Preparation And Electrochemical Study Of Carbon-based Transition Metal Compound Composite Materials

With the increasing severity of energy crisis and environmental pollution,it is of great importance to exploit clean,cheap and efficient energy storage and conversion devices.Owing to its excellent conductivity,low cost,good structural stability and environmental friendliness,carbon-based materials have been widely studied and applied in fuel cells,metal-air batteries,lithium-ion batteries and supercapacitors.Oxygen evolution reaction,not only as an important anode reaction of electrolytic water reaction,but also plays a key role in metal air battery and renewable fuel cell,and is widely studied.The reaction involves four electron transfer process and slow kinetic rate,which makes it have worse reactivity and restricts its further development.At present,the commercialization of oxygen evolution catalysts relies on precious metals and their corresponding oxide materials?Ir,Ru,IrO2 and RuO2?,yet its low reserves,high cost and poor stability limit their actual large-scale usage.Therefore,it is vital to develop a new type of cheap and efficient carbon-based non-precious metal oxygen evolution catalyst.As a kind of energy storage,lithium-ion battery has become the most promising storage device because of its characteristics of high density,low working voltage,safe,reliable and friendly environment.However,the current commercial lithium-ion battery anode material is graphite carbon material,but its poor rate performance and lower theoretical capacity?372 mAh g-1?,which is difficult to meet the needs of high energy and power equipment development,so the development of new high capacity anode materials is of great significance.In this paper,a variety of transition metal composites were prepared by using electrospinning technique and inert salt template method,which were used as oxygen evolution reaction electrocatalysts and lithium-ion battery electrode materials,respectively,and showed high efficiency catalytic activity and higher specific capacity and cycling stability.At the same time,the synthesis method is simple and effective,it can be expanded to other carbon based transition metal materials,and its application in energy storage and conversion can studied.The main research contents are as follows:?1?A strategy was designed to effectively integrating transition metal oxides with carbon nanofibers.By employ electrospinning technology,we concurrently synthesize CoFe₂O₄ nanoparticles uniformly embedded in one-dimensional nitrogen-doped carbon nanofibers?denoted as CoFe₂O₄@N-CNFs?.The CoFe₂O₄@N-CNFs nanocomposites prepared by the synthesis of CoFe₂O₄ nanoparticles and nitrogen-doped carbon nanofibers have excellent oxygen evolution properties,which have smaller overpotential,larger current densities,smaller tafel slopes,and the stability of long-term operation in alkaline medium,which is superior to its corresponding single group material?pure CoFe₂O₄ and nitrogen doped carbon nanofibers?and commercial RuO2 catalysts.It is worth mentioning that the overpotential of CoFe₂O₄@N-CNFs at the current density of 30.0 mA cm-2 negatively shift 186 mV as compared with the commercial RuO2 catalyst,and the current density of CoFe₂O₄@N-CNFs at 1.8V is almost 3.4 times of that on RuO2 benchmark.The present work would open a new avenue for the exploration of cost-effective and efficient OER electrocatalysts to substitute noble metals for various renewable energy conversion/storage applications.?2?A two-dimensional carbon sheet synthesized by inert salt?KCl?template was developed to prepare composite materials with MoS0.5Se1.5 particles loaded with porous carbon nanosheets.The use of biomass fructose?C6H12O6?as a carbon source,ammonium molybdate??NH4?6Mo7O24 · 4H2O?,sodium selenite?Na2SeO3?,and thiosulfate?C2H5NS?,respectively as a source of Mo,Se and S.KCl as a template and dispersant,The as-prepared MoS0.5Sei.s uniformly dispersed in the ultrathin two-dimensional carbon nano-sheets material?denoted as MoSo.sSei.s/C?was obtained by the method of mechanical lapping and high-temperature calcination.As anode material for lithium-ion battery,compared with MoSe2/C material without S,MoSo.sSei.s/C shows better cyclic performance and rate performance,especially in the current density of 100 mA g-1,the capacity of 494.8 mA h g-1 is maintained after 200 cycles.This is much higher than the MoSe2/C material?173.5 mA h g-1?.The excellent Lithium storage performance of MoSo.sSei.s/C can be attributed to the combination of MoS0.5Se1.5 and porous carbon sheets synergy,and the porous carbon sheets can be used as an effective conductive matrix,as well as in charge and discharge process for lithium ion and electron transfer,active material MoS0.5Se1.5 volume expansion provides buffer space.?3?A two-dimensional carbon sheet prepared by using inert salt?NaCl?template was developed to prepare the Co2P particles loaded with porous nitrogen doped carbon nanosheets.Glycine?C2H5NO2?is used as a carbon-nitrogen source,ethylenediamine tetramethylene phosphoric acid?EDTMP?is a phosphorus source.By using NaCl as a hard template and dispersant,the Co2P particle modified porous nitrogen-doped carbon sheets?Co2P-N-C?is prepared and compared with other samples in alkaline media?Co-N-C,Co2P,N-C,C?showed excellent electrocatalytic activity,low overpotential and good stability for oxygen evolution reaction.The structural advantages of two-dimensional carbon nanoparticles and the doping of nitrogen atoms have effectively changed the electronic state of carbon materials,which are beneficial to the performance and stability of Co2P-N-C in oxygen evolution reaction.The preparation of this material has opened up a new way for the production of non-precious metal phosphate by macro quantity,and has a wide application prospect in the field of energy storage and conversion.