Preparation And Electrochemical Properties Of Transition Metal Sulfide Nano-materials

In recent years,the research of transition metal materials have attracted much attention in the fileld of energy conversion and storage due to their abundant storage,low prices and excellent performance.Therefore,the design and preparation of transition metal materials provides a direction for energy conversion and energy storage.Herein,In this work,a series of transition metal sulfide materials were synthesized by stepwise hydrothermal method,low-temperature sulfuration,and the control of morphologies.The performance of hydrogen evolution reaction?HER?,oxygen evolution reaction?OER?,overall water splitting and capacitance of these prepared materials were investigated systematically.We expect that this work will provide a new direction for the preparation of functional materials and their performance optimization.The content of this work includes four aspects:1.A core-shell NiS@CoS@CC catalysts with abundant heterointerfaces evenly grown on carbon cloth was synthesized via a facile stepwise strategy.Benefiting from the strong interfacial coupling effects between NiS and CoS,abundant NiS@CoS heterogeneous interfaces active sites,highly conductive CC substrate,and the unique core-shell heterostructures of nanosheets wrapped with nanowires.By adjusting the size of the core in the core-shell structure,the optimal NiS@CoS@CC(the molar ratio of Co²⁺:Ni²⁺is 1:1)electrocatalyst exhibited superior HER electrocatalytic activity.The extremely low overpotentials of only 30 mV is achieved at a current density of 10 mA cm^-2 with Tafel slope of 97 mV·dec^-11 and excellent durability during 1000 continuous CV and the chronopotentiometry curves for 20h.This work demonstrated that the as-prepared heterostructured NiS@CoS@CC electrocatalyst is a promising candidate for noble metal catalyst?Pt/C?to the HER.2.A sheet-like Co?OH?₂@NiS material with a 3D porous structures grown on Ni foam?Co?OH?₂@NiS@NF?were prepared by a hydrothermal and subsequent electrodeposition strategy.The as-prepared Co?OH?₂@NiS@NF electrocatalyst can be used directly as a working electrode for overall water splitting in alkaline electrolyte solutions.Due to the positive synergy,as well as the abundant heterointerfaces,and the sheet-like structure with a large number of porous,the Co?OH?₂@NiS@NF electrode demonstrates remarkable electrocatalytic activity for hydrogen evolution reaction and overall water splitting reaction.In the three-electrode system,the Co?OH?₂@NiS@NF electrode could afford a current density of 10 mA cm^-2 at the overpotential of 69 mV for the HER with Tafel slope of 125 mV·dec^-1 and ECSA value of 37 mF cm^-2 with an slightly changed current density by the chronopotentiometry curves for 24h.Moreover,the two-electrode electrolyzer with Co?OH?₂@NiS@NF as both cathode and anode achieved a current density of 10 mA cm^-2 at a cell voltage of 1.53 V with a superior electrochemistry durability by the chronopotentiometry curves for 72h.3.A rectangular spongy-like porous heterostructure NiS/CoS/CC-3 multifunctional electrocatalyst is designed and synthesized through a similar three-step hydrothermal method.Different from the previous work?the thickness of the core is changed but the thickness of shell does not change?,in this work,the thickness of shell is changed by adjusting the molar ratio of Ni²⁺in the second step.The optimal NiS/CoS/CC-3(the molar ratio of Ni²⁺:Co²⁺is 3:1)electrode exhibits excellent electrocatalytic performances for hydrogen evolution reaction,oxygen evolution reaction,and overall water splitting reaction.The NiS/CoS/CC-3 electrode in the three-electrode system can afford a current density of 10 mA cm^-2 at overpotential of 102 mV for the HER and a current density of 40 mA cm^-2 at 296 mV for the OER,respectively.Moreover,the two-electrode electrolyzer with NiS/CoS/CC-3 as both the cathode and anode catalyst in alkaline solution achieves a current density of 10 mA cm^-2 at a cell voltage of 1.57 V.Meanwhile,the electrolyzer can produce a constant stream of H₂ and O₂ bubbles at a current density of 10 mA cm^-2 under a cell voltage of 1.57 V with the chronopotentiometry curves for 72h.The abundant heterointerfaces between NiS and CoS under appropriate ratio and fluffy spongy-like structure has a significant effect on the catalytic performance.The results demonstrate that a proper interfacial modulation of heterogeneous catalysts is a promising strategy for fabricating low-cost,high activity and stable catalysts for overall water splitting,photocatalysis,CO₂ reduction and other catalytic reactions.4.In this paper,CoNi₂S₄@CC composite with ultrafine CoNi₂S₄ nanowire vertically grown on carbon cloth was synthesized by a convenient two-step hydrothermal method.The obtained CoNi₂S₄@CC as a binder-free electrode exhibits excellent electrochemical capacitance performances.The specific capacitance is reached up to 1872 F g^-1 at 1 A g^-1 in the three-electrode system.Furthermore,a battery-supercapacitor hybrid device is fabricated by the CoNi₂S₄@CC as positive electrode and porous carbon nanosheets derived from wood fungus as negative electrode.The as-fabricated CoNi₂S₄@CC//PCNS device also shows a high energy density 37.2 Wh kg^-1 at a power density of 750 W kg^-1 and a superior cycle stability?the capacitance retained 97.6%of the initial after 10 000 cycles?.Furthermore,an LED indicator can be lighted by two ASC devices.These results further demonstrate that the as-fabricated composites on carbon cloth is an effective strategy to achieve the high-efficient energy storage device.