Preparation Of Novel Fe/N/C Catalyst And Its Application In Oxygen Reduction Reaction For Fuel Cells

Fuel cells are considered as one of the most promising power source candidate in future, because they have some obvious advantages such as high energy density, high overall energy conversion efficiency, clean fuel using and low emissions. The cathodic oxygen reduction reaction (ORR) plays a crucial role in full cells. The rapid development of these applications calls for increasing demands for the improvement of ORR. Although Pt-based electrocatalysts are still the most efficient and active materials for ORR, their disadvantages such as high cost, sluggish electron transfer kinetics in alkaline solution hinder their widespread commercialization. Recently, the non-precious electrocatalysts such as nitrogen-doped carbon materials and Fe/N/C materials are widely explored as the alternatives to Pt-based catalysts. Some novel micro-porous carbon-supported iron-based catalyst is comparable to the Pt-based materials. In this article, our goal is to synthesize the novel Fe/N/C and derived materials with high ORR catalytic properties.In this article, we use graphene as the carbon source due to its unique morphology, high surface area, good electrical conductivity and flexible surface functionalization chemistry. Firstly, we synthesized the graphene oxide (GO) with the modified hummers method, and then prepared the polypyrrole/graphene oxide (Ppy/GO) and sulfourea/graphene oxide (Sulfourea/GO) to improve their ORR catalytic properties by doping N atoms or S atoms respectively. All of these three materials (GO, Ppy/GO and Sulfourea/GO) keep well sheet morphology and have ORR catalytic properties. Through electrochemical catalytic properties testing, we suppose that the GO has ORR catalytic properties with the onset potential of -0.25 V (vs SCE), cathodic potential of -0.38 V (vs SCE). The Ppy/GO have the best ORR catalytic properties in GO, sulfourea/GO and Ppy/GO with the onset potential of -0.21 V (vs SCE), cathodic potential of -0.35 V (vs SCE). The nitrogen-doped processing may be useful to improve carbon materials" ORR catalytic properties.Advantages in low cost, and excellent catalytic activity of Fe/N/C render them to be one of the excellent ORR electrocatalysts. Here, Fe2O3/polypyrrole/graphene oxide (Fe2O3/Ppy/GO) with the Fe2O3 embedded in the Ppy modified GO are synthesized using hydrothermal method. With an optimal iron atom content ratio of 1.6% in graphene oxide and heat treatment at 800?, the Fe2O3/Ppy/GO-800 exhibited enhanced catalytic performance for ORR with the onset potential of -0.1 V (vs SCE), cathodic potential of -0.24 V (vs SCE), an approximate 4e" transfer process (3.7) in O2-saturated 0.1 M KOH, and superior stability that only reduced 5% catalytic activity after 5000 cycles. The decisive factors in improving the electrocatalytic and durable performance are the intimate and large contact interfaces between nanocrystallines of Fe2O3 and Ppy/GO, in addition to the high electron withdrawing/storing ability and the high conductivity of GO doped with nitrogen from Ppy during the hydrothermal reaction. The Fe2O3/Ppy/GO showed significantly improved ORR properties and indicated that Fe-N-C electrocatalysts played key role in fuel cells.Furthermore, we synthesized Co3O4/polypyrrole/graphene oxide (Co3O4/Ppy/GO) and CoxFeyOz/polypyrrole/graphene oxide (CoxFeyOz/Ppy/GO) using a similar hydrothermal method, and investigated their ORR catalytic properties. Comparing the ORR catalytic properties of the samples, we conclude that Fe2O3/Ppy/GO have better catalytic properties than Co3O4/Ppy/GO and CoxFeyOz/Ppy/GO. Iron-doped carbon materials have more ORR catalytic sites than cobalt-doped carbon materials. The Co3O4/Ppy/GO still have good ORR catalytic properties with the onset potential of-0.21 V (vs SCE), cathodic potential of -0.31 V (vs SCE), which are better than Ppy/GO. The onset potential and cathodic potential of Co3O4/Ppy/GO-800 after heat treatment at 800? can reach -0.18 V and -0.27 V.In conclusion, novel non-precious metal doping and nitrogen doping GO electrocatalysts were prepared using hydrothermal method and their electrochemical activities were investigated. Fe2O3/Ppy/GO can be used as one efficient Fe/N/C catalyst for ORR. Fe (or Co) coupled on nitrogen-doped GO structure leaves as a potential catalyst for oxygen reduction reaction in alkaline media.