Preparation Of Nickel-based Hydroxide Nanomaterials And Their Catalytic Performance For Urea Electro-oxidation

Urea,a rich chemical hydrogen-containing material,is a new energy source with broad application prospects.Direct urea fuel cells（DUFCs）are the most effective technology to play the new energy function of urea.Although its theoretical mass energy density is very high,due to the slow kinetics of the urea electro-oxidation reaction（UOR）,the performance of DUFC still depends heavily on the research and development of anode catalysts.Many studies have shown that nickel-based materials,as a non-precious metal catalyst,exhibit good catalytic activity for the electrooxidation of urea in alkaline media,but its activity and stability need to be further improved.The work of this thesis focuses on the anode catalyst problem of direct urea fuel cell,aims at the development of non-precious metal catalysts,selects nickel-based nano-hydroxide as the research object,carries out the corresponding preparation and catalytic performance research,the purpose is to understand the alkali source and metal elements The influence of factors such as ratio on the structure and morphology of nano-hydroxide,and an in-depth understanding of the relationship between the preparation-structure-performance of nickel-based nano-hydroxide.The main research content includes the following three parts:（1）Use hydrothermal method to study the preparation of nano-nickel hydroxide with different structures and morphologies,investigate the influence of different alkali sources on the structure and morphology,and explore the formation mechanism of nano-hydroxides;（2）Study the preparation of nickel-cobalt and nickel-manganese double hydroxides,and investigate the effects of different doping ratios on the structure and morphology of multiple products;（3）Cyclic voltammetry,chronoamperometry,Tafel curve,and electrochemical impedance spectroscopy are used to investigate the catalytic performance of the prepared catalyst for the electrochemical oxidation of urea.Through the analysis of material characterization and catalytic performance data,explain the effect of the prepared catalyst.The difference in electrocatalytic oxidation performance of urea.The experimental results and conclusions obtained are:（1）The choice of the alkali source has a significant impact on the microstructure and morphology of the prepared samples:the samples prepared with ammonia as the alkali source show the morphology of nano-sheet stacking;the samples prepared with the HMT as the alkali source show Honeycomb porous curd structure;samples prepared with urea as an alkali source show a sea urchin-like structure.The catalytic activity of the three samples is strong or weak,which can be explained to a certain extent from their structure and morphology.The sea urchin-like 3Ni（OH）₂·2H₂O prepared with urea as an alkali source has the largest specific surface area and has more reaction sites to adsorb urea and catalyze its oxidation.The maximum current density for electrocatalytic oxidation of urea can reach 5.59 m A cm^-2,the starting potential is about 326.6 m V.（2）The presence of nickel helps to form a sea urchin-like structure and morphology similar to Ni（OH）₂,and its porosity and high specific surface area are beneficial to catalyze the electrochemical oxidation of urea.Among the four samples prepared,the nickel-cobalt composite catalyst prepared with urea as the alkali source and the molar ratio of nickel and cobalt at 2:1 has the highest catalytic activity for UOR,the largest current density and the smallest charge transfer resistance.,The lowest oxidation onset potential and the smallest Tafel slope.The maximum current density of the composite catalyst for electrocatalytic oxidation of urea can reach 0.36m A cm^-2,and the initial potential is about 353.4 m V.（3）The presence of nickel and manganese has a significant impact on the microstructure and morphology of the product.Among them,nickel ions are easy to form Ni（OH）₂,resulting in the formation of porous flower-like or network-like microspheres,while manganese The ions generated under hydrothermal reaction conditions are characterized by a cubic structure of Mn CO₃,resulting in the product showing solid microspheres or irregular block particles.Among the four samples prepared,the nickel-manganese composite catalyst prepared with urea as the alkali source and the molar ratio of nickel and manganese at 2:1 has the highest catalytic activity for UOR,the largest current density and the smallest charge transfer resistance.The lowest oxidation onset potential and the smallest Tafel slope.The maximum current density of the composite catalyst for electrocatalytic oxidation of urea can reach 0.44 m A cm^-2,and the initial potential is about 331.4 m V.A comprehensive analysis of all experimental results shows that in all the samples prepared,sea urchin-likeα-3Ni（OH）₂·2H₂O porous nanomaterials prepared with urea as an alkali source and Ni（NO₃）₂ as a nickel source have a significant effect on the electrooxidation reaction of urea.The best catalytic performance.This strongly shows that for the electrooxidation reaction of urea,Ni（OH）₂ is the most important active component in nickel-based catalyst materials;the catalyst structure and morphology bring about different specific surface areas,accessibility and active sites.The number of dots is also an important factor affecting the catalytic activity.The work in this thesis is an active exploration of the development of anode catalysts for direct urea fuel cells.The results obtained have important guiding significance and application reference value for further catalyst preparation and performance research.