Preparation Of Nickel-based Hydroxide Nanomaterials And Their Electrocatalytic Properties For Urea Oxidation

Urea is a promising hydrogen carrier,so it is important to study the use of urea as hydrogen carrier for purifying environment and developing new clean energy.Direct urea fuel cells are of great importance in energy-related applications,but their oxidation kinetics are slow,so the use of efficient nanostructured catalysts to increase kinetic rates is considered an effective strategy.Nickel-based hydroxide is considered to be an inexpensive material with good stability and catalytic activity,but its catalytic activity needs further improvement.Therefore,the development of nickel-based catalysts is considered to be a significant and valuable research direction.The aim of this work is to prepare nickel-based hydroxide catalysts by hydrothermal method,to investigate the effects of introducing foreign metals and changing the ratio of foreign metals on the structure,morphology and catalytic performance of nickel-based catalysts for the synthesis of nickel-based hydroxide and nickel-copper-cobalt ternary nickel-based hydroxide catalysts,specific elements include the following:（1）Preparation of nickel（II）hydroxide with porous structure and investigation of the growth mechanism of nickel（II）hydroxide.（2）The preparation of Ni-Co and Ni-Cu hydroxide with different ratios was investigated,and their morphologies and structures were characterized.（3）Investigate the preparation of Ni-Cu-Co ternary hydroxide with different ratios,and to investigate the preparation of Ni-Cu-Co ternary hydroxide with double hydroxides and another metal.（4）Electrochemical methods were used to investigate the UOR performance of the catalysts,and to analyze and explain the differences of the UOR performance of the catalysts.The results and conclusions are as follows:（1）The porous nickel（II）hydroxide nanowire was prepared from HMT and its growth mechanism was investigated.The cyclic voltammetry curve of urea electrocatalytic oxidation showed that the peak current density of the catalyst was1.45 A g^-1 and the initial potential was 400 m V.（2）The addition of foreign metal ions can significantly affect the nickel（II）hydroxide morphology and further affect the catalytic performance of the prepared catalysts.The experimental results show that the catalyst has the best comprehensive performance when HMT is used as base source and the ratio of Ni（NO₃）₂ to Co（NO₃）₂ is 4:1 and Ni（NO₃）₂ to Cu（NO₃）₂ is 7:1,at the same time,the micro-morphology of nano-flower with porous structure is preserved.The cyclic voltammetry curve of urea electrocatalytic oxidation showed that the peak current density was 5.35 A g^-1 and the initial potential was 331.5 m V when the ratio Ni（NO₃）₂:Co（NO₃）₂ was 4:1,when the ratio of Ni（NO₃）₂ to Cu（NO₃）₂is 7:1,the peak current density of the catalyst is 3.72 A g^-1,and the starting potential is 340.7 m V.（3）Multi-component nickel-based hydroxide can further enhance the UOR performance of nickel-based catalysts.The results showed that the Ni-Cu-Co ternary Ni-based hydroxide catalysts prepared by doping 0.7 mmol Co（NO₃）₂ with Ni（NO₃）₂ and Cu（NO₃）₂ at a ratio of 7:1 had the best comprehensive performance,at the same time,the micro-morphology of nano-flower with porous structure is preserved.The peak current density is 5.46 A g^-1,and the starting potential is only321.8 m V.The prepared nickel-based hydroxide catalysts have important basic research significance for the electro-oxidation of urea and the development of direct urea fuel cells.