Preparation And Oxygen Reduction Performances Of Heteroatom-Doped Carbon Materials

As a new energy, low-temperature fuel cell are very promising energy conversion devices for future sustainable and distributed energy generation both for mobile, portable and stationary applications because of their high efficiency and low pollution emission. Because the cathode oxygen reduction process is very slow and requires high loading on the cathode to accelerate the reaction process. Currently, platinum-based catalysts have been considered as the most effective electrocatalysts for ORR in fuel cells However, the main issues preventing mass-scale commercialization are the cost and durability that are not meeting worldwide requirements. Compared to all metals cathodic catalysts, Non-metal-doped carbon materials have unique ORR activity, such as long-term operation stability, tolerance for CO and methanol cross-over. In this thesis, we have been prepared with high activity and low-cost non-metallic heteroatom-doped carbon material as a fuel cell catalyst Combined with its morphology, chemical structure, electrochemical activity and other parameters on the materials, theoxygen reduction mechanism and its influencing factors(1) Based on the unique electronic properties and high surface area of carbon nanotubes as well as the similar electronegativity of sulfur and carbon, a novel electrocatalyst for the oxygen reduction reaction(ORR) was fabricated by directly annealing oxidized carbon nanotubes and benzenedithiol in nitrogen. Through the use benzenedithiol isomers as sulphur source, change the annealing temperatures, chang the CNTs/BDT mass ratios for get sulfur-doped carbon nanotubes with most excellent electrocatalytic activity. The structural and chemical properties of the resulting sulfur-doped carbon nanotubes(pSCNTs) were investigated using transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The catalytic activity of the pSCNTs towards ORR in alkaline medium was evaluated using rotating ring disk electrode voltammetry. The as-synthesized pSCNT-900(annealed at 900 °C) exhibits excellent electrochemical performance towards ORR with an onset potential of-0.082 V(vs Ag/AgCl), a high kinetic current density of 34.6 mA cm-2 at-0.35 V), a dominant four-electron transfer mechanism(n = 3.71 at-0.35 V), as well as excellent methanol tolerance and durability. The results obtained are significant for the development of S-doped carbon-based catalysts for alkaline fuel cells.(2) Hollow carbon spheres has unique structure and excellent properties, including a low density, and high electrocatalytic electron-deficient elements like boron(electron negativity: 2.04) can break the uniform charge density of the sp2 carbon lattice and thus could potentially induce efficient ORR. PS@PF-B was prepared from boron and PS@PF as raw materials. By hydrothermal reaction,monodisperse HCSs were obtained after this spherical composite(PS@PF-B) annealing in the inert gases at high temperaturet. The structural and chemical properties of the resulting Boron-doped hollow carbon sphere(BHCSs) were investigated using transmission electron microscopy and FTIR spectroscopy. The catalytic activity of the BHCSs towards ORR was evaluated using rotating ring disk electrode voltammetry. The as-synthesized BHCS-900(annealed at 900 °C) exhibits excellent electrochemical performance towards ORR with an onset potential of-0.032 V(vs Ag/AgCl), a high kinetic current density of 83.2 mA cm-2 at-0.35 V), a dominant four-electron transfer mechanism(n = 3.89 at-0.35 V), as well as excellent durability. The results obtained are significant for the development of B-doped carbon-based catalysts for fuel cells.