Carbon Materials Derived From N-rich Amino Acid For Application In ORR

Fuel cells is an efficient and environmentally friendly energy technology that has many merits such as less pollution and high efficiency energy conversion. Oxygen reduction reaction(ORR) on the cathode is the decisive component for various fuel cells, since ORR dominates the overall performance of these energy storage and conversion systems. However, due to the high costs, low stability and limited reserves in the global village of precious metal, involving Pt, Pd, etc., which greatly limits the entire fuel cell commercialization process. Hence, exploring cheap raw materials,simple preparation, highly active and affordable alternative catalysts to Pt-based electrocatalyst has become a research hot.This work is focused on preparation of carbon-based materials and the application in ORR electrocatalysis. The work consists of Synergy between isolated-Fe3O4 nanoparticles and CNx layers derived from lysine, Histidine modified the S-doped matrix composite and Rod-like N-doped graphitic carbon, which served as highly efficient electrocatalyst for ORR. In terms of the prepared non-precious electrocatalyst, a series of physical measurements are conducted to characterize their structure, and many electrochemical tests are employed to evaluate the performance of oxygen reduction reaction, respectively.The thesis consists of three parts as following:Part I: Synergy between isolated-Fe3O4 nanoparticles and CNx layers derived from lysine to improve the catalytic activity for oxygen reduction reactionIn order to seek heterogeneous electrocatalyst with efficient catalytic activity for oxygen reduction reaction(ORR), Fe3O4-CNx composite reported in our previous work was studied as electrocatalyst for ORR but showed poor catalytic activity. To improve the catalytic activity, Fe3O4-CNx composite is modified by the CNx layers derived from lysine through pyrolysis. The physical characterization shows that the coral-shaped morphology of the resultant composite(Fe3O4-CNx-Lys) is still retained,while the degree of its graphitic crystalline increases. Besides, Fe3O4-CNx-Lys displays 364.7 m2 g-1 of surface area with hierarchical porous structure.Electrochemical tests show that the catalytic activity Fe3O4-CNx-Lys for ORR is notonly higher than those Fe3O4-CNx, XC-72-Lys derived from lysine and XC-72 Vulcan carbon but also comparable to that of commercial Pt/C(20 wt%).Part II: Histidine modified the S-doped matrix composite by carbonization for oxygen reduction reactionIn this part, we prepared the S-doped flocculent carbon matrixs by carbonizing sucrose with concentrated sulfuric acid. The prepared carbon matrixs was modified with histidine a type of nitrogen-rich amino acid to form the highly activie heterostructure carbon materials. Through a series of physical tests, involving XRD,TEM and XPS, indicating the heterogeneous structure carbon material possesses a high degree of graphitization, rich pyridine-nitrogen in the surface. Electrochemical tests show that the obtained sample not only shows high performance for oxygen reduction, but also exhibits excellent resistance to methanol poisoning.Part III : Rod-like N-doped graphitic carbon derived from histidine for highly efficient oxygen reduction reactionRod-like N-doped graphitic carbon(SHC-SBA-15) with high surface area is synthesized using SBA-15 as template. Brunauer-Emmett-Teller(BET) surface area of obtained carbon material is ca. 915.3 m2g-1with a pore size distribution centered at ca.4 nm. The half-wave potential of the linear sweep voltammograms curve for SHC-SBA-15 in O2-saturated 0.1 mol L-1 H2SO4 solution is lower than that of commercial Pt/C(20 wt.%), but its onset potential and its limited diffusion current density are almost as same as that of Pt/C in acidic medium. Although the oxygen reduction reaction(ORR) activity of SHC-SBA-15 is lower than that of commercial Pt/C, its low cost, long term-operating durability and excellent CH3 OH tolerance render it as a potential alternative to Pt-based catalysts for ORR.