Research On High-performance Catalysts For Hydrogen Production From Urea-assisted Water Electrolysi

In the context of sustainable development,electrolysis of water to produce hydrogen is currently a relatively environmentally friendly way of producing hydrogen energy.Hydrogen production by electrolysis of water includes cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）,but the slow kinetics of oxygen evolution reaction leads to high energy consumption and increases the cost of hydrogen production.In order to better solve this problem,reactions with lower theoretical potentials,such as urea oxidation reaction（UOR）,can be used to replace the OER at the anode end.Therefore,urea assisted electrolysis of water for hydrogen production is an effective and feasible method.The reported HER and UOR catalysts are usually limited by the high cost of precious metal materials,or the low catalytic activity and poor cycling performance of transition metal materials.Therefore,it is of great significance to design and prepare electrocatalysts for urea assisted electrolysis of water to produce hydrogen technology,which can simultaneously have lower costs,higher activity,and better stability.In response to the above challenges,this research project has successively designed and prepared NiRu/NiO and Ru-NiSe₂ for HER,and Ni-MnO₂ for UOR.The main contents are as follows:1.Acetate was added to the precursor of metal organic frameworks（MOFs）by hydrothermal method to transform the product of the hydrothermal reaction from MOFs to NiRu/Ni（OH）₂.NiRu/Ni（OH）₂ was then calcined to synthesize NiRu/NiO catalysts with heterogeneous structures.Experimental studies have found that the alkaline environment provided by acetate is conducive to the decomposition of N,N-dimethylformamide（DMF）into dimethylamine（C₂H₇N）and carbon monoxide（CO）,which can reduce metal salts to metal monomers.Acetate ions are also beneficial for the synthesis of hydroxides,and together,NiRu/Ni（OH）₂ is formed.NiRu/NiO prepared in alkaline electrolyte has an overvoltage of 18m V and Tafel slope of only 43.3 mV dec^-1 when the current density is 10 mA cm^-2,which proves that NiRu/NiO has excellent HER performance.At the same time,this work also provides a new strategy for the synthesis of metal/metal hydroxide（metal/metal oxide）.2.Ru-NiSe₂ material was synthesized on foam nickel substrate by hydrothermal method and ion exchange method.The introduction of Ru makes Ru-NiSe₂ have large electrochemical active surface area and suitable electronic structure.Experiments have shown that Ru-NiSe₂ exhibits excellent HER activity in 1 M KOH solution.At an overvoltage of 180.8 mV,its current density can reach 1000 mA cm^-2.Due to its inherent structural stability and strong catalyst support interface,the catalyst can work continuously for 90 hours at a current density of 1000m A cm^-2,and the overvoltage only increases by 13 mV.The excellent HER performance of Ru-NiSe₂ indicates its great potential for application in industrial electrolytic water.3.Nidoped MnO₂（Ni-MnO₂）nanosheet arrays were successfully prepared on foam nickel by hydrothermal method and ion exchange method.It is worth noting that a low potential of 1.388 V vs.reversible hydrogen electrode（RHE）is required on Ni-MnO₂ to achieve a high current density of 100 mA cm^-2.Research has shown that nickel doping and nanosheet array structure are the reasons for the high UOR activity of Ni-MnO₂.The introduction of Nihas changed the electronic structure of Mnatoms and generated more Mn³⁺species in Ni-MnO₂,which is conducive to achieving excellent UOR performance.