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.     

晶须对碳碳复合材料组织和力学性能的影响

添加硅灰石(CaO·SiO₂)晶须制备碳纤维预制体, 并在980 ℃下进行化学气相沉积, 高温石墨化处理后制备得到CaO·SiO₂晶须改性的C/C复合材料。利用SEM、金相显微偏光分析以及力学实验等方法研究了预制体结构对基体微观结构、物理性能和力学性能的影响。实验结果表明: 添加CaO·SiO₂晶须会诱导热解炭呈锥形生长, 同时在石墨化过程中会诱导热解炭的组织结构发生有序性转变, 与基体反应生成SiC二次纤维。添加CaO·SiO₂晶须使得复合材料的石墨化度由31.6%提升至41.1%, 导热和导电性能相比于未添加晶须时分别增加了71.7%和14.3%, 复合材料的弯曲强度相比于未添加晶须时提升了5%。     

Effect of matrix content on the performance of carbon paper as an electrode for PEMFC

Porous conducting carbon fiber‐based composite paper is used as an electrode backing in the fuel cell assembly. It not only acts as a channel through which the reactant and product gases pass to and from the bipolar plate and the catalyst site but also helps in the flow of electrons. In order to perform its role efficiently, it should have sufficient strength, high electrical conductivity, and ideal porous structure. Carbon paper has been fabricated, which builds up the required composite properties. Studies have been conducted to optimize the fiber/matrix ratio in the carbon paper, while ensuring the perfect combination of porosity, mechanical strength, and electrical conductivity for an electrode in a proton electrolyte membrane fuel cells. Detail physico‐mechanical and electrochemical characterizations further ascertain that the fiber/matrix ratio plays an important role in tuning the composite properties. The polarization curve of the unit proton exchange membrane (PEM) fuel cell (with an effective electrode area 4 cm²) shows a peak power density of 916 mW/cm² for the sample with fiber/matrix ratio of 65:35, which is almost the same as the commercially available sigracet gas diffusion layer (SGL) carbon paper tested under similar conditions. Further, proportionally enlarging the electrode area to 100 cm² shows that the carbon paper not only shows almost repeatable results in a given set up but also scales up.     

Kinetics of inverse graphitization of detonation sintered nano-diamond/alumina composites

Recently, detonation sintered nano-diamond/alumina composites have appeared and attracted much theoretical and experimental attention. Inspired by core hypothesis of diamond, molecular dynamics was used to analyze the probability of phase transformation between diamond and graphite. The results showed that the very short duration of heating and cooling was beneficial to the stability of nano-diamond in an environment of high temperature. The higher the pressure is, the more stable the diamond would be under high temperature. Therefore, under the condition of short time, high temperature and high pressure, the probability of diamond-graphite transition of detonation sintered nano-diamond/alumina composites was only equal to 11 parts per million. The probability of phase transformation from nano-diamond to graphite has been very low and the test experiences are in good agreement with the calculated results. Compared with other synthetic methods, the method of detonation sintered nano-diamond/alumina composites with high temperature, high pressure and short duration has the advantages of operation, environmentally benign and high yields.     

高温法处理铝电解废阴极的机理

高温法是目前国内处理铝电解废阴极的主要研究方向。系统研究了焙烧温度、焙烧时间、样品粒度等对氰化物、氟化物及其它元素脱除效率的作用规律，研究了石墨碎石墨化度、真密度、粉末电阻率与焙烧温度的关系。研究表明，在600℃焙烧时氰化物可以完全分解，在1 000℃以上可以脱除氟及其其它成分(不含碳),氟及其它成分的脱除率主要和焙烧温度有关，焙烧温度越高，氟及其它成分的脱除率越高；石墨碎的石墨化度和真密度随焙烧温度的升高而提高，焙烧温度达到2 600℃时石墨碎的石墨化度达到98.4%、真密度达到2.270 3 g/cm³;石墨碎的粉末电阻率随焙烧温度的升高而降低；焙烧所得石墨碎具有较高的应用价值。     

The superlattice structure and self-adaptive performance of C–Ti/MoS2 composite coatings

To improve the self-adaptability of MoS₂ coating in different environments, the coatings were doped with functional C and Ti by unbalanced magnetron sputtering system. The clear superlattice structure with minimal modulation period was investigated by High Resolution Transmission Electron Microscope (HRTEM). The co-doped coatings have better mechanical properties due to the special structure and the formation of C–Mo, Ti–S and Ti–O bonds, and better lubrication performance in both high humidity and vacuum than those of the single-doped ones. The doped Ti not only facilitates the formation of the MoS₂ (002) basal plane, but also improves the oxidation resistance of the composite film. The degree of friction-induced graphitization on the wear tracks and the quality of transfer films on the wear scars are key factors affecting the lubrication performance of the composite film. In the high-humidity environment, the reasonable doping elements can promote the formation the high-quality transfer film by interacting with H₂O water molecules, which will benefit the lubrication of the coating better. Our findings deepen the understanding of MoS₂ composite coating and provide a new solution for improving the self-adaptability of the coating.     

石墨化竹炭的微观结构及其复合材料的制备与性能

采用SEM及XRD技术表征经2 800℃石墨化处理的竹炭的微观结构;以石墨化竹炭为导电骨料、酚醛树脂为粘结剂、炭黑为添加剂,采用模压成型法制备石墨化竹炭/酚醛树脂复合材料;考察石墨化竹炭的粒度、酚醛树脂用量、炭黑添加方式和用量、成型压力及固化温度等工艺因素对复合材料性能的影响。结果表明:增大竹炭粉粒的粒径、增加炭黑用量和提高固化温度有利于提高复合材料的导电性,但会不同程度地影响复合材料的力学性能、显气孔率和吸水率;随着酚醛树脂用量的增加,复合材料的抗弯强度提高,导电性、吸水率和显气孔率下降;提高成型压力可同时提高复合材料的性能;制备竹炭/酚醛树脂复合材料的最佳工艺条件为竹炭粒度≤75μm、树脂用量30%(质量分数)、炭黑用量5%(质量分数)、成型压力280 MPa、固化温度180℃。     

球墨铸铁加热过程中渗碳体石墨化的原位观察

采用激光共聚焦扫描显微镜直接观察了球墨铸铁在加热过程中渗碳体的分解和石墨形态的演化。结果表明：球墨铸铁在加热过程中渗碳体逐渐溶解,加热速率越快,渗碳体的分解速率越快。加热过程中石墨形态的演变行为与加热速率有关。加热速率较慢,组织中出现了小石墨,原有石墨长大。加热速率较快,渗碳体周围的小石墨逐渐溶解变小。     

外加磁场下C／C复合材料的Fe—Ni催化石墨化以及性能研究

在Fe—Ni存在下,外加磁场不但可以提高酚醛树脂炭的石墨化度而且对新生成的石墨层也具有很好的导向作用。实验以短切雕N基碳纤维为增强体,酚醛树脂为基体碳源,采用液相浸渍的方法制备c／c复合材料。主要研究了外加磁场对c／c复合材料的Fe—Ni催化石墨化、电性能和力学性能的影响。结果表明,磁场作用下对含有铁磁性催化剂Fe—Ni的C／C复合材料的石墨化具有较好的改善作用;C／C复合材料的石墨化度越高其电阻率越低,并且电阻率在不同的磁场方向上呈现出了显著的差异性,平行于磁场方向上比垂直方向上的电阻率更低;但是,随着复合材料石墨化度的提高其抗压强度发生显著的降低。     

Fe2O3对聚芳基乙炔树脂石墨化的影响研究

用不同催化剂催化聚芳基乙炔树脂石墨化,重点研究了Fe2O3含量和热处理温度对PAA石墨化的影响。通过XRD、Raman、SEM和HRTEM分析了PAA热处理温前后的结构和形貌变化。实验结果显示：Fe2O3在热处理过程中转换成铁单质,有效地促进了PAA树脂的石墨化;Fe203含量的增加和热处理温度的升高均可促使石墨结构形...