氮掺杂碳纳米材料在氧还原反应催化剂中的研究进展

长期以来,碳材料负载高分散的铂催化剂及其合金材料一直是商业化质子交换膜燃料电池（PEMFC）中氧还原反应和氢氧化反应十分有效的催化剂。但由于Pt基催化剂成本高、电化学条件下稳定性差、易CO中毒以及氧还原反应（ORR）动力学迟缓等一系列问题,阻碍了其在燃料电池中的进一步应用和大规模生产。相比之下,氮掺杂碳纳米材料具有低成本、高活性、高稳定性、环境友好等特点,这些优异的性能使其在燃料电池领域有着广阔的应用前景。结合近几年国内外研究现状,综述了原位掺杂法、后掺杂合成法和直接热解法等3种氮掺杂碳纳米材料的制备方法,并分析了各自的优点和不足之处,及其作为ORR催化剂的研究进展。最后,对未来氮掺杂碳纳米材料催化剂研究的主要发展方向进行了展望。     

反应条件对原位聚合聚苯胺薄膜性能影响

利用分散聚合法,在玻璃基体表面原位聚合沉积得到透明导电聚苯胺(PANI)薄膜,考察了反应条件对PANI薄膜形貌、电导率等性能的影响。结果表明,反应温度选用冰水浴(0℃),氧化聚合反应温和,薄膜质量高;氧化剂APS(过硫酸铵)加入方式的细化,有利于改善薄膜的表观形貌和电导率;利用硅烷偶联剂OTS(十八烷基三氯硅烷)处理玻璃表面,得到的PANI薄膜更加细密均匀,电导率也显著提高;换用磷酸为掺杂酸,得到的PANI薄膜表观质量差,电导率低。     

过渡金属/氮共掺杂碳材料在氧电极电催化中的研究进展

氧还原反应(ORR)和氧析出反应(OER)是金属-空气电池(MAB)等电化学能量转换技术中的关键化学过程,然而缓慢的ORR和OER动力学限制了MAB的应用,同时Pt基与Ru基催化剂虽然有优异的ORR/OER性能,但由于价格昂贵,资源稀缺限制了发展,因此研究者们开始关注过渡金属。氮掺杂碳材料作为阴极电极具有良好的双功能,但仍需改进,因此过渡金属与氮共掺杂碳基催化剂成为研究的热点,综述了近年来过渡金属/氮共掺杂碳基电催化剂的研究进展。     

氮掺杂石墨烯/多孔碳复合材料的制备及其氧还原催化性能

采用简单、无模板的方法制备了氮掺杂多孔石墨烯/碳复合材料(NPGC)。采用SEM、XRD、Raman、XPS等分析手段对NPGC的形貌、组成以及结构进行了表征,利用旋转圆盘电极技术测试了其电催化氧还原反应(ORR)活性。结果表明,葡萄糖在水热后生成的碳与石墨烯成功复合,并在950℃炭化、活化后形成了相互渗透、结构良好的三维片状多孔网络结构;其氮含量高达9.47%。NPGC作为一种高效的非金属ORR电催化剂,在碱性溶液中具有较高的起始电位[0.87 V(vs RHE)]和较大的极限电流密度(4.7 mA?cm^?2),以及其ORR平均转移电子数为3.8。与商业Pt/C催化剂相比,NPGC具有较强的耐甲醇性和长期耐久性,且制备成本较低,具有广阔的应用前景。     

白光LED用硅基氮(氧)化物荧光转换材料的研究进展

硅基氮(氧)化物荧光转换材料的结构由SiX_4(X=O,N) 四面体形成的网络组成,具有优异的热和化学稳定性以及优良的荧光性能,成为白光LED的理想下转换荧光材料.本文在综述了硅基氮(氧)化物材料体系和荧光性能的基础上,分析和讨论了硅基氮(氧)化物荧光发光材料的发光机理与性能改进.最后展望了硅基氮(氧)化物荧光转换材料的发展趋势和在白光LED中的应用前景.     

吡啶苯并二氮(艹卓)氧化反应的研究

以2-氯-3-硝基吡啶（Ⅱ）为起始原料,通过取代、还原两步反应合成化合物N^2-甲基-N^2-苯基吡啶-2,3-二胺（Ⅳ）。化合物Ⅳ分别与正丙酸、正丁酸和苯乙酸进行关环反应,得化合物三环类苯并二氮蕈（Ⅴ）。室温条件下,向化合物Ⅴ的二氯甲烷溶液中通入氧气,得到氧化产物含羰基的三环类苯并二氮蕈（Ⅰ）,收率为62．0％～95．5％,并经过HPLC-MS和核磁共振分析证明为目的产物。所得产物为新药物的研发提供了结构新颖的化合物。     

基于ZIF-8衍生氮掺杂多孔碳的高稳定性氧还原催化剂

沸石咪唑脂框架8(ZIF-8),高温热解处理得到氮掺杂多孔碳(NPC),通过双溶剂浸渍法、化学还原法以及酸处理,制备了NPC负载铂铜的开放型合金纳米颗粒催化体系。通过形貌表征和氧还原催化活性测试,筛选出最佳催化剂,该催化剂也在电流-时间测试中,表现出卓越的稳定性。其催化性能的提升,主要基于铜的引入对金属铂的d带中心的调控以及NPC中氮掺杂位点、羰基官能团对于金属纳米颗粒的锚定作用。     

以氨水为沉淀剂反应条件对储氧材料性能的影响

以氨水为沉淀剂制备一系列储氧材料,表征了其物相组成,同时对其储氧性能和比表面积进行了测定,探讨了反应条件对储氧材料性能的影响.结果表明,前驱体到最终CeO2-ZrO2固溶体的形成是属于同晶相转化;pH值、陈化温度、反应物浓度对材料的储氧性能、比表面积、抗老化性能有着不同程度的影响.     

利用氧氮分析仪测定类石墨增碳剂中氮含量

应用氧氮分析仪,采取下进样方式对石墨增碳剂中的氮含量进行分析研究,经过可行性实验分析得知,当称样量超过0.25g之后实验数据逐渐稳定.此外,同一种样品使用铣床与钻床的加工屑样结果相同,说明氮元素含量基本一致.     

In Situ Reaction Synthesis of Silicon Carbide–Boron Nitride Composite from Silicon Nitride–Boron Oxide–Carbon

This work proposes a new approach, based on the reaction Si₃N₄+ 2B₂O₃+ 9C → 3SiC + 4BN + 6CO, to synthesize an SiC–BN composite. The composite was prepared by reactive hot pressing (RHP), at 2000°C for 60 min at 30 MPa under an argon atmosphere, following a 60 min hold at 1700°C without applied pressure before reaching the RHP temperature. TG-DTA results showed that a nitrogen atmosphere inhibited denitrification somewhat and retarded the reaction rate. The chemical composition of the obtained material was consistent with theoretical values. FE-SEM observation showed that in situ -formed SiC and BN phases were of spherical morphology with very fine particle size of ∼100 nm.     

Bonding of Dense Silicon Nitride with Carbon Interlayers

Diffusion bonding of dense Si₃N4 containing 10% Ce₂O₃, 7% A1₂O₃, and 2% Y₂O₃ was attempted through hot pressing at temperatures of 1000° to 1400°C. Physically vapor-deposited (PVD) carbon and paraffin-wax candle soot were tried as interlayers. The interfaces were analyzed through optical and scanning electron microscopy, and through X-ray photoelectron spectroscopy. The bonding temperature could be reduced from 1400° (without interlayers) to 1100°C with PVD carbon or candle soot. From C Is and Si 2p spectra, the formation of SiC at the interface through the reaction of C with the silicon oxynitride layer has been identified.     

氮化硅料浆的流变性能

研究了分散剂加入量,球磨时间,料浆固相含量,料浆ＰＨ值对含烧结助剂α－Ａｌ２Ｏ３,Ｙ２Ｏ３的氮化硅浆的流变性能的影响。     

Elevated-Temperature Mechanical Properties of Silicon Nitride/Boron Nitride Fibrous Monolithic Ceramics

A unique, all-ceramic material capable of nonbrittle fracture via crack deflection and delamination has been mechanically characterized from 25° through 1400°C. This material, fibrous monoliths, was comprised of unidirectionally aligned 250 μm diameter silicon nitride cells surrounded by 10 to 20 μm thick boron nitride cell boundaries. The average flexure strengths of fibrous monoliths were 510 and 290 MPa for specimens tested at room temperature and 1300°C, respectively. Crack deflection in the BN cell boundaries was observed at all temperatures. Characteristic flexural responses were observed at temperatures between 25° and 1400°C. Changes in the flexural response at different temperatures were attributed to changes in the physical properties of either the silicon nitride cells or boron nitride cell boundary.     

Carbothermal Synthesis of Silicon Nitride: Effect of Reaction Conditions

Conditions for carbothermal synthesis of α-Si₃N₄ are presented with special emphasis on the reaction temperature, C:SiO₂ ratio, and precursor mixing. With pure precursors, the conversion temperature is 1500° to 1550°C. An excess of C is necessary for complete conversion, and a simple sol–gelmixing technique provides excellent intermixing of the precursors. Copious flow of N₂ gas throughout the reactor bed is essential if pure Si₃N₄ is to be produced; small concentrations of CO and O₂ promote SiC and Si₂N₂O, respectively.     

Mechanical Properties of Three-Layered Monolithic Silicon Nitride–Fibrous Silicon Nitride/Boron Nitride Monolith

A three-layered composite, composed of a strong outer layer (monolithic S₃N₄) and a tough inner layer (fibrous Si₃N₄/BN monolith), was fabricated by hot-pressing. For the inner layer, a Si₃N₄–polymer fiber made by extrusion was coated by dipping it into a 20 wt% BN-containing slurry. The three-layered composite exhibited excellent mechanical properties, including high strength, work of fracture, and crack resistance, because of the combination of a strong outer layer and a tough inner layer. In other words, the strong outer layer withheld the applied stress, while the tough inner layer promoted crack interactions through the weak BN cell boundaries. Also, the residual thermal stress on the surface due to the anisotropy in the coefficient of thermal expansion of BN affected a median/radial crack generation after indentation.     

Silicon Nitride and Related Materials

Silicon nitride has been researched intensively, largely in response to the challenge to develop internal combustion engines with hot-zone components made entirely from ceramics. The ceramic engine programs have had only partial success, but this research effort has succeeded in generating a degree of understanding of silicon nitride and of its processing and properties, which in many respects is more advanced than of more widely used technical ceramics. This review examines from the historical standpoint the development of silicon nitride and of its processing into a range of high-grade ceramic materials. The development of understanding of microstructure–property relationships in the silicon nitride materials is also surveyed. Because silicon nitride has close relationships with the SiAlON group of materials, it is impossible to discuss the one without some reference to the other, and a brief mention of the development of the SiAlONs is included for completeness.     

Fabrication of Low-Shrinkage, Porous Silicon Nitride Ceramics by Addition of a Small Amount of Carbon

Successful net-shape sintering offers a significant advantage for producing large or complicated products. Porous Si₃N₄ ceramics with very low shrinkage were developed, in the present investigation, by the addition of a small amount of carbon. Carbon powders (1–5 vol%) of two types, with different mean particle sizes (13 nm and 5 μm), were added to α-Si₃N₄−5 wt% Y₂O₃ powders. SiC nanoparticles formed through reaction of the added carbon with SiO₂ on the Si₃N₄ surface or with the Si₃N₄ particles themselves. Such reaction-formed SiC nanoparticles apparently had an effective reinforcing effect, as in nanocomposites. Sintered Si₃N₄ porous ceramics with a high porosity of 50%–60%, a very small linear shrinkage of ∼2%–3%, and a strength of ∼100 MPa were obtained.     

Reactivity of Aluminum Nitride Powder in Aqueous Silicon Nitride and Silicon Carbide Slurries

The reactivity of AlN powder with water in supernatants obtained from centrifuged Si₃N₄ and SiC slurries was studied by monitoring the pH versus time. Various Si₃N₄ and SiC powders were used, which were fabricated by different production routes and had surfaces oxidized to different degrees. The reactivity of the AlN powder in the supernatants was found to depend strongly on the concentration of dissolved silica in these slurries relative to the surface area of the AlN powder in the slurry. The hydrolysis of AlN did not occur if the concentration of dissolved silica, with respect to the AlN powder surface, was high enough (1 mg SiO₂/(m² AlN powder)) to form a layer of aluminosilicates on the AlN powder surface. This assumption was verified by measuring the pH of more concentrated (31 vol%) Si₃N₄ and SiC suspensions also including 5 wt% of AlN powder (with respect to the solids).     

Machinability of Silicon Nitride/Boron Nitride Nanocomposites

The machinability and deformation mechanism of Si₃N₄/BN nanocomposites were investigated in the present work. The fracture strength of Si₃N₄/BN microcomposites remarkably decreased with increased hexagonal graphitic boron nitride ( h -BN) content, although machinability was somewhat improved. However, the nanocomposites fabricated using the chemical method simultaneously had high fracture strength and good machinability. Hertzian contact tests were performed to clarify the deformation behavior by mechanical shock. As a result of this test, the damage of the monolithic Si₃N₄ and Si₃N₄/BN microcomposites indicated a classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation.