Synthesis Of N-doped Carbon Materials Support Palladium-based Electrocatalysts And Its Performance Investigation

Fuel cells, which directly convert the chemical energy to electric energy by electrochemical reactions, have received considerable attention mainly due to their environmental friendliness. However, the commercial application of the DAFCs is still hindered by several issues including its insufficient activity and high cost of anode catalysts. Therefore, many efforts have been made to improve the utilize ratio of catalysts and maximize the utilization of the catalysts to reduce the cost. On the one hand, optimized the microstructure and surface properties of metal catalysts, and improve its catalytic activity。On the other hand, the utilization of the electrocatalysts is strongly related to the supports. N-doping of the support is generally important to immobilize metal nanoparticles on the support, produce some active Me-N sites, and generate good electrocatalytic activity and stability. To solve these problems, we synthnesed Pd-based catalysts supported by N doped carbon materials and the effects of the doping characteristic about the structure and electrocatalytic activity of catalysts.In this paper we synthesized the N-MWCNTs, NG and hollow Co-N-CMs three kinds of nitrogen doped carbon materials. And the nitrogen doped carbon materials were used as supports for synthesizing different microstructure Pd-basd nanocrystals, respectively. We studied the influence of different supports for palladium nanocrystal about morphology, particle size and electric catalytic properties, and discussed its influence laws. The main content of this paper has the following several aspects:Firstly, not only the current research of low temperature fuel cell, the progress of catalyst and catalytic mechanism were given, but also the current questions about the fuel cell catalyst, objective and the main research contents of this paper were described in detail.Secondly, a two-step strategy was employed to preparation N-doped multi-walled carbon nanotubes(N-MWCNTs) supported hollow Pd Cu alloyed nanocubes catalyst(H-Pd Cu/N-MWCNTs), which included the synthesis of N-MWCNTs using polypyrrole(ppy) as the source of nitrogen and the preparation of the hollow Pd Cu alloyed nanocubes. According to transmission electron microscopy(TEM) measurements, the as-prepared hollow Pd Cu alloyed nanocubes catalyst has superior dispersibility, and the average diameter is about 50 nm. XPS measurements reveal that N atoms have been doped in MWCNTs, and there are abundance of pyridinic N and graphitic N species on N-MWCNTs surface. The electrochemical measurements indicate that the hollow Pd Cu alloyed nanocubes catalyst has a better electrocatalytic activity and stability for the alcohols oxidation.Thirdly, a series of N doped graphenes using polypyrrole(ppy), melamine and polyaniline(PANI) as the source of nitrogen, respectively. Hollow Pd Cu alloy nanocubes catalysts supported by N doped graphene(H-Pd Cu/NG) were successfully prepared by a one-pot template-free method. The influence of the different N species(pyridinic N, pyrrolic N and graphite N) on the morphologies and electrical properties of H-Pd Cu was studied. The catalysts were characterized by transmission electron microscopy(TEM), field emission scanning electron microscopy(FESEM), X-Ray Diffraction(XRD), elemental mapping and X-ray photoelectron spectroscopy(XPS). The results indicated that the prepared H-Pd Cu(about 50 nm) supported by N doped few layer graphenes without aggregation and the N atoms are also distribution in graphenes homogeneously. The different N source provides different N species, which enhanced the activity of the catalysts. Electrochemical characterizations reveal that the H-Pd Cu/NG catalysts have excellent catalytic activity and stability toward alcohols oxidation in alkaline electrolyte, which can serve as promising anode catalysts in direct alcohols fuel cells(DAFC).Fourthly, N-doped graphenes supported Pt-Pd Cu nanoparticles as catalysts for ethanol electrooxidation. The N-doped graphene were synthesized using EDTA and melamine as the N source, and supported Pt decorating Pd Cu nanoparticles. According to the different characterization tests, the Pt-Pd Cu nanoparticles are well-dispersed on the surface of the NG support. And the electrochemical measurements show that the catalysts exhibit enhanced electrocatalytic activities and stability. Because of these results, the as-prepared Pt-Pd Cu/NG catalyst might be an economically viable alternative for methanol oxidation.Fifthly, cobalt, nitrogen–codoped carbon materials with special morphology supported Pd catalyst(Pd/Co–N–CMs) for alcohols electrooxidation. Melamine was used as nitrogen source, formaldehyde as carbon source and cobalt acetate as metal precursor to synthesized nitrogen–codoped carbon(Co–N–CMs) without a template. The Pd catalysts were supported by Co–N–CMs. Results show that the Co–N–CMs has larger specific surface area, the Pd nanocrystals loding on the surface of Co–N–CMs with good dispersion, and shows a stronger cooperative catalytic effect.