Preparation And Electrocatalytic Water Splitting Performance Of Ni,Co,Fe Based Two-Dimensional Materials

Since the industrial revolution,people have developed many inventions and technologies.Most technologies depend on fossil energy sources.Fossil energy is non-renewable and has limited storage.Moreover,the excessive use of fossil fuels will cause pollution to the environment.Hydrogen energy is ideal energy source that can replace fossil fuels due to its advantages of environmental friendliness,cleanliness and high efficiency.Electrochemical water splitting is a promising technique to obtain highly pure H₂.The electrochemical water splitting includes two half reactions:hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The HER and OER are relatively sluggish in reaction kinetics due to multi-electron transfer process.Therefore,developing catalysts with low price,high activity and stability is the key to the development of electrolyzed water.Transition metals Ni,Coand Fe-based catalysts have attracted much attention in water splitting due to their low cost and unique electronic structure.However,the poor conductivity and stability hindered their further development and application.In this dissertation,a series of transition metal catalysts have been successfully developed through the strategies of crystal phase modulation,morphology control,heterostructure strategy and heteroatom doping.The catalysts have shown excellent performance for water splitting.The main research contents are as follows:1.We report an efficient approach to construct amorphous holey NiCoS nanosheets by using NiCo-MOF as templates.We illustrate the feasibility of this method to control the hole size and pore density in the nanosheets by altering the time of sulfidation process.Benefiting from porous 2D architecture,S-doped species,synergistic effects of Ni and Co,as well as amorphous nature,the holey NiCoS-NS exhibit low overpotential of 280 and 303 mV at current density of 10 mA cm^-2 for OER and HER,respectively.Besides,when further employed as a two-electrode electrolyzer assembly,the holey NiCoS-NS exhibits a low potential of 1.58 V at 20 mA cm^-2.2.Inexpensive and highly efficient bifunctional electrocatalysts are significant for water splitting.Herein,free-standing heterogeneous MoS₂/NiCoS nanosheets as bifunctional electrocatalysts are designed.The abundant heterogeneous interfaces in MoS₂/NiCoS,enriched holes and few-layered structure of MoS₂ can not only provide enriched active sites but also accelerate the electron/ion transfer.Consequently,the optimized MoS₂/NiCoS heterostructure achieves a low overpotential of 189 mV for HER and 290 mV for OER at 10 mA cm^-2 in alkaline electrolyte.Particularly,as a two-electrode electrolyzer assembly,the MoS₂/NiCoS heterostructure nanosheets can afford a current density of 10 mA cm^-2 at voltage of 1.50 V.3.Ce-doped FeOOH nanosheets are directly synthesized on nickel foam(Ce-FeOOH/NF)by a simple hydrothermal method.The electronic structure of the catalyst is changed by the doping of Ce.The 2D morphology of Ce-FeOOH can expose more active sites.Nickel foam with three-dimensional porous structure can not only enhance the conductivity of the catalyst but also facilitate the penetration and mass transfer of the electrolyte.As a result,the catalyst shows excellent OER performance in alkaline electrolyte.As an anode,the Ce-FeOOH/NF exhibits a low overpotential of230 mV at current density of 100 mA cm^-2.Besides,when further employs as a two-electrode electrolyzer assembly,the Ce-FeOOH/NF exhibits a low potential of 1.62V at 10 mA cm^-2.