Salt-templated Method Synthesis Two-dimensional Transition Metal Nitrides For Electrochemistry

Clean new energy is highly desired owing to the sustaining consumption of traditional fossil fuels and the accompanying environmental issues.Hydrogen energy is one of the clean and efficient energy sources and has been attracted widely attention.Hydrogen evolution reaction?HER?is a promising strategy to generate hydrogen.However,the expensive price of current noble-metal catalysts confines the large-scale production.Therefore,exploring state-of-the-art non-noble metal electrocatalysts is the most significant task in this field.In addition,supercapacitor,as an excellent energy storage device,can provide energy constantly not affected by the external conditions.However,the poor energy density restrains its widely application.View from this insight,fabricating outstanding electrode materials which improve the energy density dramatically without sacrificing the power density and long-life span is urgently needed.Herein,we focus on synthesis two-dimensional transition metal nitrides for HER and energy storage applications.The main results are as following:?1?The 2D transition metal nitrides?MoN,V₂N,and W₂N?were successfully fabricated by salt?NaCl and KCl?template method and the as-synthesized transition metal oxides coating salts as precursor.The salt-templated method is a universal way to synthesize 2D materials even for the non-layer structure compounds.Moreover,improving this strategy to utilize the lattice match between salts and nitrides,we firstly synthesized the two-dimensional nitrogen-enriched tungsten nitride W₂N₃ nanosheets directly.?2?In order to explore the electrical properties of 2D MoN nanosheets,the first principle calculation was firstly involved which confirmed the metallic phase of the 2D MoN.Then we fabricated the micro device based on single-layered MoN nanosheet to investigate the variation of electrical conductance via temperature,which is consistent with the theoretical calculation.The 2D MoN is metallic phase material with excellent electrical conductivity.We then investigated the energy storage properties of 2D MoN nanosheets as electrode for supercapacitors.The 2D MoN demonstrated the promising energy storage property under super high sweep rate.The volumetric capacitance remains 200 F cm^-3 at 20V s^-1 in 1M H₂SO₄ electrolyte,and the highest volumetric capacitance is up to 928 F cm^-3.?3?The 2D W₂N₃ nanosheets with different contents of surface nitrogen vacancies can be synthesized by tuning the reactive temperature,which can modify the surface electrical structures of 2D W₂N₃ nanosheets.The surface nitrogen vacancies was confirmed by various tests.The 2D W₂N₃ nanosheets with different nitrogen vacancies were applied to HER as electrocatalysts.The 2D W₂N₃ nanosheets with 6.7%nitrogen vacancies showed the best HER activity(onset potential-30.9 mV,over potential-98.2 mV at 10 mA cm^-3).Furthermore,the density functional theory?DFT?was employed to catalytic mechanism of2D W₂N₃ nanosheets.The 2D W₂N₃ nanosheets with 7.5%nitrogen vacancies emerged the best hydrogen adsorption energy?0.049 eV?which is close to the 0 eV,which means the best HER property according with the experimental results.