O₃ on the microstructure and properties of alumina ceramics were studied. The result showed that the addition of La₂O₃ contributed to the mechanical property of the samples. The alumina ceramics with adding of 0.05wt% La₂O₃ sintered at 1490°C had the best mechanical properties. And the flexural strength, fracture toughness of the ceramics could reach 571.902MPa and 5.82MPa•m^1/2，which were improved by 37.55% and 10.65% respectively compared with the alumina ceramics without La₂O₃. Besides, the average grain size of alumina ceramic is about 2.8μm, and the effect of inhibition on grain growth of alumina ceramics was obvious.

Abstract: The effects of temperature and graphite-like structure additive on the graphitization process of amorphous carbon were investigated through molecular dynamics simulation. The molecular models of amorphous carbon and graphite-like structure-amorphous carbon were constructed with the initial density of 1.62 g/cm³ and carbon atoms number of 4096 by rapid quenching method. After annealing treatment at 3200 K, 3600 K and 4000 K respectively, the evolution rules of sp² C atoms and the instantaneous conformations of the graphite-like structure-amorphous carbon system were analyzed to investigate the effects of temperature and graphite-like structure on the graphitization process. It could be found that increasing graphitization temperature properly could improve graphitization degree of amorphous carbon. Addition of graphite-like structure could promote recrystallization of the irregular carbon atoms in amorphous carbon materials, thus accelerating graphitization process and promoting graphitization of the system.

Abstract: A series of flexible graphene/carbon nanotubes (CNTs) hybrid papers were prepared by a facile impregnation method using cellulose papers as substrate. The impregnation cycles and sequence have a great impact on microstructure, electrical conductivity and electromagnetic interference (EMI) shielding performance of graphene/CNTs hybrid papers. The results showed that the surface of cellulose papers was covered by graphene and CNTs, forming continuous conductive networks. The graphene/CNTs hybrid papers achieved a thickness range of 174.7-253.2 μm and areal density range of 26-35.7 g/m², which presented a larger advantage than traditional EMI shielding materials. The electrical conductivity was increased from 0.33 S/cm to 7.63 S/cm with the increase of impregnation cycles from 1 to 5. Furthermore, graphene/CNTs hybrid papers delivered a high EMI shielding effectiveness of 22-32 dB in the frequency of 30-1500MHz, which was superior to single graphene or CNTs papers. Moreover, the electrical conductivity and EMI shielding effectiveness of as-prepared graphene/CNTs hybrid papers presented little decline after even bending 100 times at an angle of 180° owing to their excellent flexibility. The graphene/CNTs hybrid papers possess a huge application potential in electromagnetic compatibility (EMC) of electronic device. Key words: graphene; carbon nanotubes; electromagnetic interference shielding; cellulose paper; dielectric polarization