Preparation And Electrocatalytic Performance Of The Mesoporous Transition Metal Carbide Carbon-based Material

It is urgent to develop a cleaner energy source for maintaining the sustainable development of human society.The fuel cell is a technology that can convert chemical energy directly into electric energy with high energy density and clean energy transition processes.However,the bottleneck problem in the large-scale commercialization of fuel cell is that the performance of the non-noble metal catalyst for ORR on the cathode of fuel cell cannot meet the practical demands.The development of the non-noble metal catalysts with high performance and low cost is an effective way to promote the large-scale commercialization of fuel cells.Transition metal carbide materials possess several merits,such as abundant resources,low price,high conductivity,high hardness,high melting point,excellent thermal stability,high stability in acid and alkaline medium,and the "platinum-like" electronic structure and catalytic ability.So this kind of catalyst possesses great application potential and research value in the field of electrode materials.Nevertheless,there are few studies on the synthesis and electrocatalytic properties of transition metal carbides.In this thesis,we report that a series of novel titanium nitrogen-oxide electrode materials supported by transition metal carbides and ordered mesoporous carbon-based materials containing the transition metal carbides nanoparticles were prepared by a simple coating pyrolysis method or perfusion-etching method using the functionalized ionic liquid,titanium nitrogen-oxide electrode and SBA-15 molecular sieve as the basic materials.The prepared materials were characterized in detail.Their electrochemical catalysis were systematically investigated.The results show that these materials have the best electrocatalytic activities,significantly higher than those of similar materials reported in the literature.The research contents are as follows:1.Two new transition metal functionalized ionic liquids[Hmim]₂[Cr₂O₇]?1-heptyl-3-methyl imidazole chromate?and[Bmim]₃[VO₄]?1-butyl-3-methylimidazolium vanadate?were designed and synthesized by ion-exchange preparation method.Other two transition metal functionalized ionic liquids[Bmim]₂[MoO₄]?1-butyl-3-methylimidazolium molybdate?and[Bmim]₂[WO₄]?1-butyl-3-methylimidazolium tungstate?were synthesized according to literatures.The molecular structure and the pyrolysis behavior of the four ionic liquids were investigated using infrared spectroscopy?IR?,nuclear magnetic resonance spectroscopy?NMR?and thermogravimetric analysis?TG/DTA?methods.2.The titanium nitrogen-oxide electrode was synthesized by using the method of heating metal titanium in oxygen,and then heating the obtained titanium oxide in nitrogen with tripolycyanamide as nitrogen source.Molybdenum carbide,tungsten carbide,chromium carbide and vanadium carbide particles were successfully supported on the titanium nitrogen-oxide electrodes by the ionic liquid coating-pyrolysis method,prepared a series of composite electrode materials such as Ti-TiN_xO₂-X-MoC,Ti-TiN_xO₂-x-WC,Ti-TiN_xO₂-x-Cr₇C₃,Ti-TiN_xO₂-x-V8C7,and so on.These electrodes were investigated by X ray diffraction?XRD?,scanning electron microscopy?SEM?,energy spectrum?EDS?,X ray photoelectron spectroscopy?XPS?methods,and their catalytic activity of HER?the hydrogen evolution reaction?,ORR?oxygen reduction reaction?,and partial oxidation reaction of ethanol was studied.The onset potential over these catalysts increases 20%-50%for HER and 10%-20%for ORR compared with the transition metal carbides reported in the literature,the selectivity of acetaldehyde as the product over these catalysts increase 18%-23%compared with the platinum electrode.It was proved that the titanium-titanium-nitrogen-oxide-based electrodes supported by transition metal carbide prepared by the ionic liquid coating-pyrolysis method were the multifunctional electrocatalytic materials.3.The carbon based mesoporous materials containing molybdenum carbide nanocrystals could be obtained by grinding impregnation of ionic liquids and SBA-15 molecular sieve as hard template at room temperature,calcinating samples in nitrogen and etching procedure in acidic solution.The molybdenum carbide mesoporous materials were characterized by XRD,SEM,TEM,and XPS methods,and it was showed that the material possesses 132 m² g^-1.The investigation of HER and ORR showed that it was a good double functional electric catalyst.The onset potential of HER over it is 20-112 mV higher than those over the molybdenum carbide nano materials reported in the literature,and the onset potential for oxygen reduction is 90-220 mV higher than those over the reported molybdenum carbide materials.In both of acid and alkali environment,which can maintain stable electrochemical performance.4.A new method for preparing the ordered mesoporous carbon-based material containing the tungsten carbide nanoparticles was developed.By grinding dipping-pyrolysis-acid etching procedure using tungstate ionic liquid as theprecursor of tungsten and carbon SBA-15 as hard template.By this method,the prepared mesoporous materials was composed of tungsten carbide nano crystalline and by partial graphitizing carbon with the nanocrystal size of about 5 nm.and the specific surface area of 144 m² g^-1.The carbon-based mesoporous tungsten carbide material can be used as a kind of non-noble metal catalyst in HER and ORR.The results showed that the onset potential over the prepared tungsten carbide nanomaterials is 20-230 mV for HER and 10-300 mV for ORR higher than that over those reported in the literature.The tungsten carbide mesoporous materials showed stable electrochemical properties in both acid and alkali environments.5.The synthesis method of the carbon-based chromium carbide mesoporous materials was reported for the first time using functionalized ionic liquids.Based on this method,the carbon based mesoporous chromium carbide was prepared,contains the chromium carbide nanocrystals of about 2-4 nm and possesses the specific surface area of 149 m² g^-1.The mesoporous chromium carbide material showed outstanding performance in HER and ORR.The onset potential over the prepared materials is 70-200 mV for HER and 80 mV for ORR higher than those over chromium carbide materials in literatures.This material showed stable electrochemical performance in acid and alkali environment.6.The vanadate functionalized ionic liquid precursor were used in the synthesis of carbon based vanadium carbide mesoporous materials with vanadium carbide nanocrystal size of about 5 nm,and the surface area of the material of 133 m² g^-1.As a non-noble metal catalytic materials for HER and ORR,the prepared materials were investigated.The results indicate that the onset potential over the prepared materials is 360 mV for HER and 130 mV for ORR higher than those over vanadium carbide materials in literatures and its stable performance could be maintained in both acid and alkali environment.To sum up,the method for synthesizing carbon-based transition metal carbide mesoporous materials based on functionalized ionic liquids gives a new way to synthesize nano transition metal carbide materials.This method is suitable for preparing a variety of transition metal carbides nanoparticles,and has advantages such as simple operation,low energy consumption.The prepared transition metal carbide materials exhibit the excellent electrocatalytic performance for ORR and HER.