Investigation On Pseudocapacitor Energy Storage Behavior Of Defect-Regulated Transition Metal Selenide

As a typical pseudocapacitive material in supercapacitor electrode materials,transition metal selenide has attracted widespread interest in the field of supercapacitor electrode materials due to its valence diversity,high electrochemical activity,and inherent metal properties.However,the problems of low intrinsic conductivity,insufficient utilization of active sites,and slow kinetics of redox reactions seriously restrict its practical application.As an improvement method on the atomic scale,defect engineering can effectively improve the local atomic structure/coordination environment of electrode materials,so as to effectively adjust the electronic structure properties,reduce the diffusion energy barrier,provide additional intercalation sites,and realize the adjustment of energy storage mechanism in the lattice.Based on this,the NiCo₂Se₄ electrode material with Se vacancy was obtained by NaBH₄ reduction treatment and P doping respectively,and the influence of Se vacancy concentration on its electrochemical performance and its mechanism were deeply explored,which provided an effective strategy for the construction of high-performance supercapacitors.The main research contents are as follows:1.The NaBH₄ driving vacancy defects strategy was uesd to construct NiCo₂Se_x electrode materials with different Se vacancies concentrations.When the concentration of NaBH₄ is 2 mol,the vacancy concentration of the electrode material is 25%.Thanks to V₂-NiCo₂Se_x electrode material at this vacancy concentration,higher specific capacity(310.8mAh g^-1,1A g^-1)and capacity retention rate（58.9%,5000 cycle）were achieved compared with untreated NiCo₂Se₄(194.7 mAh g^-1,1A g^-1).Combined with density functional theory（DFT）calculation,the effects of vacancy introduction on surface activity,OH^-adsorption and charge density were analyzed,and the influence mechanism of vacancy introduction on the performance of supercapacitors was explained.Hybrid supercapacitors（V₂-NiCo₂Se_x//AC）assembled using V₂-NiCo₂Se_x and AC provides an energy density of 76.45 Wh kg^-1at a power density of 800.06 W kg^-1.2.A safe and effective method was used to induce the generation of NiCo₂Se₄ in situ Se vacancy by P doping.The synergistic effect of P doping and Se vacancies greatly improved the supercapacitor performance of NiCo₂Se₄ electrode materials,and when the P source was100mg,the P-doped NiCo₂Se₄ sample had the smallest charge transfer resistance(R_ct=0.768Ω)and good cycle stability（5000 cycle,60.9%）,and showed ultra-high specific capacity(416.6 mAh g^-1,1 A g^-1)compared with the untreated NiCo₂Se₄ sample(194.7 mAh g^-1,1A g^-1).At the same time,combined with theoretical analysis,it is proved that the dual-effect synergy of P doping and vacancies can effectively change the electronic structure,improve the adsorption capacity of ions,and make redox reactions more likely to occur,accelerating the reaction kinetics.A hybrid supercapacitor（NiCo₂Se_x-P₁//AC）assembled with NiCo₂Se_x-P₁ and AC has 90.2%capacitance retention and 100%coulomb efficiency after 10000 consecutive charge-discharge cycles,and exhibited a high energy density of 94.6 W h kg^-1at a power density of 799.9 W kg^-1.