Preparation Of Nickel-based Electrode Materials By Hydrotalcite Precursor Method And Their Electrochemical Properties

In the face of depleting fossil energy sources and the resulting environmental pollution,more and more researchers are looking for sustainable,clean,and environmentally friendly ways to produce and store energy.Direct ethanol fuel cells（DEFCs）and supercapacitors are both promising energy conversion and storage methods.Recent studies have shown that nickel-containing hydrotalcites（LDHs）have good activity as both ethanol oxidation catalyst materials and supercapacitor materials,but still suffer from slow rates of conduction of electrons and ions,which limit their further practical applications.In this thesis,based on improving the electron and ion conduction rates of LDHs-based electrode materials,two nickel-based electrode materials（Ni O/Ni₃Fe/Ce_xO_y/Ni Fe O_xandβ-Ni（OH）₂）were prepared by two strategies,H₂reduction and KOH solution etching,respectively,using nickel-containing LDHs as precursors,and the composition,structure and morphology of the materials were meticulously characterized and analyzed,respectively The ethanol-catalyzed oxidation and supercapacitance properties of the materials were tested.The main research contents and results are as follows:（1）Ce/Ni Fe-LDHs precursors were synthesized by hydrothermal method,and Ni O/Ni₃Fe/Ce_xO_y/Ni Fe O_xcomposites were prepared by partial reduction of the precursors in flowing H₂for ethanol electrocatalytic oxidation reaction.The results showed that Ce⁴⁺in the precursor was converted to Ce³⁺by H₂reduction,and abundant oxygen vacancies were formed in the structure of Ni O/Ni₃Fe/Ce_xO_y/Ni Fe O_xcomposites,with the highest content of oxygen vacancies when the reduction temperature was 350℃.The electrocatalytic oxidation reaction of ethanol was carried out under alkaline conditions to evaluate the electrocatalytic performance of the catalyst samples.Compared with the precursors,the composites prepared by reduction at 350°C exhibited stronger catalytic activity（～6.1 times higher compared to the LDHs precursors）,smaller electron transfer resistance（25.98Ω）and lower onset potential（0.45 V）,and good cycling stability（only 5%loss rate after 3600 s）.The increased content of oxygen vacancies and the presence of Ni₃Fe nanoalloy substances effectively improved the electrocatalytic activity of the complex materials.（2）Ni Al-LDHs precursors were synthesized by the urea method,and thenβ-Ni（OH）₂was prepared by etching with different concentrations of KOH solution.The effect of the alkali solution concentration on the structure,morphology,specific surface area and porous structure of the resulting samples was investigated by selectively dissolving the amphiphilic Al³⁺ions in LDHs with KOH solution,and the in situ topography of Ni Al-LDHs precursors The mechanism ofβ-Ni（OH）₂formation by conversion of Ni Al-LDHs precursors was investigated.Compared with the LDHs precursors andβ-Ni（OH）₂prepared by co-precipitation reaction,the samples prepared by alkali etching in 10 M KOH solution have the largest specific capacitance(829 F g^-1at 1 A g^-1),high multiplicity capability(57.3%capacitance retention at a current density of 8 A g^-1)and good charge/discharge stability.Theβ-Ni（OH）₂sample prepared by alkali etching has a large specific surface area and abundant porous structure,which makes the contact between the active component of the material and the electrolyte solution more adequate and can effectively improve the capacitive performance of the sample.