Synthesis And Electrocatalytic Properties Of Coal-based Carbon Fiber Supported Pd Composites For Formic Acid Oxidation

Due to the accelerated consumption of non-renewable resources and the worsening environment around the world,people turn their attentions to search for new energy sources.Direct formic acid fuel cell?DFAFC?has the advantages of friendly to environment,low permeability and low toxicity,so it has become one of the methods to solve energy and environment problems.However,the commercialization of DFAFC still needs to overcome the high price of anode catalyst Pd,low oxidation performance of formic acid,poor stability and poor resistance to CO poisoning.Therefore,solving the above problems is the key to the development of direct formic acid fuel cell.In this paper,coal based carbon fiber were prepared by electrospinning technology,and coal based carbon fibers were optimized by adjusting electrospinning parameters,based on the characteristic coal resources in Xinjiang as carbon source,and the catalyst supporter has an important influence on the performance of the catalysts.At the same time,suitable nitrogen and phosphorus sources were selected to prepare nitrogen and phosphorus dual doped coal based carbon fibers.This carbon material was used as catalyst supporter for Pd synthesis.On this basis,polyoxometalates with different alkyl chain length imidazoles were introduced.It is expected that the dispersion and particle size of Pd on nitrogen and phosphorus dual doped coal based carbon fibers can be further improved.Through the unique redox property of polyoxometalate,the anti CO poisoning activity of the composite catalyst was improved,thus the catalytic activity and stability of the composite were improved effectively.The main contents of this paper are as follows:?1?Oxidized coal was prepared by mixed acid treatment.Coal based carbon fibers was prepared by electrospinning,and the morphology of coal based carbon fibers was adjusted by controlling its spinning parameters.Different nitrogen and phosphorus sources were selected to prepare nitrogen and phosphorus dual doped coal based carbon fibers.Finally,nitrogen and phosphorus dual doped coal based carbon fibers with diameter of 225±31 nm,and specific surface area of 503.54 m² g^-1 was selected as the catalyst supporter for formic acid oxidation.?2?The composite catalyst was prepared by Pd supported on modified coal-based carbon fiber.The results of high resolution transmission electron microscopy?HRTEM?showed that the dispersion of Pd particles on the coal based carbon fibers doped with nitrogen and phosphorus was improved,and the particle size decreased to5.3 nm.The XPS results showed that the electron transport pathways of the catalysts were changed after nitrogen and phosphorus dual doped.The electrochemical test results show that the oxidation mass activity of formic acid of Pd composite supported by nitrogen and phosphorus dual doped coal based carbon fibers is up to 536.6 mA mg^-1 _Pd,whose stability and anti CO poisoning property are improved.?3?Four kinds of alkyl chain imidazole polyoxometalates(C₂,C₄,C₁₂ and C₁₆)were selected to synthesize composite catalyst materials with different alkyl chain length imidazole polyoxometalates.HRTEM showed that the particle size of Pd decreased with the increase of alkyl chain length of imidazole ionic liquid polyoxometalates.The composite catalyst prepared by C₁₆ imidazole ionic liquid polyoxometalate with the longest alkyl chain length has the smallest particle size of4.7 nm.The electrochemical performance of formic acid oxidation showed that the improved resistance to CO poisoning and electrochemical properties of the composites with the increase of the alkyl chain length of polyoxometalates in ionic liquids.The composite of imidazole ionic liquid polyoxometalates with the longest alkyl chain has the best electrochemical performance,and the oxidation mass activity of formic acid is 754.1 mA mg^-1 _Pd.The research contents of this paper will provide some reference for the high added value utilization of coal resources and the research,development and commercial application of catalyst materials for fuel cells.