Preparation Of Self-supported Nickel-based Hydroxide Electrodes And Their Electrocatalytic Properties Towards Urea Oxidation

Urea oxidation reaction（UOR）has shown great application prospects in the field of the technologies of electrolysis hydrogen production and direct urea fuel cell,but the overall reaction efficiency is limited by its slow kinetic process.Various material design and synthesis strategies to optimize the performance of the catalyst were developed,such as morphology design,structural decomposition,defect engineering,electronic conversion,replacement technology,heterogeneous structure building et al.At present,nickel-based materials are the one of the most active UOR catalysts,but their catalytic activity needs to be further improved.In this thesis,self-supporting electrodes with high UOR catalytic activity were prepared based on nickel hydroxide,and the method of heterojunction design and structure control were used to improve the performance of catalysts.The specific research contents are as follows:（1）Ni（OH）₂ was grown on the surface of NiMoO₄ by a step-by-step construction method to form a heterogeneous phase interface,and the Ni（OH）₂/NiMoO₄ self-supporting electrode was prepared.SEM characterization shows that the morphology of NiMoO₄ was a porous structure formed by nanosheets interspersed with each other,which is conducive to mass transfer.Collapsed hemispherical Ni（OH）₂ was grown on the surface of the NiMoO₄ nanoarray.The rich heterogeneous phase interface provides a large number of active sites for the catalytic reaction.The introduction of high-valence molybdenum is conducive to promote the conversion of Ni（OH）₂to Ni OOH,and Ni³⁺is considered to be the active site,so Ni（OH）₂/NiMoO₄/NF materials exhibit excellent catalytic UOR performance.In 1 M KOH+0.33 M CO（NH₂）₂electrolyte,the potential of Ni（OH）₂/NiMoO₄/NF at 10 m A cm^-2 was only 0.40 V vs.Hg/Hg O.At 0.7 V vs.Hg/Hg O,the current density of catalyst was up to 207 m A cm^-2,and it had a good stability.（2）The NiCo LDH/NiCo（OH）₂self-supporting heterojunction electrode material was prepared by solution method at room temperature.TEM and XRD analysis showed that the NiCo LDH/NiCo（OH）₂ heterojunction material exists in the form of micrometers assembled from ultra-small nanosheets.The abundant heterojunction interface provided a great number of active sites,and at the same time,the material exhibited excellent electrochemical performance due to the synergistic effect of bimetallic properties.The electrochemical results showed that in1 M KOH+0.33 M CO（NH₂）₂ electrolyte,the potential of NiCo LDH/NiCo（OH）₂ electrode at the current density of 10 m A cm^-2was about 0.34 V vs.Hg/Hg O.At 0.7 V vs.Hg/Hg O,the current density of NiCo LDH/NiCo（OH）₂ was about 200 m A cm^-2,which was much higher than that of Ni（OH）₂ and Co（OH）₂.NiCo LDH/NiCo（OH）₂ heterogeneous material was a promising urea electrooxidation catalyst and provided a new idea for the design of high-performance nickel-based catalysts.（3）The EDTA^4-intercalated nickel-cobalt layered bimetallic hydroxide（NiCo LDH）self-supporting electrode material was prepared by the high-temperature hydrothermal method,and the conformal transformation was further realized in the KOH solution,and finally obtained CO₃^2-intercalated NiCo LDH（NiCo LDH-1/NF）.Material characterization showed that NiCo LDH achieves partial exfoliation during the conformal transformation process,which was beneficial to provide more edge active sites and improve the performance of UOR.The electrochemical results showed that NiCo LDH-1/NF has excellent catalytic UOR performance.In 1 M KOH+0.33 M CO（NH₂）₂ electrolyte,the potential of NiCo LDH-1/NF was 0.342 V vs Hg/Hg O at the current density of 10 m A cm^-2.At 0.7 V vs Hg/Hg O,the current density of NiCo LDH-1/NF was as high as 246 m A cm^-2,and it had an excellent stability.