Study Of Carbon Materials As Catalysts For Fuel Cell

With the rapid social economics development, we are faced with the deterioration of the natural environment and the threat of depletion of natural resources, and how to make the best use of resources and energy, relieve of environmental impact, becoming a pressing issue. Proton exchange membrane fuel cell(PEMFC) system attracted everyone for its’ unique structure, environment-friendly, fast start, no electrolyte loss, long life, higher power density and energy density advantages. However, the fuel cell electrode reaction kinetics of the process is slow, requires an efficient catalyst to ensure efficiency of the whole system. The best performance, the most widely used fuel cell catalyst remains platinum based catalysts, but the platinum price is extremely expensive, it costs too much if we develop large-scale commercial applications, in addition, Pt based catalysts are easy poisoned, the problem of higher oxygen reduction overpotential cannot be fully resolved. Thus the development of low-cost, efficient, stable fuel cell catalysts has become an urgent task of proton exchange membrane fuel cell development.Based on a review of the latest research progress in current PEMFC catalyst, we used different precursors to prepare several N, P, S hetero atom doped carbon material, in order to break the electric neutrality of carbon material, cause structural defects, so that the carbon material can turn into an excellent oxygen reduction catalyst. The composition and surface state analysis, microscopic texture characterization and electrochemical synthesis of catalysts were adopted to systematically investigate the doped hetero atoms, doped structure-activity type, structure of the carbon material and other electrically between the catalytic activity relations; we also adopted theoretical calculations to explore the mechanism of catalytic oxygen reduction behavior. Based on the carbon materials, further research was did, we prepared grapheme-like carbon material with porous structure by template method, and as a catalyst supporter, we synthesized Pt / C, the feasibility of ethanol oxidation catalyst was carried out. The main contents of this paper are as follows:1) The oxygen reduction reaction(ORR) at the cathode plays a key role in controlling the performance of fuel cell, and the efficient ORR electrocatalysts are essential for practical applications of the fuel cells. Currently, Pt-based electrocatalysts with the best performance are widely used in fuel cells, but Pt is very expensive. The introduction of various heteroatom(N, P, S) into graphene has a great effect on the ORR activity of samples prepared by thermal decomposition in this study. In order to understand the discrepant ORR activity of the doped graphene-based catalysts, electrochemical experiments and theoretical calculation were performed. According to the results and analysis, it is proposed that heteroatom doping alters the surface state of graphene materials. Different adsorption energy between O2 molecule and heteroatom doped graphene are produced as a result, which alters the bond distance of O2 molecule. The obtained results can be used for designing and developing new and suitable electrocatalysts for ORR in the future.2) A Low-cost, high-performance and durable catalyst for oxygen reduction reaction(ORR) is prerequisite for the commercialization of fuel cells. Continuous efforts are made to explore nonprecious, efficient catalysts to replace the expensive and scare platinumbased catalysts. Here we demonstrate a kind of novel nitrogen and phosphorus co-doped mesoporous carbon spheres(NPMCS) synthesized by hydrothermal assisting pyrolysis of food yeast. The as-prepared mesoporous carbon hollow spheres exhibit a high specific surface area of 1223 m~2/g, deliver an excellent electrocatalytic performance for ORR in alkaline media, superior durability and high resistance to methanol cross-over effect.3) The catalyst supporter is a vital part of catalyst, we used calcium carbonate as a template, leaf extract as raw material, synthesized a class of multi-layered graphene-like material which has a porous structure, it was found that with decreasing heating rate, the resulting materials’ surface area becomes larger. At 2℃/ min, the material has a specific surface area of up to 1337 m~2 / g, which is suitable for supporting Pt catalyst, the results show that the catalyst obtained has a high ethanol oxidation current density, which is 2.8 times bigger than commercial platinum catalyst. we inferred its outstanding performance not only thanks to supporter’s large specific surface area, but also doped nitrogen and sulfur atoms, this unique composition and structure of the material can further improve catalytic activity, meanwhile the catalyst can promote the oxidation of carbon monoxide, which can efficiently prevent catalyst from being poisoned.