Study On Charge Storage And Electrocatalytic Performance Of High Loading Co-Ni Sulfide Electrode

As an ideal energy storage device,supercapacitors have the advantages of fast charge/discharge rate,long life,high power density,and high safety.Overall water splitting is an ideal technology for producing hydrogen,which has the advantages of high efficiency,environmental protection and sustainable development.The performance of supercapacitors and overall water splitting devices depends mainly on the performance of electrode materials.Co-Ni sulfide electrode is a promising multifunctional electrode material with abundant of active sites and high conductivity.In this thesis,the study on the growth of high-loading Co-Ni sulfide electrode on the surface of conductive carbon cloth was carried out,and the capacitive performance and electrocatalytic activity of the as-obtained electrode were further optimized.The main achievements are as follow:1)The growth of CoNi₂S₄ nanoparticles with high mass loading(16.09mg·cm^-2)on the surface of carbon cloth（CC）was achieved by by a two-step hydrothermal sulfuration.The introduction of ethylene glycol significantly improves the hydrophobicity of carbon cloth,and effectively tunes the morphology and loading mass of CoNi₂S₄ particles.The CoNi₂S₄/CC electrode with the holey characteristic provides rich active sites for electrolyte access,resulting in the enhancement of charge storage capacitance.The CoNi₂S₄electrode shows a high areal capacitance of 21.7 F·cm^-2 at 10 mA·cm^-2 and a prominent coulombic efficiency andrate performance.Furthermore,the as-assembled hybrid supercapacitor delivers a high areal capacitance of 3.16F·cm^-2,an energy density of 1.425 m Wh·cm^-2 at a power density of 9.0m W·cm^-2,and the high capacitance retention of 92.5%after 20,000 cycles.2)The CoNi₂S₄ nanoparticles with high mass loading also provides abundant active sites for surface electrocatalysts.Moreover,by soaking the CoNi₂S₄/CC in acetone,CoNi₂S₄/Co₉S₈ composite is formed.Benefiting from the structural advantages of Co₉S₈ phase,CoNi₂S₄/CC electrode shows the enhanced electrocatalytic activity.The as-soaked CoNi₂S₄/CC electrode possesses an excellent hydrogen evolution reaction(overpotential of 64 m V at 10 m A·cm^-2)and oxygen evolution reaction(232 m V at 10 m A·cm^-2)activities in 1.0 M KOH solution,lower than than those of pristine CoNi₂S₄/CC electrode（137 m V and 271 m V,respectively）.Moreover,the overall water splitting electrolyzer assembled by CoNi₂S₄/CC exhibits a low cell voltage(1.58 V@10 m A·cm^-2 and1.82 V@100 m A·cm^-2)and a high durability.3)The influence of soaking conditions on the morphology,composition and capacitive performance of the CoNi₂S₄/CC electrode is explored,which suggests a new and effective activiation strategy for Ni-Co sulfide electrode.The as-soaked CoNi₂S₄/CC electrode has a specific capacitance of 19.8 F·cm^-2(1600F·g^-1)at 50 m A·cm^-2(4.05 A·g^-1).Moreover,the assembled all-solid symmetrical supercapacitor has an area specific capacitance of 6.5 F·cm^-2 at 10 m A·cm^-2,an energy density of 1.76 m Wh·cm^-2 at a power density of 7.0 m W·cm^-2.The capacitance retention of the device was 107%after 10,000 cycles,indicating its excellent cycle stability.