Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

Structural Analysis of silica aerogels for the interlayer dielectric in semiconductor devices

As semiconductor devices have become miniaturized and highly integrated, interconnection problems such as RC delays, power dissipation, and crosstalk appear. To alleviate these problems, materials with a low dielectric constant should be used for the interlayer dielectric in nanoscale semiconductor devices. Silica aerogel as a porous structure composed of silica and air can be used as the interlayer dielectric material to achieve a very low dielectric constant. However, the problem of its low stiffness needs to be resolved for the endurance required in planarization. The purpose of this study is to discover the geometric effect of the electrical and mechanical properties of silica aerogel. The effects of porosity, the distribution of pores, the number of pores on the dielectric constant, and elastic modulus were analyzed using FEM. The results suggest that the porosity of silica aerogel is the main parameter that determines the dielectric constant and it should be at least 0.76 to have a very low dielectric constant of 1.5. Additionally, while maintaining the porosity of 0.76, the silica aerogel needs to be designed in an ordered open pores structure (OOPS) containing 64 or more pores positioned in a simple cubic lattice point to endure in planarization, which requires an elastic modulus of 8 GPa to prevent delamination.     

Highly stable nanocarbon supported Pt catalyst for fuel cell via a molten salt graphitization strategy

Proton exchange membrane fuel cells (PEMFCs) durability has been severely hindered by carbon support poor stability in the cathodic Pt-based catalyst. Herein, a high-surface-area nitrogen-doped graphitic nanocarbon (N-G-CA) with mesopores is developed as Pt support to address PEMFCs durability challenge. Resorcinol-formaldehyde aerogel pyrolyzed carbon aerogel is selected as N-G-CA raw material. Nitrogen atoms are introduced into carbon aerogel via NH₃ heat treatment. Then, nitrogen-doped carbon aerogel is transferred into N-G-CA via heating together with transition-metal salts (one of FeCl₃, FeCl₂, CoCl₂, or MnCl₂, etc.) at 1200 °C. As ORR catalyst, Pt/N-G-CA half-wave potential only lost 10 mV, after 30, 000 cycles accelerated aging test in the rotating-desk-electrode. Only 12 mV voltage loss at 1.5 A/cm2 is observed, after 5, 000 cycles for membrane electrode. Pt/N-G-CA exhibits superior durability and activity than commercial Pt/C. High durability of Pt/N-G-CA is due to N-G-CA high graphitization extent, as well as the interactions between doping nitrogen and Pt. N-G-CA is promising as stable support for durable Pt-based catalysts in PEMFCs, thanks to enhanced carbon corrosion resistance, uniformly dispersed Pt, and strong support-metals interaction.     

常压干燥合成水玻璃基SiO_2气凝胶

以水玻璃和双氧水为原料一步合成二氧化硅湿凝胶,经老化、溶剂置换及三甲基氯硅烷修饰后,并于常压干燥后获得二氧化硅气凝胶。样品经低温N_2吸附-脱附、红外光谱和扫描电镜测试表明所得二氧化硅气凝胶具有三维多孔结构,且其比表面积可达482 m~2·g~(-1)、平均孔径为24.9nm及表观密度为0.12g·cm~(-3)。     

羟甲基化木质素/纤维素气凝胶粒子的制备、表征及吸附性能

以羟甲基化木质素和纤维素为原料，NaOH/尿素水溶液为溶解体系，采用冷冻干燥法制备羟甲基化木质素/纤维素气凝胶粒子。采用扫描电子显微镜（SEM）、傅里叶变换红外光谱（FT-IR）仪、X射线衍射（XRD）仪、比表面积及孔径分析仪等对其结构进行了表征。研究结果表明：羟甲基化木质素分子通过氢键作用附着在纤维素骨架上，气凝胶内部仍保持三维网状结构，羟甲基化木质素的引入使得气凝胶表面出现明显收缩，网状结构的致密度随着羟甲基化木质素用量提高而逐渐降低；同时气凝胶粒子具有纤维素Ⅱ型红外吸收峰和XRD衍射峰；粒子表现出Ⅱ型吸附/脱附等温线，孔径均在15 nm以下，且随着羟甲基化木质素用量不断提高，比表面积、孔容均有所减小，HKL-4的比表面积为105.3m²/g，孔容为0.336 6cm³/g，孔径为13.67nm。吸附性能分析表明在25℃下吸附5 h，HKL-4气凝胶粒子对金胺O、亚甲基蓝和罗丹明B的吸附量分别为33.06、96.06和43.26mg/g，对亚甲基蓝的饱和吸附量可达208.7 mg/g，吸附过程更符合Langmuir等温吸附模型，主要为单分子层吸附。     

SiO2气凝胶隔热保温涂料研究及保温结构优化设计

石油化工行业是国家节能减排重点工程之一，如果相关设备设施保温不当，不仅会造成严重的热量散失，还会对油水分离和输送等产生影响。本文系统介绍了传统的以中空玻璃微珠或陶瓷微珠为主要隔热功能填料的隔热保温涂料的保温机理、性能及其存在的问题；以 SiO₂气凝胶为主要功能填料的新型隔热保温涂料研究现状及研究中的技术难点；针对不同应用环境，开发兼具防腐、防开裂、隔热保温功能的复合保温结构设计。本文为研制新型耐高温、高效水性无机隔热保温涂料的研究提供了参考方向，为隔热保温涂料在石油化工领域的工程应用提供分析。     

严寒地区SiO2气凝胶玻璃窗传热分析

建立了二氧化硅(SiO_2)气凝胶中空玻璃窗传热数值模型,采用有限体积法分析了二氧化硅气凝胶厚度和位置对严寒地区玻璃窗传热的影响。结果表明:二氧化硅气凝胶厚度增加,能够提高玻璃窗内表面温度,降低其热流密度。二氧化硅气凝胶厚度为20 mm时,玻璃窗内表面热流密度为67.5 W/m~2。二氧化硅气凝胶位于室内侧能够更有效地减少建筑能耗,其总能耗为60 120 W。     

Electrospun nanofiber composites with micro-/nano-particles for thermal insulation

Polyacrylonitrile (PAN) nanofiber and silica aerogel (SAG) laminated composites were prepared via electrospinning for thermal insulation. Conventional single nozzle and co-axial electrospinning were used to increase the fraction of aerogel particles in the composite sheets while maintaining the mechanical strength of the sheet. When the core-shell electrospinning technique with co-axial nozzle was applied, the proportion of aerogel particles increased two fold without a deterioration of the mechanical properties. The average thermal conductivity of the laminated composite sheet was reduced by approximately 12.5% as compared to the nanofiber composite prepared using the single-nozzle electrospinning technique. For additional reduction in thermal conductivity, hollow glass microspheres (HGM) was inserted between the interlayer spacing of the electrospun sheets to increase the interlayer spacing. When HGM particles were inserted, it was observed that the thermal conductivity decreased by approximately 20% compared to that of the specimen without particles.     

Elastic modulus prediction based on thermal conductivity for silica aerogels and fiber reinforced composites

The speed of sound is a critical parameter in the test of mechanical and thermal properties. In this work, we proposed a testing method to obtain the elastic modulus of silica aerogel from the sound speed formulas. The solid thermal conductivity of the silica aerogel is experimentally measured for predicting the sound speeds, and then the elastic modulus is calculated based on the elasticity sound speed model. The experimental data of the solid thermal conductivity of silica aerogels with different densities are employed and the obtained elastic modulus is fitted as a power-law exponential function of the density. Two existing sound speed models and three groups of available experimental data are also employed to validate the present fitting relation, and good agreement is obtained for the silica aerogel in the density range of 150–350 kg/m³. The fitting formula can also be extended to estimate the elastic modulus of the glass fiber-reinforced silica aerogel composite. The results show that the elastic modulus of the aerogel composite is sensitive to the glass fiber volume fraction, while the thermal conductivity is weakly dependent on the glass fiber volume fraction at room temperature in the studied range of fiber volume fraction.     

Fabrication of ultrafine Gd2O3 nanoparticles/carbon aerogel composite as immobilization host for cathode for lithium‐sulfur batteries

Carbon aerogel (CA), possessing abundant pore structures and excellent electrical conductivity, have been utilized as conductive sulfur hosts for lithium‐sulfur (Li‐S) batteries. However, a serious shuttle effect resulted from polysulfide ions has not been effectively suppressed yet due to the weak absorption nature of CA, resulting in rapid decay of capacity as the cycle number increases. Herein, ultrafine (~3 nm) gadolinium oxide (Gd₂O₃) nanoparticles (with upper redox potential of ~ 1.58 V versus Li⁺/Li) are uniformly in‐situ integrated with CA through directly sol‐gel polymerization and high‐temperature carbonization. The Gd₂O₃ modified CA composites (named as Gdx‐CA, where x means molar ratio of Gd₂O₃ nanoparticles to carbon) are incorporated with S. Then, the products (S/Gdx‐CA) are acted as sulfur host materials for Li‐S batteries. The results demonstrate that adding ultrafine Gd₂O₃ nanoparticles can dramatically improve the electrochemical properties of the composite cathodes. The S/Gd2‐CA electrode (loading with 58.9 wt% of S) possesses the best electrochemical properties, including a high initial capacity of 1210 mAh g^?1 and a relatively high capacity of 555 mAh g^?1 after 50 cycles at 0.1 C. It is noteworthy that the performance of long‐term cycle (350 cycles) for the S/Gd2‐CA (317 mAh g^?1 after 100 cycles and 233 mAh g^?1 after 350 cycles at 1 C) is improved significantly than that of S/CA (150 mAh g^?1 after 150 cycles at 1 C). Overall, the enhancement of electrochemical performances can be due to the strong polar nature of the ultrafine Gd₂O₃ nanoparticles, which provide strong adsorption sites to immobilize S and polysulfide. Furthermore, the Gd₂O₃ nanoparticles present a catalytic effect. Our research suggests that adding Gd₂O₃ nanoparticles into S/CA composite cathode is an effective and novelty method for improving the electrochemical performances of Li‐S batteries.