Research On The Construction Of Transition Metal Compound Heterostructure And The Mechanism Of Energy Storage And Conversion

Nowadays,the pressure on society's energy sources is increasing.Traditional fossil energy sources are stretched with the expanding needs,and a series of environmental pollution problems caused by fossil energy sources have also received attention from countries around the world.It is therefore imperative to develop new,sustainable supplies with no pollution or less harmful pollution.As an emerging energy storage device,lithium-sulfur batteries are among the best,because of their high energy density,theoretical specific capacity,and affordable price,they are important candidates to meet the needs of human life.Hydrogen is also an emerging energy source.As the reaction product is water,it meets the pollution-free conditions of new energy sources and has considerable development potential in the future.Both involve the electrochemical part,and how to promote the catalytic conversion of the reaction in the electrochemical process is one of the research directions today.Heterostructure materials have performed well in the fields of energy and catalysis.By designing the phases of the heterostructured materials and synthesizing the interfaces,the transport and conversion of electrons or ions can be accelerated.Heterogeneous structures of transition metal compounds are synthesized through the plasticity of transition metals,which theoretically has excellent catalytic effect on the electrochemical part.The main purpose of this thesis is to synthesize heterostructures of transition metal compounds and study the mechanism of their catalytic conversion.The main contents of this paper are as follows:?1?Study on MnP₄/Mn₃O₄ heterostructure for cathode performance of lithium-sulfur batteries.In this paper,we first prepare nitrogen-phosphorus co-doped porous carbon,and synthesize MnP₄/Mn₃O₄ heterostructure?MMH?in situ using phosphorus existing on porous carbon.This method of phosphide synthesis effectively solves that the traditional methods are difficult to control,complex and toxic.The prepared MMH/C has a large specific surface area and porosity.It benefits from a special heterostructure interface and has rich active sites,which can effectively alleviate the volume expansion effect during the charge and discharge process.In the two phases of the heterostructure,Mn₃O₄ shows strong adsorption of polysulfides,and the phase has good diffusion performance,and can fully exert its catalytic conversion effect after being transferred to MnP₄.The two cooperate and assist each other,jointly alleviate the adverse effects of the shuttle effect.The excellent electronic conductivity of MMH/C sulfur carriers helps to improve the polarization phenomenon and the rate performance.Excellent discharge specific capacities of 1410 and 804 m Ah g^-1 were obtained at 0.1 and 2 C,respectively.After 1000 cycles at 0.5 C,the capacity attenuation of each cycle is only0.041%,showing excellent stability.This provides new ideas for future research on lithium-sulfur batteries and other energy storage devices.?2?Pd@MoO₃ heterostructure containing atomic Pd nanoparticles for electrocatalytic and photocatalytic hydrogen evolution.Here we use a simple hydrothermal method and a hydrogen reduction method to prepare a Pd@MoO₃ heterostructure,in which the Pd nanoparticles reduced by MoO₃are confined in the nanosheet,and there are also monolayers and Pd substitution site for the atom on the nanosheet.This improves the problem that the active sites of traditional two-dimensional nanosheet materials are located at the edges,and there are a large number of active sites at the special heterogeneous interface of Pd and MoO₃.The Pd@MoO₃ heterostructure has a very large electrochemically active surface area,and it performs well in hydrogen evolution reactions.Only 71 m V of overpotential is required to generate a current density of 10 m A cm^-2.The Tafel slope in a 0.5 M H₂SO₄solution is extremely low,which is only 42.8 m V dec^-1.Moreover,the photoresponse of the Pd@MoO₃ heterostructure is about 3 times higher than that of the MoO₃nanosheet.This design idea is expected to be applied to other catalysis,such as nitrogen reduction,carbon dioxide reduction,etc.