Research And Development Of Supported Nickel-boron And Nickel-phosphorus Catalysts For Hydrazine Electrooxidation

A fuel cell is a chemical device that directly converts the chemical energy of a fuel into electrical energy.Direct hydrazine fuel cells?DHFCs?are expected to be used in mobile/portable power applications due to their high theoretical output voltage?1.56 V?,high energy density(5.40 kWh·kg^-1),and non-polluting environmental products.The development of low cost,high activity and good stability anode catalysts is the key to advancing the commercialization of DHFC.In this paper,DHFC anode catalysts were used as the research content.Different chemical synthesis methods were used to prepare low cost and high efficiency Ni-B and Ni-P supported catalysts.X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,and X-ray photoelectron spectroscopy?XPS?were used to characterize the morphology and structure of the catalyst.At the same time,Electrochemical methods,such as cyclic voltammetry,linear scanning and chronoamperometry,measure the catalytic activity and stability of the catalyst to establish the relationship between catalyst structure and performance.The research results obtained in this thesis lay the experimental and theoretical basis for the commercial application of DHFC.The main research contents of this paper are as follows:1.An electroless plating method was used to produce dense packed beadlets with an average size of 380 nm on the surface of foamed nickel to prepare supported Ni-B catalysts.Through XRD and selected area electron diffraction analysis,the catalyst is composed of amorphous and nanocrystalline.The catalyst exhibits good stability for the electrocatalytic oxidation of N₂H₄.At 30 ^oC electrocatalytic 0.10 M N₂H₄,its onset potential is-0.09 V,and at a potential of 0.30 V?relative to a reversible hydrogen electrode?,the current density reaches340 mA·cm^-2.Compared to the majority of DHFC anode catalysts that have been reported,this catalytic activity is at the leading level.In addition,the study found that appropriate increase in reaction temperature,hydrazine hydrate and sodium hydroxide concentration is conducive to the electro-catalytic oxidation of hydrazine.According to the comparison with the activity of Ni/nickel foam and XPS analysis of the valence state of the catalyst surface,the improved electrocatalytic performance may be due to the fact that doping B element regulates the Ni electronic structure and further enhances its intrinsic activity.2.Ni?OH?₂ precursor with nano-sheet structure was prepared firstly by using nickel foam as carrier,and a supported Ni-P catalyst was prepared by rephosphorizing.Through XRD and selected area electron diffraction analysis,Ni-P catalyst is composed of Ni₁₂P₅ and Ni₂P two phases.Under alkaline conditions,the performance of its electrocatalytic oxidation of N₂H₄was studied.The catalyst showed excellent activity and durability for N₂H₄ electrochemical oxidation.At the same potential,the Ni-P catalyst activity exceeds the Ni-B catalyst,but its onset potential is more positive.Combined with theory and experiment,the catalytic mechanism was discussed.The increase in electrocatalytic performance may also be due to the doping of P elements that regulates the Ni electronic structure,which in turn increases its intrinsic activity.