Research on Hydrogen Evolution Performances of Nickel-Based Chalcogenides Self-Supported Electrodes

Author:Jing Feng

Supervisor:wang shuai

Database:Doctor

Degree Year:2019

Download:171

Pages:142

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With the increasing demand for energy and the growing environmental crisis,the large-scale hydrogen production from water electrolysis is highly anticipated.At present,platinum-based materials still maintain the optimal hydrogen evolution activity,but the high cost and limited earth reserves greatly suppress their widespread application.Therefore,the development of a highly efficient and inexpensive non-precious metal-based hydrogen evolution catalysts is the key to further realize the practical application of large-scale electrolytic water hydrogen production.Compared to the powder catalysts,self-supported catalysts need neither complex film-forming process nor expensive conductive polymer binders.Meanwhile,the self-supported catalysts often have a larger specific surface area,faster electrolyte diffusion,gas release rates,and higher stability.More importantly,it is easier to construct a hierarchical structure according to different needs.In view of this,this thesis focuses on the construction and characterization of nickel-based chalcogenides self-supported electrodes,and their application in the field of electrocatalytic hydrogen evolution is also systematically studied.We have studied the transition metal nickel-based self-supported electrolyzed water electrodes within four aspects:construction of self-supported electrodes,structural regulation and characterization,electrolyte pH range and catalytic activity.The research contents are as following:1.The multiphase nickel sulfides/nickel foam(m-NiSx/NF)self-supported electrode has been successfully synthesized by a one-step sulfidization of commercial Ni foam at a low temperature.The effects of the amount of sulfur powder on its surface morphology,composition and electrocatalytic performance were also analyzed in detail.The results show that the dynamic balance of the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)can be achieved when the amount of sulfur powder is 0.5 g.Additonally,the m-NiSx-0.5/NF electrode also exhibites excellent bifunctional electrocatalytic activity and stability for overall water splitting.The m-NiSx-0.5/NF exhibits outstanding electrocatalytic activity with a relatively low cell voltage of 1.46 V to reach the current density of 10 mA cm-2 in 1.0 M KOH,and can maintain the excellent catalytic activity at least 13 h.2.On the basis of the above research,the relationship between temperature and composition of nickel sulfides was discussed in detail.The results demonstrate that the sulfidization product is multiphase nickel sulfides(m-NiSx/NF,components are Ni3S2,NiS2 and NiS)with the sulfidization temperatue is between 300-350oC;in the temperature range of 400-600oC,the sulfidization product is double-phase nickel sulfides(d-NiSx/NF,components are NiS2 and NiS);in the temperature range of 650-750oC,the sulfidization product is single-phase nickel sulfide(NiS/NF,components are NiS).In addition,the electrochemical performances are closely related to their structural compositions:under the same experimental conditions,the optimized hydrogen evolution performances of m-NiSx/NF,d-NiSx/NF and NiS/NF electrode are in the order of m-NiSx/NF>d-NiSx/NF>NiS/NF.3.In view of the instability of the above materials in acidic solutions and the diversity of pH requirement of the electrolyte solution for HER in practical applications,a self-supported NiS2 electrode,which has the similar center structure of hydrogenase,was constructed.The microstructure of NiS2 was further regulated by doping with N atoms.The obtained N-NiS2/CF electrode exhibits excellent electrocatalytic activity in both acidic and alkaline medium.To drive the current density of 10 mA cm-2 in 1.0 M KOH and 0.5 M H2SO4,an overpotential of 95 mV and 162 mV is needed,respectively.Besides,the N-NiS2/CF electrode can maintain the superior catalytic activity at least 20 h in both acidic and alkaline solutions.4.As a family element of S,the electronegativity difference between Se(with an electronegativity of 2.424 eV)and H(with an electronegativity of 2.300 eV)is less than the electronegativity difference between N(with an electronegativity of 3.066 eV)and H,indicating that the adsorption of hydrogen is more easily to occur on the surface of N-NiSe2 during the hydrogen evolution process.Based on this,the N-doped NiSe2/NF self-supported electrode has been constructed via one-step thermal selenization Ni foam under the ammonia atmosphere.The obtained N-NiSe2/NF electrode exhibits superior catalytic activity and stability for HER in alkaline medium,only an overpotential of 86mV is needed to afford the current density of 10 mA cm-2 in 1.0 M KOH.DFT calculations reveal that theΔGH*value of the N-NiSe2 is relatively close to the ideal H adsorption free energy.In addition,it also reveals that the N-NiSe2 has lower water adsorption energy(ΔGH2O*)than NiSe2,confirming that the initial catalyst-H2O is more favorable to occur on the surface of N-NiSe2,thus accelerating the HER.Moreover,the N-NiSe2/NF electrode also exhibited excellent HER performance in both 0.5 M H2SO4and 1.0 M PBS solution,to drive the current density of 10 mA cm-2,the overpotential of102 mV and 206 mV is needed respectively.