Designation,Synthesis,and Application Of Novel Two-Dimensional Metal/Sulfide Catalysts

With the rapid growth of global energy consumption,traditional fossil energy sources are challenged as never before,so it is of great importance to design efficient catalytic materials,energy storage materials,etc.Among many material systems,ultrathin two-dimensional materials,with unique structural and electronic properties,have been widely used in new-energy fields.In this thesis,we designed novel Ⅱ-B sulfide 2D materials and metal/sulfide composite 2D materials,carefully characterized the atomic and electronic structures of 2D materials,and applied them to nitrogen reduction electrocatalysis,oxygen reduction electrocatalysis,and zinc ion battery energy storage.The catalytic activity and cycle stability are significantly improved.At the same time,advanced transmission electron microscopy and synchrotron X-ray techniques are adopted to analyze the intrinsic mechanism of the excellent performance of the materials,the obtained research advances are as below:1.Theoretical predictions indicate that transition metals at the edge of the periodic table,such as Zn and Cd,exist only at a low+2 valence,but that metal disulfides,which would otherwise be impossible to exist,can be made possible by the valence change of sulfur atoms.By combining in-depth theoretical predictions with a special metal-template-confined chemical vapor deposition technique,stable,monolayer 1-T phase Zn S₂ disulfide was designed and prepared,and their atomic and electronic structures were characterized by spherical differential electron microscopy,scanning tunneling microscopy,and X-ray synchrotron radiation.It was found that the novel 1-T structure of Zn S₂ has unique electron-deficient character and exhibits unusual special valence states.This work provides a new idea to synthesize the"non-naturally-existent"metal disulfides.2.High-performance ammonia production was realized using monolayer 1-T Zn S₂nanosheets under alkaline conditions,and ammonia conversion efficiency of 15%and ammonia production rate of 27μg·h^-1·cm^-2were achieved at an operating potential of-0.3 V.A series of comparative experiments were designed to demonstrate that the efficient ammonia production performance originates from the unique electronic structure of 1-T phase Zn S₂.Furthermore,advanced in-situ ambient pressure AP-XPS and DFT adsorption energy calculations confirmed that the electron deficient property of Zn S₂ can adsorb and activate nitrogen more efficiently,thus significantly enhancing the selectivity of the nitrogen electroreduction reaction.3.An ultrathin Zn S/Zn/Zn S metal-sulfide composite nanosheet with sandwich structure was synthesized and used as zinc ion battery anode to realize a new highly stable,dendrite free zinc-air battery.The structural evolution of the metal/sulfide composite nanosheet anode during the charging and discharging process as well as during the long cycle has been studied in detail using advanced electron microscopy techniques.It was shown that the sulfide layer on the surface of the nanosheets remained stable during the charging and discharging process,which effectively promoted the uniform deposition of Zn ions.Combined with electron microscopy and finite element calculations,it is confirmed that the stable,dendrite free ultrathin sandwich structure arises from the homogenization of the surface polycrystalline sulfide layer and the atomically flat surface of the nanosheets.4.A high-entropy doped Pd-based ultrathin metal nanosheet was synthesized for catalyzing efficient and stable electrocatalytic oxygen reduction reaction.On the basis of comprehensive analysis,it was found that the high entropy doping leads to a significant compressive stress in the Pd nanosheets,which improved their electronic structure and oxygen adsorption properties.It was further confirmed by AP-XPS that the high entropy doped Pd nanosheets facilitated the oxygen reduction reaction（ORR）kinetic process.