Preparation And Application Of Schiff Alkali Metal Complex-derived Carbon-based Materials

With the rapid development of industry around the world,oil,known as the blood of industry,has been widely used,which has greatly promoted the development of economy and provided great convenience for people's life and travel.However,with the use of oil and other traditional fuels,energy crisis,environmental deterioration and other problems have gradually emerged,and been constantly concerned by people.Restricted by the Carnot cycle,the energy conversion rate of traditional fuels is low,but the emission pollution caused by them is serious,which is not conducive to the long-term sustainable development of society.Therefore,the development of new energy and its energy devices has become the focus of the world.In this context,the development of direct ethanol fuel cell(DEFCs)has attracted much attention,which is attributed to its ability to efficiently convert the chemical energy of ethanol into electrical energy for energy supply,and ethanol as a fuel has certain advantages,such as renewable,low toxicity,environmental friendliness,etc.As the key material of DEFCs,anodic catalyst is the key to the energy output and stability of DEFCs.Precious metal Pd is a common DEFCs catalyst.However,its poisoning prone characteristics make it difficult to be applied in the field of DEFCs.Research on high-performance catalysts has been one of the hot spots and major challenges in the field of DEFCs.In this paper,we prepared carbon based materials with different transition metal elements and structures based on Schiff base transition metal complexes.We have improved the catalytic activity and stability of ethanol oxidation reaction(EOR)catalysts from the perspective of preparation of support materials.Specific research contents are as follows:(1)O-vanillin thiourea schiff base and its nickel complex precursor have been synthesized using cheap chemical raw materials o-vanillin and thiourea.They were pre-carbonized by infrared pre-carbonization technology.The pre-carbonized materials were carbonized at different temperatures to prepare heteroatom doped carbon(HDC)materials containing metal sulfide.HDC-750 prepared at 750?has abundant heteroatoms and unique three-dimensional pore structure.This structure not only improves the permeability of the electrolyte,but also increases the anchor points of a large number of Pd nanoparticles,which is beneficial to increase the electrochemical active area of the catalyst.When the HDC-750 is used as the carrier of Pd nanoparticles,the direct or indirect electronic interaction between Pd nanoparticles and the carrier and Ni₃S₂in the carrier can promote the removal of reaction intermediates,and significantly improve the EOR activity and durability of Pd/HDC-750.(2)Vanillin L-arginine cobalt complex has been prepared from vanillin and renewable arginine,and high graphitized carbon based material(HGC)was obtained by direct carbonization.HGC has a unique nano cavity and mesoporous structure,and also contains a small amount of Co nanoparticles.Unlike commercial carbon powder,HGC contains a large number of graphene like structures to increase its own conductivity and reduce the load transfer resistance.The Pd/HGC catalyst was prepared using HGC as support material.The results show that the EOR activity of Pd/HGC catalyst is higher than that of Pd/C.The mass activity of Pd/HGC catalyst is 1686 mA mg _Pd^-1,which is 4.0 times of that of Pd/C,and its stability is better than that of Pd/C.The main reason is that the three-dimensional structure of HGC with a large number of cavities and mesopores is conducive to the loading of Pd,the permeation of electrolyte and the desorption of products(including intermediate products).In addition,the HGC with graphene structure can effectively reduce the resistance of the catalyst and improve the charge transfer efficiency of EOR.(3)The o-vanillin L-aspartic acid copper complex was prepared from o-vanillin and renewable aspartic acid,and the complex derived carbon-based material Cu-C was obtained by low temperature pre-carbonization.The Pd/Cu-C catalyst prepared with Cu-C as the support material of Pd can be used as a bifunctional catalyst for electrocatalytic oxidation of formic acid or ethanol in acidic or alkaline environment.The Pd/Cu-C catalyst can obtain higher alkaline EOR activity and acidic formic acid oxidation reaction(FAOR)activity.The mass activity is 3.7 and 2.1 times of that of Pd/C,respectively,and its stability is also higher than that of Pd/C.This is due to the high content of Pd⁰species in the Pd/Cu-C,which increases the number of active sites for catalysis,thus increasing the adsorption amount of reactants on the surface of the catalyst and improving the reaction rate.