| With the continuous development of human society,the energy issue is becoming more and more serious and imperative.The development of high-efficient and renewable energy conversion and storage system is a great challenge.In this regard,supercapacitors and fuel cells gain widerspread applications.However,the energy density of supercapacitors still remains a low level,which greatly limits the scope of its application.For fuel cells,it depends on the large cost of precious metal Pt to catalyze the oxygen reduction reaction of cathode.However,the scarity and high cost of platinum hindered the large-scale commercial application of the fuel cell.Therefore,it is imperative to develop high energy density electrode materials for supercapacitors and an alternative of low-cost and non-nobel meal catalyst for fuel cell cathode oxidation.Porous carbon materials have rich pore structure,large specific surface area and excellent stability.These excellent properties are suitable for adsorption and separation,catalysis and electrochemistry.Different pore structures and chemical composition surface properties significantly affect the properties of capacitance and catalytic of oxygen reduction.In our experiments,a simple hydrothermal method was developed to prepare spherical,fibrous carbon materials,which were used as electrode materials for supercapacitors.Based on the method for synthesizing carbon fibre,iron atoms were in-situ doped with the introduction of Fe(Ac Ac)3 in short rodlike carbon material,and its catalytic activity for oxygen reduction was studied.The specific research contents and conclusions include the following aspects:1.Synthesis of nitrogen-doped carbon nanospheres and their properties in supercapacitors.Homogeneous nanoparticles were synthesized by hydrothermal method,using phenol and formaldehyde as raw materials with the aid of surfactant and catalyst.By changing the amount of phenol and formaldehyde or selecting different surfactants,the particle size of phenolic resin-based polymers or carbon nanoparticles calcined at high temperature can be accurately controlled.The morphology,structure and electrochemical properties of activated carbon nanospheres with different diameters were studied.Among them,the carbon nanosphere(NCSA-OTAB)with the particle size of 86 nm demonstrates the best electrochemical performance with the specific capacitance is 247 F g-1 in the three electrode system,allowing for its specific surface area up to 1462 m2 g-1 and hierarchical pore structure.Also,in a two-electrode system,the energy density is up to 6.74 Wh kg-1(0.1 A g-1)with low resistance and good cyclic stability.2.Preparation of nitrogen-doped carbon nanofibers and their properties in supercapacitors.Nano-fibers with high aspect ratio were synthesized by hydrothermal method using phenol,formaldehyde,benzimidazole(N source)as raw materials under the action of surfactant cetyltrimethylammonium bromide(CTAB).This kind of one-dimensional carbon material with high aspect ratio provides large specific surface area and fast ion transport channel,which holds great pomise for super capacitance.After calcination at high temperature and activation with KOH,the diameter of carbon nanofibers is about 45 nm together with high specific surface area up to 1814.4 m2 g-1.Furthermore,the electrochemical performance of carbon fibers as electrode materials is investigated.Experimental results denmonstrate that electrode material composed of carbon nanofibres affords the specific capacitance of 267 F g-1 at a current density of 1 A g-1.In a two-electrode system,the energy density can reach 7.02 Wh kg-1(0.1 A g-1).When the power density is 25.9 k W kg-1,the energy density can still be maintained at 5.04 Wh kg-1.3.Preparation of Fe-N-doped carbon nanorod and their electrocatalysts for oxygen reduction reaction.On the basis of the successful preparation of carbon fiber,the short rod polymer containing metal ion iron was further prepared by introducing Fe into the experiment in situ.The polymer was calcined at high temperature in ammonia atmosphere to obtain iron-nitrogen doped short rod carbon material.The catalytic properties of the material for oxygen reduction reaction at different pyrolysis temperatures were also investigated.Electrochemical measurements show that the oxygen reduction performance of Fe-N doped short rod carbon materials is even higher than that of commercial Pt/C materials under alkaline conditions.The onset potential is up to 1.0 V and the have-wave potential is 0.88 V.At the same time,the amount of the iron source is reduced,and the catalytic oxygen reducing property can still be maintained.The short rod structure provides shorter transport channels,and the doping of iron and nitrogen provides more active sites for catalytic oxygen reduction,which is beneficial to the catalytic performance of oxygen reduction reaction. |
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