Study Of The Transition Metal Sulfides Grown On Nickel Foam Substrate For Water-splitting

Hydrogen has regarded as one of the most promising traditional energy substitutes in the 21^stcentury.It can be obtained by electrolysis water which uses the electric energy and/or thermal energy.It is a kind of energy storage material with high combustion value,zero CO₂ emission,and no pollution.Electrochemical water splitting is an effective way to convert electrical energy into hydrogen energy.However,the anodic oxygen evolution reaction of electrochemical water splitting involves four electronic processes and cathodic hydrogen evolution reaction involves two electronic processes.These result in slow kinetics.High potential is needed to overcome these obstacles,leading to seriously waste of electrical energy.The catalysts can effectively reduce the potential and improve the catalytic efficiency.At present,Pt-,Ru-,Ir-based and the other precious metal catalysts are considered to be the most efficient catalysts for water splitting.However,they are scarce and expensive on the earth,limiting their extensive use in the industry.Therefore,it is extremely urgent to find a catalyst that is earth-abundant,low-cost and efficient.In this paper,the catalysts of CoNi₂S₄/Ni,Ni₃S₂/Ni,and Ni?OH?₂/Ni₃S₂/Ni was synthesized by using a simple low-temperature hydrothermal method based on the transition metal sulfides as the main line.The research shows that these materials have a good performance for water splitting.The research contents are as follows:?1?CoNi₂S₄/Ni was prepared by using the simple two-step hydrothermal method at low temperature.The CoNi-LDH was synthesized firstly,and then the thioacetamide was employed as the sulfur source to exchange the CoNi precursor to CoNi₂S₄/Ni.The obtained CoNi₂S₄/Ni possessed a three-dimensionally lily-like morphology.The surface of CoNi₂S₄/Ni is rough and porous.The CoNi₂S₄/Ni also has great conductivity and has the similar catalytic activity center as hydrogenase.Finally,it is found that the CoNi₂S₄/Ni has good hydrogen evolution reaction and oxygen evolution reaction activity and can be used as a bifunctional electrocatalyst for overall water splitting.However,the material is difficult to large-scale prepare to meet industrial production needs.?2?A simple one-step hydrothermal sulfurization method was used to modify the nickel foam,and the Ni₃S₂ nanowires directly supported on Ni foam were synthesized?Ni₃S₂ NWs/Ni?.This material only needs to enlarge the area of nickel foam to achieve a large amount of preparation.The obtained results show that because of Ni₃S₂ NWs/Ni has a large active area and good electrical conductivity,the material is directly grown on nickel foam with nanowires structure.Therefore,the Ni₃S₂ NWs/Ni has good performance for water splitting.?3?The inner three-dimensionally trunk-like Ni₃S₂ directly grow on Ni foam was prepared.Combined with the external three-dimensional porous structure of nickel foam?3D NF?,the inner and outer three-dimensionally Ni₃S₂/NF substrate was obtained?3D-3D Ni₃S₂/NF?.In this experiment,Ni?OH?₂ was used as a material to compare the advantages of the 3D-3D Ni₃S₂/NF and the 3D NF substrate in material synthesis.Ni?OH?₂ on the 3D-3D Ni₃S₂/NF substrate was synthesized through a low-temperature hydrothermal method.The as-obtained Ni?OH?₂/3D-3D Ni₃S₂/NF has tree-like structure.The leaves are Ni?OH?₂ nanosheets,and the trunk is the Ni₃S₂.There has synergic effect between the Ni?OH?₂ and Ni₃S₂ in the Ni?OH?₂/3D-3D Ni₃S₂/NF.Furthermore,the unique tree-like structure of Ni?OH?₂/3D-3D Ni₃S₂/NF can expose more active sites and allow the efficient contact between the active site and electrolyte.Therefore,the as-prepared Ni?OH?₂/3D-3D Ni₃S₂/NF shows excellent hydrogen evolution reaction and oxygen evolution reaction activity.The results indicate that by adjusting the reaction solvent,it can obtain the 2D-3D,1D-3D and0D-3D Ni₃S₂/NF substrates,which could be applied for the different application requirements.