Preparation And Electrocalalytic Properties Of The Fuel Cell Cathode Catalyst

The fuel cell is one of the new energy technologies to partially or completely replace tranditional fossil energy. Yet, Reaction kinetic of oxygen reduction reaction (ORR) at cathode electrode is much slow compared to the oxidation reaction at the anode electrode and then high performance electrocatalysts are required to promote the ORR. Pt-based catalysts remain the best one for the ORR due to the activity and the electrochemical stability. However, Pt metal is one of the rarest and the most expensive metals in the earth’s crust and then the high cost from Pt-based catalysts seriously hinders the commercialization of fuel cells. Therefore, it is an important issue to explore non precious metal electrocatalysts towards the ORR for fuel cells.In this work, based on the excellent conductivity of reduced graphene oxide (RGO) and the promising electrocatalytic performance of Co- and Mn-based electrocatalysts in alkaline medium, a series of RGO supported non-precious metal electrocatalyst composites were prepared by a template of layered double hydroxides (LDH). The composition, structure, morphology, and electrocatalytic performance of the materials are characterized by various techniques. The work of this thesis are as follows: (1) Reduced graphene oxide supported cobalt and manganese compound metal hydroxide composite precursor (Co3Mn-LDH/RGO) was prepared by coprecipitation method, through calcinating precursor Co3Mn-LDH/RGO at a certain temperature 550℃, reduced graphene oxide supported composite metal oxide cathode materials (CoO/MnO2/RGO) was prepared. After the analysis of XRD, SEM, TEM and XPS, it showed that CoO and amorphous MnO2 nanoparticles were uniformly dispersed in the carrier of reduced graphene oxide; electrical test results showed that the catalytic performance, the preparation of CoO/MnO2/RGO catalyst is obviously better than that of CoO/RGO, MnO2/RGO and physical mixture of catalyst that the proportion is same, it compared the commercial Pt/C catalyst for oxygen reduction catalytic activity, selectivity and also higher electrochemical stability. The half wave potential of oxygen reduction reaction of the composite catalyst in 0.1 M KOH electrolyte is 0.78 V vs. RHE,0.90 V vs. RHE is the initial potential, and it was almost completely immune to methanol, the stability of 18000 s by i-t polarographic test show 5% better than the commercial Pt/C.(2) Nitrogen doped reduced graphene oxide surpported tricoponent layered double hydroxides (CoNiFe-LDH/N-RGO), the main layer of which contained cobalt, nickel and iron, was prepared by coprecipitation method. secondly, Co/NiO/Fe2O3/N-RGO catalytic materials was prepared by roasting the precursor CoNiFe-LDH/N-RGO. XRD, XPS, SEM, TEM and other means of analysis shows that the structure of the precursor has a typical layered structure. LDHs laminate collapsed at 750 degree and metal Co, amorphous NiO and amorphous Fe2O3 nanoparticles was achived; the electro catalytic performance tests showed, Co/N-RGO target of the catalyst has high catalytic activity for oxygen reduction reaction (ORR) and NiO/Fe2O3/N-RGO has good electrochemical activity for oxygen evolution reaction (OER), the catalyst showed dual function contained excellent properties for oxygen reduction and oxygen evolution, has a good application prospect. The Co/NiO/Fe2O3/N-RGO composite catalyst for Oxygen Reduction Reaction test, has a good current density output and 4e reaction rout.The half wave potential of catalyst is 0.803V, and catalyst also showed good Oxygen Evolution Reaction (OER) activity, the current density output is high, the initial potential is 1.51V, only lower 20mV than the commercial Pt/C.