Designed And Controlled Fabrication Of Transition Metal Compounds And Their Efficient Application In Electrocatalytic Hydrogen Evolution Reaction

With the development of science and technology and the increasing attention that human beings have paid to the living environment,renewable energy（such as solar energy,wind energy,water energy,etc.）will gradually replace the non-renewable energy（fossil fuel）which causes serious environmental pollution.Among the renewable energy sources,solar energy and water energy etc.are usually dispersed and intermittent,time-and weather-dependent,which causes the unsustainable energy supply.However,hydrogen energy,as a clean,pollution-free energy with high energy density,can be produced and used at any time without the influence of weather change.It is expected to be the most ideal renewable energy.There are many preparation technologies of hydrogen.Among them,water electrolysis for hydrogen production has a great development prospect.The process of water electrolysis can be divided into two parts:cathode hydrogen evolution（HER）and anode oxygen evolution（OER）.It is worth noting that the electrode material is the key factor to influence the efficiency of water electrolysis.At present,the best catalyst for HER is Pt,but its broad applications for the hydrogen production are hindered by the exorbitant price.Therefore,exploring efficient,economical and stable catalysts is a significant strategy to facilitate electrochemical water splitting toward widespread industrialization.Previous researches have shown that various strategies,such as nanocrystallization,morphological control and introducing supports,could optimize the morphology,composition and surface characterisitic of transition metal compounds,further promoting the electrochemical performance.Herein,in this paper,the catalysts of cobalt telluride nanoparticles based on N-doped carbon frameworks and platinum single atoms supported by vanadium carbide have been successfully prepared through reasonable design.The morphology,composition and electronic structure of the as-prepared catalysts have been analyzed by relevant test and characterization methods.Meanwhile,their HER performance have also been evaluated and studied by theoretical calculation.The research contents can be described as follows:（1）Firstly,we synthesized ZIF-67 precursors with dodecahedral morphology by precipitation method.Then the precursor is mixed with tellurium powder and annealed in Ar atmosphere for high temperature telluride process.At different telluride temperature,we synthesized Co Te/C,Co_1.11Te₂/C and Co Te₂/C.Compared with Co Te/C and Co Te₂/C,Co_1.11Te₂/C presents the highest catalytic activity for HER and it has a much lower overpotential and Tafel slope.The results of X-ray photoelectron spectroscopy（XPS）and temperature programmed reduction（TPR）reveal the differences of surface electronic structures between Co Te/C,Co_1.11Te₂/C and Co Te₂/C.The theoretical calculation also shows that Co_1.11Te₂/C has the minimum Gibbs free energy of hydrogen adsorption(ΔG_H*=-0.1202 e V).These results discovered that changing the ratio of cobalt to tellurium can effectively adjust the d-band electronic structure of cobalt,and reducing the kinetic energy barrier of H-H bond formed on the surface of Co based materials,further improving the HER performance of the catalyst.In addition,due to the properties of porosity and large surface area,the carbon frameworks can make the loaded cobalt telluride nanoparticles expose more active sites,enhance the material transport efficiency,thus promoting the electrocatalytic performance.What’s more,in the long-term electrocatalytic process,the carbon frameworks can also improve the conductivity of the catalytic nanoparticles,avoid the agglomeration of cobalt telluride particles,and enhance the stability.（2）NH₄VO₃ nanoflake arrays were prepared via hydrothermal method on the Nikel foam.Then,the NH₄VO₃ nanobelt array was calcined in CH₄ and NH₃ atmosphere to synthesize VNC/NF.The HER activity of VNC/NF was tested in acid medium.The nanomesh structure of VNC/NF can provide a large active area,and VNC/NF itself has an electronic structure which is similar to platinum.Thus,VNC/NF shows a good catalytic activity for HER,the overpotential of VNC/NF is only 73 m V.After introducing nitrogen atom,charge transfer could occur among V,N and C in VNC/NF.Due to the strong electronegativity of N,the electrons of V atom and C atom are transferred to the surrounding N atom,resulting in the decrease of electrons in V atom.The d band centre of VNC/NF moves down,thus the V-H bond is weakened.The adsorption of hydrogen on V atom is weakened,accelerating the desorption process of adsorbed H atom from the catalyst surface and balancing the adsorption and desorption ability of VNC/NF of hydrogen.