Study Of Microwave Method For Preparation Of Two-Dimensional Transition Metal-Based Compounds And Their Electrocatalytic Properties

Electrocatalytic water splitting is an important means to solve energy and environmental problems.The key to improving the performance of electrocatalytic water splitting is the preparation and modification of electrode materials.Traditional electrode materials are mostly zero-dimensional nanoparticles made by noble metals.But their wide application is limited by the low reserves and high cost,which affects the development of electrocatalytic water cracking.Transition metal catalyst is a potential substitute catalyst with low cost and abundant structure.At the same time,the two-dimensional structure design can avoid the aggregation,maintain a good active exposure area,and the two-dimensional structure have a stable charge transport path,which is conducive to the improvement of catalytic activity and stability.However,traditional preparation and modification methods of electrode materials are usually requiring long time of high temperature furnace,or harsh reaction conditions,which affects the cost of production and material activity.Therefore,it is necessary to explore new methods to simply and rapidly optimize the preparation and modification of electrocatalytic materials.Microwave has been wildly used in the preparation and modification of functional materials because of the properties of selective heating,high energy,simplicity and convenience.However,the two-dimensional structural design system of oxides and carbides based on microwave strategy still needs to be improved.Focusing on this program,we designed the two-dimensional structure of transition metal carbide and perovskite oxides by microwave method,and explored in detail the application of tungsten carbide,strontium doped lanthanum cobalt oxide and nickel doped lanthanum manganese oxide in electrocatalytic water splitting.The specific research contents are as follows:（1）The ultra-fast and simple synthesis of ultra-thin two-dimensional transition metal carbides with carbon-terminated is achieved by microwave pulse sugar blowing method.The method can rapidly obtain a series of two-dimensional transition metal carbides within 3 min,and can precisely adjust the thickness of the terminated carbon.The electrocatalytic activity and stability of the prepared two-dimensional transition metal carbides are significantly improved.The high HER activity and long endurance（100 h）in both acidic and alkaline electrolytes is shown by the sample of 2D W₂C with carbon layer thickness of 1 nm.In addition,the two-dimensional WC,Mo₂C and MoC is universal prepared by the microwave pulse sugar blowing method.（2）Two-dimensional porous La_0.2Sr_0.8CoO₃ perovskite is rapidly prepared by microwave shock method.The rapid entropy increase accompanying the microwave process can effectively expose the abundant active sites in the La_0.2Sr_0.8CoO₃ structure.In addition,the high-energy microwave shock process can precisely introduce Sr²⁺into the LaCoO₃ lattice,and the replacing of La by Sr can significantly improve the intrinsic catalytic activity by increasing the oxidation state of Co to increase the number of oxygen vacancies.The prepared La_0.2Sr_0.8CoO₃ catalyst has perfect OER performance with an overpotential of 360 m V at 10 m A·cm^-2 and a Tafel slope of 76.6 m V·dec^-1.After a long-term test of 30,000 s,the current density remains at 97%of the initial current density in alkaline electrolyte.（3）A series of two-dimensional porous nickel doped lanthanum manganese perovskite oxides are prepared by microwave shock method.Precise doping of nickel and precise regulation of stoichiometric ratio is realized by the high-energy microwave.We prepare a series of perovskite oxides LaNi_xMn_1-xO₃（x=0,0.2,0.4,0.6,0.8）,and investigate the effect of Ni doping on their electrocatalytic performance.The electrocatalytic OER performance of LaNi_0.8Mn_0.2O₃ has been significantly improved due to the high oxidation state of Ni³⁺and Mn⁴⁺.The prepared LaNi_0.8Mn_0.2O₃ exhibited an overpotential of 369 m V and a Tafel slope of72.9 m V·dec^-1 under alkaline conditions.