Preparation Of Nickel-based Catalyst And Its Application In Electrochemical Oxidation Of Urea

With the rapid development of modern society,global energy consumption is increasing day by day,and the energy crisis is becoming more severe.Therefore,it is urgent to develop green energy.Hydrogen energy has become the most potential clean energy due to its advantages such as high combustion value,green and renewable.Hydrogen production technology by electrolysis of water is considered to be one of the most promising hydrogen production methods.However,the development of electrolytic water hydrogen production technology is limited by the high reaction energy barrier of anodic oxygen evolution reaction（OER）.Urea oxidation reaction（UOR）can effectively reduce energy consumption due to its extremely low theoretical oxidation potential.It can also degrade urea-rich sewage and reduce environmental pollution.It has the potential to replace OER to improve the efficiency of hydrogen production by electrolysis.Nickel has better UOR activity than noble metals and is considered to be the best non-noble metal for urea electrolysis.Therefore,it is of great significance to explore cheap and efficient UOR nickel-based catalysts.In this study,different strategies were used to modify the nickel-based catalyst to improve the catalytic activity of UOR.The specific work is as follows:（1）A series of Ni-doped VOOH nanomaterials were successfully synthesized by one-pot method and their UOR performance was tested.The best UOR catalytic activity was obtained when V/Ni was 1/0.04 and the potential reached 1.356V at 10m A/cm².Lattice substitution doping subtly regulates the electronic structure and coordination environment of V/Ni cations,resulting in a synergistic interaction between V and Ni atoms,thus improving the catalytic activity of UOR.The asymmetric monolithic urea solution electrolyzer constructed with VOOH-Ni_0.04as the anode and Ni Co P with a HER overpotential of only 63 m V as the cathode can reach a current density of 10 m A/cm²with a driving voltage of only 1.494 V.Its good long-term stability of catalytic activity and low cost make VOOH-Ni_0.04a good choice for non-noble metal UOR catalyst in alkaline media.（2）Ni Cu-O（OH）/NF was synthesized on the surface of nickel foam（NF）by step-by-step hydrothermal method.Then,the precursor was vulcanized with thioacetamide as sulfur source to obtain S-Ni Cu-O（OH）/NF composite.XRD,HRTEM,XPS and other characterization methods proved that the composite was Ni₉S₈and Cu S coexisted with Cu₂O.The electrocatalytic activity of the catalyst was improved by interface construction and metal doping strategy.In the UOR and HER catalytic process,only 1.357 V and-0.146 V potentials are required to drive a current density of 10 m A/cm²,and the UOR and HER catalytic activity can be maintained after continuous electrolysis for up to 20 hours.On this basis,a symmetrical two-electrode urea solution electrolytic cell was constructed,which could reach 10m A/cm²at a low cell voltage of 1.47 V,which was 190 m V lower than that in water cracking at the same current density.Ni₉S₈/Cu S/Cu₂O/NF has good electrocatalytic activity,which is mainly due to the increased conductivity exposed to more active sites and the synergistic effect between Ni and Cu.Ni₉S₈/Cu S/Cu₂O/NF has certain practicability due to its dual function and good stability.（3）The bimetallic Ni Co MOF/NF with terephthalic acid as ligand was synthesized on NF by solvothermal method to prepare high efficiency UOR and HER electrocatalysts as co-precursors.After CV electrochemical activation,Ni Co MOF/NF can be converted into the corresponding Co（OH）₂and Ni（OH）₂.The potential of Ni Co MOF/NF is only 1.280 V at the current density of 10 m A/cm²,showing excellent UOR performance.In addition,the HER catalyst is prepared by phosphating Ni Co MOF/NF by solid-phase pyrolysis using sodium hypophosphite as the phosphorus source.Its main component is Ni Co P,and the overpotential of HER is only 63 m V.Electroactivation and phosphating make the surface of the catalyst amorphous,and more active sites are exposed,thus improving the catalytic activities of UOR and HER.Due to the excellent UOR and HER catalytic activities of Ni Co MOF/NF-EA and Ni Cop/NF,urea solution electrolytic cells were constructed by using them as anode and cathode,respectively.The cell only needs a low battery voltage of 1.447 V at a current density of 10 m A/cm²,and has good stability.This study shows that MOFs are good precursors for the preparation of high-efficiency electrocatalysts,and the powerful combination of different catalysts is an effective way to construct high-efficiency monolithic urea solution electrolyzers in addition to preparing bifunctional catalysts.