Study On The Modification Of Lithium-ion Electrode Materials And The Application Of V_xM_y(M=Se Or C) In Hydrogen Evolution Reaction

Energy is the foundation of social development and economic growth.However,the approaching depletion of traditional fossil fuel pushes us to develop new and renewable energy sources.The development history of new energy technology indicates that lithium ion battery and water electrolysis are the most prospective methods in energy storage and transformation.However,with the continual enlarging of application range of lithium ion battery,people are calling for more power battery with high energy density and watt density,and the conventional electrode materials can not meet the need of market.Besides,the conventional catalyst for hydrogen evolution reaction is noble platinum.Because of its high costs and low reserves,searching for non-noble metal catalysts with high catalytic activity and low cost has been the research hotspots in the field of electrocatalysis.At present,there are many problems with lithium ion battery electrodes,such as poor structural stability,low electronic conductivity,huge volume change during charge-discharge process,and low lithium ion diffusion rate.In this paper,we adopted physical and chemical method,such as surface coating,ion doping and crystal regulation,to improve the performance of electrode materials.Besides,we fabricated two non-noble metal catalysts（V₂Se₉ and V₈C₇）for hydrogen evolution reaction.In addition,we took two approaches（conducting polymer coating and crystal regulation）to improve the catalytic activity of catalysts.The specific research contents of this paper are as follows:（1）Low crystal-mismatch strategy has been applied in the synthesis of ions-doped LiCoO₂ materials and a good success of single crystal property has been achieved between the precursor and final sample for the first time.The hexagonal LiCo_0.8Al_0.26O₂nanomesh possesses several advantages in morphology and crystal structure,including mesoporous structure,single crystal,atomic even distribution,high exposing surface area as（100）and shortened Li ions diffusion distance.All the merits are very beneficial to the application in Li ion batteries cathode,for example,accelerating Li ions diffusion rate,improving the Li ions shuttle between the LiCo_0.8Al_0.26O₂ nanomesh and electrolyte as well as reducing the Li ions capacitive behavior while lithium-ion intercalation.（2）We proposed a novel and green strategy to convert crop stalks waste into hierarchical porous carbon composites for electrode materials of lithium-ion batteries.In the method,environmentally friendly crop stalks,was used as a porous template for large-scale production of high performance electrode materials（for example,LiFePO₄/C,LiMnPO₄/C,Li₂FeSiO₄/C and TiO₂/C）for lithium ion batteries.Owing to the large surface area,porous structure and small size of the functional particles,the nanocomposites manifest excellent electrochemical performance.（3）We reported V₂Se₉ nanosheet arrays exposed with the highly active（100）facet as a new efficient catalyst for HER.The highly active but thermodynamically instable（100）facet was converted from V₂O₅ based on a low crystal-mismatch strategy.Furthermore,conductive PEDOT acting as co-catalyst further contributed to the redistribution of charge and reduction of hydrogen adsorption energy.Due to the strong synergistic effect between V₂Se₉ and PEDOT,the resulting material,exhibited the best electrocatalytic performances among selenide catalysts,for example,small overpotential of 72 mV at 10 mA cm^-2,low Tafel slope of 36.5 mV dec^-1,and outstanding durability.Simultaneously,density functional theory computations proved that the adsorption free energy of H*(△G_H*)for V₂Se₉@PEDOT NSs/NF（0.09eV）is comparable to that of Pt（around 0.09eV）.（4）We reported a novel platinum-like,double-deck carbon coated V₈C₇ nanofabric with the highly active（110）facet exposed as a new efficient HER electrocatalyst.The single-crystal V₈C₇ nanofabrics were designedly fabricated based on a low crystal-mismatch strategy and confinement effect of double-deck carbon coating.Besides,electrochemical tests and theoretical simulation indicated that the metallic character of V₈C₇,high-activity of exposed facet,and low barrier energy for water dissociation could contribute to highly catalytic activity of HER.Impressively,the HER performances of V₈C₇ nanofabrics could be comparable to those of Pt at an all-pH environment.This work provided a blueprint for exploring new-type platinum-like catalysts for various energy conversion systems.