Study On The Electro-chemical Oxidation Of Urea With Ni-base Nanometer Rod-like Catalyst

Direct urea fuel cell(DUFC)is a new type of fuel cell that uses urea to generate electricity and it has great potential in energy sustainable development.However,the performance of urea fuel cell is not enough to compare with other types of fuel cells,because the anodic oxidation reaction is a six-electron transfer process and the dynamics are slow.At present,the emphasis of the research is to develop high efficient catalyst for urea anodic oxidation.It has been found that the non-noble metal nickel catalyst has better catalytic performance for the oxidation of urea,but it has disadvantages such as high initial potential of urea oxidation,poor stability,low current density,etc.Therefore,different nickel-based catalyst materials have been prepared to improve the kinetics of urea oxidation.The purpose of this paper is to prepare nickel-based composite nano-catalysts by simple hydrothenrial and calcining methods,and to introduce relatively cheap iron,cobalt and molybdenum elements to improve the performance of urea oxidation.The synergistic effect between bimetals was used to inprove the catalytic performance of the nickel-based catalyst for urea oxidation,and carbon black was added to improve the electrical conductivity of the catalyst,including the following three parts:1.Electrooxidation of urea is catalyzed by rod-shaped nickel-iron oxide catalyst.Nickel-iron oxide was prepared by first synthesizing precursor by one-step hydrothermal method and then calcining in tube furnace.Its structure,moiphology and surface composition were studied by means of physical characterization such as powder X-ray diffractometer,transmission electron microscope and X-ray photodectron spectroscopy.The catalytic performance and kinetic analysis of urea oxidation were obtained by measuring cyclic voltammetry and electrochemical impedance spectroscopy.Comparing with NiO/Fe2O3/FeNi3-l and NiO/Fe2O3/FeNi3-3,the results showed that NiO/Fe2O3/FeNi3-2 had the best catalytic activity for urea oxidation.The maximum current density of urea oxidation can reach 36.6 mA cm'2,and the onset potential was about 265.3 mV vs.SCE.2.Electrooxidation of urea is catalyzed by rod-shaped nickel-cobalt oxide catalyst.The preparation of nickel-cobalt oxide firstly synthesizes precursor material by hydrothermal method and then prepares catalyst by calcining in tubular furnace.Its structure,morphology and surface composition were studied by means of physical characterization such as powder X-ray diffractometer,transmission electron microscope and X-ray photoelectron spectroscopy.The catalytic performance and kinetic analysis of urea oxidation were obtained by measuring cyclic voltammetry and electrochemical impedance spectroscopy.The catalytic capacity of urea was regulated by changing the ratio of different Ni-Co precursors(the molar ratio of Ni/Co is 1:1,1:2,1:3).The pure phase NiCO2O4 catalyst prepared with Ni/Co molar ratio of 1:2 had a maximum current density of 65.7 mA cm-2and the onset potential was about 0.22 V vs.SCE.3.Urea electro-oxidation catalyzed by nickel-molybdenum oxide nanorods.Ni-Mo oxide nanorods were prepared by the ratio of different Ni-Mo precursors,and their crystal structure,morphology and surface element composition were characterized by powder X-ray diffractometer,Raman spectrum,transmission electron microscope and X-ray photoelectron spectroscopy.The catalytic performance and kinetic analysis of urea oxidation were obtained by measuring cyclic voltammetry.The process that urea was catalyzed by Ni-Mo oxide was an electrochemical-chemical reaction mechanism,and also the redox of NiOOH/Ni(OH)2 occurred at high potential.The catalytic capacity of urea was regulated by changing the ratio of different Ni-Mo precursors,and the catalyst material of N1M0O4-C(Ni-Mo:2:1)had fast kinetics,small charge transfer resistance and low tafel slope,so it had the best catalytic performance for the oxidation of urea.The ideal electrocatalytic activity,stability and durability for urea oxidation indicate that it has broad application prospects in sustainable energy technology and water pollution reduction.