Electrochemical Doping Control To Prepare Nickel-sulfur Compounds And Their Catalytic Performance

With the depletion of traditional fossil energy and the deterioration of ecological environment,the development of the clean,efficient and safe energy has become a global consensus.Hydrogen energy has the characteristics of non-carbon pollution and high energy density,which is expected to replace fossil energy as a new energy source.Electrolytic water can make full use of secondary energy to prepare high purity hydrogen.Platinum and Iridium are the best catalysts for electrolysis of water,but these precious metals have low reserves and highly price,which limit there widly application.Due to the rich reserves and unique electrochemical properties,nickel sulfide has many advantages in electronic transmission,which is a good catalyst used for electrolysis of water.The development and utilization of clean green energy is the focus of current energy research field.However,transportation is a common problem in the process of most clean energy utilization,such as electric energy,which requires reliable energy storage devices for mobile devices.Supercapacitors are considered to be the most valuable electrochemical energy storage devices because of their high power density,good multiplicity and long cycle life.Deep eutectic solvents?DESs?as a new green solvent has wide electrochemical window,high ionic conductivity and good thermal stability.It has great application prospects in the preparation of electrode materials.In this paper,DESs is used as solvent system to prepare nickel-based sulfide electrode materials,and the application of these electrode materials in catalytic hydrogen evolution,oxygen evolution and supercapacitor are explored.It mainly includes the following research contents:?1?Copper-supported NiS_x compounds were prepared by one-step electrodeposition in choline chloride-ethylene glycol DES?Ethaline?.The effects of their structural characteristics and catalytic properties were investigated.The results show that the growth rate of Ni in vertical direction can be changed by the introduction of S,and the morphology changes from nano-flake to three-dimensional porous spherical structure.This special porous configuration greatly increases the specific surface area of the structure and exposes more active sites.S enters the lattice of Ni in the form of doping,which regulates the electronic structure of the surface layer of Ni,which makes the charge on the surface of Ni aggregate to the surface of S,then improves the catalytic hydrogen evolution performance of the electrode material.NiS_x as the electrode material for hydrogen evolution reaction,which exhibits good performance in alkaline electrolyte under the optimed condition of S doping.The initial overpotential required for-18 mV,and a low Tafel slope is 54 mV·dec^-1.For long-term electrolysis at a constant current density of 10 mA?cm^-2,the NiS_0.25/CW can preserve its original HER activity for at least 60 h.?2?On the basis of NiS_x,Co-element is further introduced to prepare the electrochemical co-deposition of Ni,Co,S ternary compound in Ethaline to obtain nickel-based double-metal sulfide.This study found that the doping of S changed the micro-morphology of the electrode material,improving the specific surface area and the Co-doping control the surface layer electronic structure of Ni;the DFT calculation shows that Co/S co-doping changes the charge distribution of the Ni-atom surface and enhances the metallic property of the material,the adsorption energy of the electrode material in the process of HER and OER performance is optimized.The onset overpotential of HER in the alkaline electrolyte is-47 mV vs.RHE,the Tafel slope is 50 mV/dec^-1.And the onset overpotential of the OER is 250 mV.As a two-electrode electrolysis,the current density of 10 mA?cm^-2 is 1.57 V.The NiCo_xS_y/NF electrode material is assembled into a symmetrical super-capacitor device,and the energy density can reach 21.28 Wh?kg^-1 when the power density is 5 kW?kg^-1,and this material has practical application prospects.?3?A new method for preparation of Ni₃S₂ electrode material in Ethaline,was proposed to realize the in-situ transformation of the catalytic material on the collector.The Co-Ni₃S₂ electrode was obtained by introducing the Co element in the form of doping.The special nano-flake structure obtained by sulfurization,which greatly increases the specific surface area of the electrode and provides more electrochemical active sites,thus improving the capacitance performance of the electrode material.The results of DFT calculation show that the incorporation of Co atoms regulates the ability of Co-Ni₃S₂ electrode material to adsorb OH^-,and makes its adsorption energy moderate,which is more favorable for the reaction.At a current density of 5 mA·cm^-2,the electrode capacitance can reach 23491 mF·cm^-2.Using Co-Ni₃S₂ and activated carbon to assemble asymmetric capacitor,the potential application of Co-Ni₃S₂ electrode material in supercapacitor field is explored.The Co-Ni₃S₂can diliver a energy density of 247.1 Wh·kg^-1 at a power density of3.99 kW·kg^-1.