Hydrothermal Synthesis Of Nickel-iron Layered Double Hydroxide And Its Catalytic Performance For Oxygen Production From Water Electrolysis

Compared with fossil fuels,hydrogen energy is a clean energy.It has the advantages of high energy density,high calorific value,environmental friendliness,and renewable energy.Hydrogen production by electrolysis of water is a clean,efficient and sustainable hydrogen production method,but its energy consumption is too large,mainly because the kinetics of the anode oxygen generation reaction（OER）is slow.Although noble metal catalysts such as Ru O₂ have high activity for OER,it is difficult to achieve large-scale applications due to their high price and low reserves.At present,nickel-iron layered double hydroxide（NiFe LDH）has attracted people’s attention for its excellent OER electrocatalytic activity,but its electrocatalytic mechanism is still controversial,which hinders the further improvement of its catalytic performance.In this paper,a hydrothermal method was used to synthesize NiFe LDH,and its growth mechanism was systematically studied,as well as the effects of hydrothermal time and temperature on its formation process and OER catalytic performance.This is of great significance to the development of inexpensive and efficient non-noble metal-based OER catalysts.The experimental results show that the hydrothermal time has a significant effect on the phase and morphology of NiFe LDH.The core-shell characteristics of NiFe LDH can be divided into three main stages in the hydrothermal process,namely the formation stage,the development stage and the perfection stage.In the process of morphological evolution,the ratio of Ni:Fe in the radial direction of the nanospheres is not uniformly distributed.An amorphous iron-rich nucleus is first formed in the system,and then the Ni-rich components gather outside the nucleus to form NiFe LDH nanoflowers.In the hydrothermal process,the iron-containing species in the inner core continuously diffuses outward,causing the core to be continuously eroded to form a hollow structure.This hierarchical core-shell structure provides ideal nanopore channels and electrocatalytic active sites for the catalyst.The NiFe LDH-12h sample showed excellent OER electrocatalytic performance.Itsη₁₀ is only 245 m V,Tafel slope is only25.11 m V·dec^-1,and it can still maintain good stability after 3000 cycles of CV cycle test.Its performance far exceeds Ru and Ir-based precious metal catalysts.Increasing the hydrothermal temperature will accelerate the conversion of NiFe LDH to spinel phase Ni Fe₂O₄,resulting in a significant decrease in OER catalytic performance and cycle stability.In addition,reducing the concentration of NH₄F and using ferrous chloride instead of ferric nitrate as the iron source will cause changes in the morphology of NiFe LDH and adversely affect the catalytic performance of OER.In order to improve the conductivity of the catalyst,the conductive material Super P is introduced.To prevent the direct contact of Super P and the nickel-iron salt solution from affecting the nucleation and subsequent growth of NiFe LDH,the high-activity NiFe LDH@Super P composite OER catalyst can be successfully synthesized by pre-hydrothermal treatment.The preferred synthesis conditions are as follows:the pre-hydrothermal time is 2 h and the addition amount of Super P is 0.05 mg.At this time,the NiFe LDH nanoflower microspheres develop well and grow in situ on Super P.The OER catalytic performance of the composite NiFe LDH@Super P is excellent.