Preparation And Electrochemical Performance Of Transition Metal Sulfide/Oxide Supercapacitor Electrode Materials

With the increasing energy demand and the urgent need for sustainable energy technology,supercapacitors（SC）,as a basic electrochemical storage technology in renewable energy,can effectively narrow the gap between batteries and traditional capacitors.A lot of research has been done on transition metal oxides（TMOs）,transition metal sulfides（TMS）and their composite electrode materials to explore their value in the field of supercapacitors.However,these materials still have certain limitations,including low electrical conductivity,large ion transport resistance,and slow reaction rates.The above limitations hinder the electrochemical performance of these materials in energy storage applications,and people are committed to developing new electrode materials to improve the energy density,power density and accelerated charging of SC.This paper uses the heterostructure composite of Co-doped MoS₂,Gd-doped Co S_1.097,and Co₃O₄nanoparticles uniformly dispersed and grown in discrete g-C₃N₄ nanosheet clusters,combined with first-principles simulation calculations,to study three Energy storage characteristics of high-performance capacitors of electrode materials and their physical mechanisms.The specific research results are as follows:1.The sheet-like structure of MoS₂ and Co-doped Mo_1-xCo_xS₂ was synthesized through an autonomous gas-liquid deposition device combined with thermal treatment.Co atoms were doped in the crystal lattice,replacing Mo atoms and forming S-Co bonds with S atoms.As the doping amount of Co atoms increased,the discharge specific capacitance first increased and then decreased.At current densities of 1,5,10,20,and30 A/g,the corresponding specific capacitance values of Mo_1-xCo_xS₂（x=3.13%）electrode materials were 2183.1 F/g,2041.7 F/g,1846.2 F/g,1585.2 F/g,and 1217.7F/g,respectively.At a current density of up to 30 A/g,it exhibited a high specific capacitance value of 1217 F/g,which far exceeded many reported materials.At a current density of 1 A/g,the Mo_1-xCo_xS₂（x=3.13%）electrode material showed a high specific capacity retention rate of 94%and a coulombic efficiency of 99%after 10000charge-discharge cycles.2.First-principles calculation analysis indicates that in the Mo_1-xCo_xS₂ system,the Co-d and S-p orbitals merge to create a localized impurity energy level close to the Fermi level.This combination effectively narrows the bandgap,facilitating the transition from an indirect bandgap semiconductor to a direct one.Such a shift significantly improves the electrode material conductivity,thereby increasing the supercapacitor’s charge and discharge rates.As a result,the charge storage capacity of the Mo_1-xCo_xS₂ electrode is enhanced.Further,differential charge density analysis shows that throughout the charge and discharge cycles,electrons predominantly accumulate in the micro-region established by the S-Co bonds.The introduction of Co doping generates new active sites,raising the charge storage density and bolstering the Mo₃₁Co₁S₆₄ electrode material’s ability to store charges.3.Through the self-built gas-liquid deposition device,Co S_1.097 and Gd-doped Co_1-xGd_xS_1.097 nanoparticles were synthesized.Gd atoms were doped in the crystal lattice,replacing Co atoms and forming Gd-S bonds with S atoms,explaining the growth mechanism of Co_1-xGd_xS_1.097.At a current density of 1 A/g,the specific capacitance increased first and then decreased with the increase of Gd atom doping amount.When Co_1-xGd_xS_1.097（x=2.02%）was used,the specific capacitance reached the maximum.At different current densities of 1,5,10,20,and 50 A/g,the corresponding specific capacitance values of Co_1-xGd_xS_1.097（x=2.02%）electrode material were 1981.6 F/g,1526.4 F/g,1430.1 F/g,1004.18 F/g and 95 F/g respectively.After 10000 charge-discharge cycles,it showed excellent specific capacity retention rate and high coulombic efficiency,with the specific capacity retention rate maintained at about 92%and coulombic efficiency almost stabilized at 99%.4.First principles calculations reveal that in the Co_1-xGd_xS_1.097 material,hybridization occurs between S-p and Gd-f orbitals,leading to significant orbital splitting near the Fermi level.This process generates numerous new unoccupied impurity energy bands.Such splitting eliminates spin degeneracy,thereby enhancing the electrode materials cycle life.Moreover,these unoccupied impurity energy levels have the capacity to store a substantial amount of charges.Doping Co S_1.097 with Gd ions not only increases the charge storage density but also improves the chemical stability of the material.5.Through in-situ deposition and decomposition methods,the self-assembly of g-C₃N₄/Co₃O₄ heterostructures was achieved,effectively controlling the uniform dispersion and growth of Co₃O₄ nanoparticles on both sides of discrete g-C₃N₄nanosheet clusters,explaining the growth mechanism of g-C₃N₄/Co₃O₄ heterostructures.g-C₃N₄/Co₃O₄ possesses both electric double layer and pseudocapacitive properties,with corresponding specific capacitance values of 2662 F/g,2216 F/g,1750 F/g,1500F/g,1320 F/g,and 1260 F/g at different current densities of 1,2,5,10,and 50 A/g.After assembly into a device,the power density was 749.86 W/kg and the energy density was 128 Wh/kg.When the power density was 16850 W/kg,the energy density was 62.5 Wh/kg.After 6000 cycles of charging and discharging tests,the capacitance retention rate was 90%.6.First-principles calculation analysis reveals that the g-C₃N₄/Co₃O₄heterojunction material predominantly forms Co-N ionic bonds,creating a heterojunction characterized by broken interface spatial symmetry.The 3d orbital electrons of Co,alongside the p orbital electrons of N and C-p orbital electrons,establish a heterogeneous polarization interface through direct and super-exchange interactions.This interface leads to high-density spin-orbit hybridization,resulting in an increase in quantum capacitance and facilitating high-capacity energy storage within the g-C₃N₄/Co₃O₄ heterostructure.The material unique electronic structure endows it with superior electrochemical energy storage capabilities.