Hong-fang Sun

Investigation of the Carbon Corrosion Process for Polymer Electrolyte Fuel Cells Using a Rotating Disk Electrode Technique

The carbon corrosion process of low surface area Pt/XC72 and high surface area Pt/BP2000 was investigated using an accelerated durability testing method under simulated fuel cell conditions (a rotating disk electrode approach). A steam etching experiment was also carried out for further understanding of the carbon corrosion process for XC72 and BP2000. It was observed that different carbon corrosion processes resulted in different performance (electrochemical active surface area, mass activity, and double layer capacity) decays of catalysts. The corrosion process was studied using transmission electron microscopy. In Pt/XC72, major corrosion occurred at the center of the Pt/XC72 particle, with some minor corrosion on the surface of the carbon particle removing some amorphously structured carbon black filaments, whereas in Pt/BP2000, the corrosion started on the surface.

Structural Modification of Graphene Sheets to Create a Dense Network of Defect Sites

Pt/graphene composites were synthesized by loading platinum nanoparticles onto graphene and etched at 1000 °C in a hydrogen atmosphere. This results in the formation of a dense array of nanostructured defect sites in the graphene, including trenches, nanoribbons, islands, and holes. These defect sites result in an increase in the number of unsaturated carbon atoms and, consequently, enhance the interaction of the CO2 molecules with the etched graphene. This leads to a high capacity for storing CO2; 1 g of the etched samples can store up to 76.3 cm(3) of CO2 at 273 K under ambient pressure.

Irradiation Damage of Nano-C2S Particles Studied by In-Situ Transmission Electron Microscopy

Development of a reactive nanocement is a new approach to improve the physical and chemical properties of construction materials. However, due to the decreased size of cement particles, beam damage during transmission electron microscope (TEM) observation becomes more severe than in conventional cement. In this work, irradiation damage to nano-C2S (dicalcium silicate) is observed and studied by in-situ evolution of diffraction patterns (DP), high resolution TEM (HRTEM), and electron energy-loss spectroscopy (EELS). The results show that the damage to nano-C2S occurs through a decomposition reaction. Nano-C2S is first amorphized, and then re-crystallized into CaO nano-crystals with average size of 7 nm surrounded by an amorphous matrix of Si and SiO2. During this process, C2S particles exhibit volume shrinkage. The damage energy causing the reaction was analyzed and electron-electron inelastic scattering produced radiolysis and heat, leading to the observed phenomena.

Enhancing the Catalytic Performance of Pt/C Catalysts Using Steam-Etched Carbon Blacks as a Catalyst Support

XC-72 carbon blacks were etched using steam for different times and used as a catalysts support for oxygen reduction reactions. Transmission electron microscopy (TEM) results show that the center parts of the XC-72 were more easily etched away. X-ray diffraction shows that the 002 and 10 peaks of the XC-72-based samples are initially sharp, but then broaden during the corrosion process. TEM shows that the steam etching can improve the Pt dispersion uniformity on the surface of the support and decrease the Pt particle size. Electrochemical characterization shows that the mass activity of a sample etched for 1h was better than that of the unetched samples and a commercial catalyst. The electrochemically active surface area of the samples was also significantly increased after etching. Steam etching is a simple and efficient method to increase the performance of the fuel cells catalysts.