镁热还原CO2气体制备介孔石墨烯及其电容特性研究

以CO_2为原料,采用金属镁热还原法,制备出富含介孔结构的石墨烯材料。分别利用X射线衍射、扫描电镜、透射电镜、拉曼光谱和N_2吸附-脱附等测试手段对材料的微观结构进行了表征。通过在镁粉中加入不同质量的MgO,可以实现对石墨烯形貌和孔结构的调控,当MgO/Mg质量比为8∶1时,产物(MRG-8)具有均一的介孔结构(4nm)。并对材料的电化学性能进行了测试,在1mol/L KOH的电解液中,MRG-8具有最高的比电容(171F/g),同时具有非常好的倍率特性,循环测试12000周,比电容保持率为94%。当采用[EMIM][BF4]离子液体作为电解液,以MRG-8为电极材料组装成的对称型超级电容器显示出超高功率密度(175k W/kg),对应的能量密度为28.1Wh/kg。因此,采用此方法制备的介孔石墨烯材料在高功率的超级电容器领域具有潜在的应用前景。     

镁热还原法制备圆片状氮化硼多晶微粉

采用三氧化二硼(B₂O₃)、氯化铵(NH₄Cl)和镁粉为反应物, 以三氧化二铁(Fe₂O₃)为催化剂, 利用镁热还原法在700～850 ℃下反应, 制备了氮化硼多晶微粉. X射线衍射(XRD)分析表明, 产物为六方相, 晶格常数a=0.2499 nm, c=0.6682 nm. 产物的红外光谱中在790和1380 cm^-1处出现了六方氮化硼的特征吸收峰. 利用扫描电子显微镜(SEM)观察到产物为圆片状颗粒, 平均直径约为0.9 μm, 平均厚度约为100 nm. 讨论了Fe2O3的存在对产物形成的影响.     

Fabrication of SiC and Si3N4 Whiskers under Pressurized Ar and N2 Atmosphere through High‐Energy Ball Milling

SiO_{2 (activated or mesoporous silica)}/Mg_{(magnesiothermic or metal sintering aid)}/C_{(activated or polymeric carbon)}/N_{2 (atmosphere)} systems were used in the one‐step synthesis of β‐SiC and β‐Si₃N₄ whiskers. In this study, a mixture of the active precursors was allowed to react via a self‐sustaining reaction (high‐energy ball milling process). Scanning electron micrographs and X‐ray diffraction (XRD ) analysis showed that the rod‐like SiC whiskers (~800 µm) were synthesized in situ by the direct carbothermal reduction of silicon nitride (or silicon) with activated carbon in N₂ (or Ar) atmosphere. The results show that β‐Si₃N₄ (without β‐SiC ) was fully formed after 5 h of milling with four different morphologies, namely whisker tip (droplet/no droplet) and nonuniform whiskers (short hexagonal/rhombohedral/rod‐like) with a length of 0.1–400 µm. By adding metal sintering aids, the liquid phase Mg–Si–O–N and the rate of carbothermal reduction increased (enhanced densification via particle rearrangement) and their hexagonal whiskers tended to assume a rod‐like shape. The effect of the concentration of CO (reduction of α‐Fe₂O₃ to Fe by CO ) on the whisker synthesis suggests that, in addition to the concentration of CO , the nature of the family of mesoporous silica/carbon template is an important factor in the synthesis of β‐SiC and β‐Si₃N₄ whiskers. The possible chemical reactions were investigated by studying the unwanted phases (MgO , Si, SiC , Fe₂O₃ , Fe₃O₄ , FeO , Fe, Fe₃C , MgCO₃ ) of comparable XRD graphs.     

Porous Si/C composite as anode materials for high-performance rechargeable lithium-ion battery

A novel porous silicon was synthesized through a magnesiothermic reduction method of molecular sieve for the first time, the porous silicon was used as anode material, which shows a high initial specific capacity of 2018.5 mAh/g with current density of 0.1 A/g.     

A New Route to High Yield Mesostructure Boron Carbide Powder from SiC/Si3N4 Whiskers

Boric acid/Mg (magnesiothermic or metal sintering aid)/C (activated carbon)/N₂ or Ar (atmosphere)/additives (mesoporous SiO₂ or mesoporous SiC or SiC/Si₃N₄ whiskers) systems were used in the one‐step synthesis of mesostructured B₄C (221.04 m²/g). In this study, a mixture of the active precursors was allowed to react via a self‐sustaining reaction (high‐energy ball milling process). Also, the properties of the samples prepared using powdered activated carbon (PAC) and SiC/Si₃N₄ whiskers (concentration in the range 5–10 wt%) as sources of carbon were investigated. X‐ray diffraction results proved the presence of crystalline boron carbide in the peak positions of B₄C (B₁₂C₃). The advantage of the present route for yielding mesostructured B₄C powder seems to be limited by the growth of carbide crystals. This restriction is believed to be imposed by a lack of whisker additives around the pores where B₄C crystals grow. The results also show that the best mesoporous additive for the synthesis of nanoscale boron carbide is mesoporous SiC. The effect of the concentration of CO (reduction of α‐Fe₂O₃ to Fe by CO) on the B₄C synthesis suggests that, in addition to the concentration of CO, the pressure of the N₂ atmosphere is an important factor in the synthesis of mesostructured B₄C.     

无序介孔硅复合纳米结构的制备与慢活化行为

通过对SiO_2纳米粒子进行镁热还原及后处理,制备了多级无序Si介孔复合纳米结构MP-Si@SiO_x@C,此结构展现出容量非衰减缓升的电化学慢活化行为,可抵消循环容量常规衰减趋势,赋予负极优良的循环稳定性.通过X射线衍射(XRD)、透射电子显微镜(TEM)、场发射扫描电子显微镜(SEM)、N_2吸附-脱附测试和孔径分布模拟分析发现,Si介孔组织包含微-窄介孔(1~5 nm)、中介孔(5~20 nm)以及大介孔-宏孔(20~100 nm)三级孔道,分别源于原初级粒子内部孔道、粒子团聚堆垛与粒内酸蚀、团聚体再堆垛;此合成装配方法有效提升了Si材料的堆积密度,电池电极能获得较高的体积比容量和储能密度.     

多孔硅的模板限制镁热还原法制备及性能

采用一种基于气-固反应机制的模板限制镁热还原法,以SiO2气凝胶为模板在低温(650℃)下制备出一种高比表面积纳米多孔硅材料.利用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)和比表面积(BET)分析等表征手段对样品的成分、物相结构、微观形貌和孔结构进行分析,并初步研究了材料的光学特性和电化学性能.结果表明,产物为纳米硅晶体颗粒组成的多孔结构,保留了与原始气凝胶模板相似的微观形貌,比表面积高达602 m2·g-1.该材料在室温下表现出显著的红光光致发光特性,且具有较高的储锂容量和较好的嵌入/脱出锂性能.     

镁热还原法制备有序介孔Si/C锂离子电池负极材料及其电化学性能

以SBA-15为前驱体,在660 ℃下通过镁热还原反应得到介孔硅材料,并对其进行碳包覆处理,成功地制备了有序介孔Si/C（OMP-Si/C）复合材料。该OMP-Si/C材料保留了SBA-15模板的有序蜂窝孔道,并且形成具有高堆积密度的莲藕链束结构。文中还提出了一个SBA-15镁热还原液态环境反应模型,探讨了660 ℃下硅的高度有序介孔与莲藕链束结构的形成机理。利用X射线衍射（XRD）仪、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、氮气吸脱附法及拉曼光谱对样品物相和微观形貌进行了表征。这种高度有序介孔Si/C复合材料具有优异的电化学性能,展现出其在第二代锂电池负极材料领域中的潜在应用价值。