Preparation Of Nitrogen-doped Carbon Materials Based On Polyaniline Fiber And Their Oxygen Reduction Properties

Fuel cell is a kind of device which can convert chemical energy of a fuel into electrical energy directly.It is highly efficient and environmentally friendly,known as "21st Century Energy Star".At present,fuel cell has not yet achieved large-scale commercialization.Because the most commonly used catalyst for cathode oxygen reduction reaction is Pt-based catalyst,and Pt is expensive,which seriously limits the development of fuel cells.Therefore,the preparation of cathode oxygen reduction catalyst which can replace Pt and have low cost,high activity,good stability,is the key to the development of fuel cell.In recent years,nitrogen-doped carbon materials have gained extensive attention due to their low price,excellent oxygen reduction activity,good resistance to methanol and high stability.In this paper,polyaniline was used as the main raw material,and the nitrogen-doped carbon material were prepared by different methods.The morphology,composition and structure of the materials were analyzed by various methods.The oxygen reduction performance was also studied.The main contents and results are as follows:(1)Nitrogen-doped carbon material was prepared by high temperature carbonation with the raw materia of polyaniline.The prepared material was spherical with an average diameter of 2?m,and the twining fibers were clearly seen by transmission electron microscopy.The effect of carbonization temperature on the ORR performance of the material was studied.The results show that when the carbonization temperature is 900?,the prepared carbon material(CSDP-900)has the best ORR performance.The onset potential is-0.06 V,which is almost the same as that of the commercial Pt/C catalyst.The limit current density is 6.4 mA·cm-2,which is 1.9 mA·cm-2 higher than that of Pt/C catalyst.The electron transfer number of CSDP-900 sample is 4.3 which was calculated by the KL equation.(2)Polyaniline and glucose were used as raw materials to prepare porous nitrogen-doped carbon materials by hydrothermal and high temperature carbonization activation.Among them,the sample(PCPG-900)prepared at the carbonization temperature of 900? has the best oxygen reduction reaction(ORR)performance.PCPG-900 shows a porous shape with a specific surface area of 1788 m2·g-1 and an average pore size of 2.25 nm.The results show that the onset potential of PCPG-900 sample is-0.171 V in the 0.1 M KOH solution at 1600rpm,close to commercial Pt/C catalyst(-0.03 V).The limit current density is 5.4 mA·cm-2,which is about 0.9 mA·cm-2 higher than that of Pt/C catalyst(4.5 mA·cm-2).In the range of-1.4 V to-0.8 V,the average electron transfer number is 4.2,indicating that the reaction is direct 4 electronic reaction.The PCPG-900 sample has better resistance to methanol and stability than commercial Pt/C catalysts.(3)Flaky nitrogen-doped carbon material was synthesized by hydrothermal method with the raw materials of polyaniline and graphene.It is proved that polyaniline is combined with graphene by a variety of characterization means.The result shows that the sample with the ratio of polyaniline and graphene to 4(HP-GH-4)has the best oxygen reduction activity.The onset potential of HP-GH-4 is-0.13 V,which is slightly negative compared with Pt/C catalyst.The limit current density is 6.5 mA·cm-2,2 mA·cm-2 higher than commercial Pt/C catalyst.The electron transfer number is 4.1,proving that the reaction is a direct 4-electron reaction.