Nitrogen-self-doped Non-noble Metal Catalysts Derived From Polyaniline And Biomass Materials For Low Temperature Fuel Cells

Low temperature fuel cells(LTFCs) have been greatly concerned because of their many advantages such as high efficiency, low emission, quiet, and wide source of fuel. However, the commercialization of LTFCs has still been heavily hampered by the utilization of expensive Pt-based noble metal electrocatalysts for oxygen reduction reaction(ORR). Therefore, the development of low cost and highly active non-noble metal electrocatalysts for ORR to substitute Pt-based catalysts is very important for the commercialization of fuel cells. Meanwhile, it has important scientific significance and application value. Among all the non-noble metal catalysts, doped carbon materials have been widely studied for their high catalytic activities, excellent stabilities and excellent CO and methanol poisoning resistances. In this thesis, nitrogen doped carbon based materials for oxygen reduction with unique morphology have been prepared by in situ polymerization of aniline, urea composite with polyaniline, using cheap and abundant natural biological resources for the preparation of the catalyst precursor.First, we synthesized the polyaniline derived precursor using ferric chloride both as an oxidant to polymerize aniline and an iron source for the non-noble metal catalysts(NNMCs). After pyrolysis of the precursor at a sharp heating rate and chemical post-treatment, the product owns a larger number of nano-pore structures and high surface area up to 432 m2·g- 1. The electrochemical characterization demonstrates that the prepared catalyst not only has a four-electron transfer pathway like the Pt/C catalyst, a high onset and halfwave potential(E0= 0.91 V, E1/2= 0.81 V(vs. RHE)), but also possesses a better electrochemical stability than that of Pt/C under acid medium. In addition, such catalyst shows an outperformed ORR activity than Pt/C in alkaline media. This can be caused by its graphitized carbon with high surface area and unique porous structures, as well as the high content of pyridinic nitrogen and graphitic nitrogen.Second, nitrogen-doped carbon catalyst with a porous graphene-like structure is prepared by pyrolyzing the polyaniline with addition of urea. Herein, the urea not only severs as a nitrogen source similar to polyaniline by incorporating nitrogen atoms into carbon matrix, but plays a key role in forming the porous graphene-like structure carbon nanosheet. The electrochemical characterization shows the prepared catalyst with a unique graphene-like structure possesses an outperformed oxygen reduction reaction(ORR) activity than that of the commercial Pt/C catalyst in alkaline media. It shows a nearly 30 mV positive shift of the half-wave potential to compare with Pt/C, and a higher stability than Pt/C in alkaline medium. Significantly, such catalyst also exhibits a good ORR activity which is comparable to Pt/C, as well as a higher stability than Pt/C in acidic media. The improved ORR activity can be comprehensively attributed to the increased active nitrogen content, edge defects, surface area and the porous structure. In addition, such thin films consisted of graphene-like carbon nanosheets can provide a fast electron pathway and benefits the transformation of ORR related species, which also facilitate ORR activities.Third, we demonstrate a facile and green strategy to synthesize a novel nitrogen-doped carbon nanoporous material with high surface area using pork liver both as a nitrogen and carbon source. After adding a small amount of iron into pork liver, and then cooked, dried carbonized and followed by post treatments including ball milling, acid leaching and the second heat treatment, the CPL-Fe(derive from pork liver and iron) catalyst can be obtained. The prepared catalyst owns a larger number of structural nano-pores and high surface area due to the expansion nature of biomass materials at high temperature. The onset potential and half-wave potential of this catalyst is up to 0.94 and 0.79 V(vs. RHE), respectively, which very comparable that of the commercial Pt/C catalyst. In addition, such catalyst shows a good stability and immunity for methanol crossover and CO poisoning than that of Pt/C.Forth, a pig blood-derived nitrigen-doped carbon catalyst is successfully fabricated with aid of metal iron in the synthetic process. Compare to CPL-Fe catalyst, such pig blood-derived(CPB-Fe) catalyst not only has high surface area and outstanding nano pores, but also possesses a higher ORR activity due to the abundant hemoglobin in the precursor. The onset potential and half-wave potential of CPB-Fe is up to-0.04 V and-0.16 V(vs. SCE), respectively, which approach to the commercial Pt/C catalyst(E0 =-0.03 V, E1/2 =-0.14 V). Similarly, such catalyst also shows a superior stability and fuel(methanol and CO) tolerance than Pt/C catalyst.Finally, we demonstrate a green synthesis route of nitrogen-doped carbon materials by using eggs as nitrogen sources combining with iron sources and multi-walled carbon nanotubes(MWNTs). After carbonized and post treatments, the obtained hybrid(CE-Fe-MWNT) catalyst shows the highest surface area(680 m2·g-1) and excellent porous structure as same as the prepared CPL-Fe and CPB-Fe catalyst. Here the highly graphitized MWNTs provide a fast electron transfer pathway for ORR, improving the catalytic activity and stability. Such catalyst has a four-electron transfer pathway like the Pt/C catalyst, and the onset potential is only 20 mV lower than Pt/C. such catalyst is insensitive to CO and methanol poisoning, shows a good catalytic selectivity.