Synthesis Of Cobalt Compound/graphene Composite And Their Electrocatalytic Activities For Oxygen Reduction Reaction

Direct methanol fuel cell(DMFC)is a new energy conversion technology,which has many advantages such as environmental friendliness,high energy conversion rate,rich fuel and no noise pollution.It also has potential in fuel cell electric vehicle and energy field.At present,the main technical bottleneck of the DMFC is the slow kinetics of the cathodic oxygen reduction reaction(ORR),and the platinum(Pt)based noble metal catalyst,which needs far greater than the anode.However,the shortage of Pt resources,high price and easy poisoning limit the large-scale use of DMFC.Therefore,research and development of cathodic non noble metal catalysts with abundant resources,low cost,high catalytic activity,high durability and excellent methanol resistance will effectively promote the commercialization of DMFC.Carbon based catalysts have been widely studied because of their good catalytic performance in ORR,good stability and the ability to resist methanol.Among them,graphene based non noble metal(NNM)catalysts have become one of the most important topics in the field of fuel cell due to its high specific surface area(SSA)and excellent conductivity.This dissertation through the methods such as the non metal heteroatom dual-doping,transition metal phosphide composite,and supported transition metal nanoparticles to design and prepare a series of excellent properties of graphene based ORR catalysts,and the main achievements include:(1)Using graphene oxide(GO)and thiourea as precursors,a three dimensional networks N,S-rGO was prepared by one-step low temperature hydrothermal reaction.The catalyst had a high content of N and S(2.1 at%,3.54 at%),and contained a high proportion of thiophene sulfur(C-S-C),and a high percentage of pyridinic-N(44.6%)and graphitic-N(33.9%).The N,S-rGO-18h had good ORR catalytic performance in alkaline solution,which through the four electron pathway with high efficiency,and it also had high catalytic stability and methanol resistance which were much better than that of Pt/C.(2)Using GO,cobalt nitrate,urea and ammonium fluoride as the precursors,the graphene composite cobalt precursor was obtained by hydrothermal reaction,then the cobalt phosphide graphene microflowers composite materials(rGO@CoP)was prepared under the protection of argon and reaction with hypophosphite in middle temperature.The electron transfer number of rGO@CoP in alkaline solution was increased from 2.19 to 3.66,compared to the uncomplexed CoP,and the activity of it had greatly improved than that of pure CoP.Although there was a certain gap between it and the commercial Pt/C,but its stability and methanol tolerance were much better than that of Pt/C,which provided a reference for further exploration of transition metal phosphide composite material applied in ORR.(3)Using xylitol,GO,melamine,cetrimonium bromide(CTAB)and cobalt chloride as precursors,the cobalt compounded N-doped carbon precursor was obtained by hydrothermal reaction,then the Co-N-C composite was synthesized through 800 ? pyrolysis under the protection of argon,finally the thin-slice like four oxidation three cobalt compounded N-doped graphene composite(Co3O4-N-Gr)was prepared through sulfuric acid activation.The N content of the catalyst was 4 at%,and in alkaline solution,its ORR onset potential and half-wave potential were both positively than that of Pt/C,and the limiting current density is as high as 5.4 mA cm-2.Moreover,it had excellent stability and excellent methanol tolerance,and its ORR was highly efficient through four electron pathways.