Preparation Of Nano-layered Nickel-iron Hydroxides By Controllable Crystallization And Their Electrochemical Performance

Growing energy demand and environmental awareness promote the development of efficient and environmentally friendly energy conversion and storage technologies.Among them,hydrogen production from electrolyzed water is very attractive and attracts more and more attention.The key to this renewable energy technology is accelerating the oxygen evolution reaction(OER),but due to its slow kinetics and high overpotential,it is often more challenging in practical applications.In this paper,we have prepared Ni-Fe LDHs by a novel and scalable complexation crystallization method and systematically studied the effect of different nickel-iron ratio and carbonate content on its OER performance,and on this basis,the in-situ growth method was proposed,the essay will summarized as follows:1.We adopt a mild controlled complexation crystallization method to prepare ultra-thin nano-Ni-Fe LDHs sheets as an efficient OER catalyst,and the results showed that the best OER performance is Ni-Fe LDHs with Ni:Fe atomic ratio of 15%in 1 mol L-1 KOH solution.Its overpotential and Tafel slope were,216 mV and 37 mV dec-1,lower than that of 20%Ir/C(330 mV and 130 mV dec-1)respectively at a current density of 10 mA cm-2.Furthermore,after the 15 h galvanostatic polarization experiments,the curve remains stable,which shows excellent stability and durability.In addition,we also conducted an amplification experiment,though the synthetic scale was magnified 20 times,both samples have curves almost overlapping each other,and the sample produced at large scale shows almost the same or even a little better durability,slightly lower polarization and more flat voltage at 20 mA cm-2,compared with the small-scale sample.All the above comparison results indicate that the complexation-precipitation method is scalable.Therefore,this method provides a reliable way for the industrial production of new oxygen evolution catalyst.2.In order to study the effect of carbonate insertion on the OER properties of Ni-Fe LDHs,Ni-Fe LDHs with different contents of carbonate intercalation synthesized by the above method based on the Fe content of 15%.It found that the intercalation of carbonates increased the interlayer spacing of materials and the OER properties were different.The results show that when the molar ratio of OH-/CO32-is 4:1,the obtained material has better OER performance,the oxygen evolution overpotential was 323 mV at a current density of 20 mA cm-2,with a tafel slope of 22 mV dec-1 less than 15%Fe sample without carbonates and commercial IrO2.Moreover,at higher current densities,the polarization durability is longer.3.We adopt a controlled complexation crystallization method growing Ni-Fe LDHs nano-flakes directly on the foam nickel(NF),in the process,Ni-Fe LDHs/NF electrodes with different loadings obtained by controlling the amount of Ni-Fe added dropwise.The experimental results showed that the electrode with amount of 3 mL exhibited the lowest overpotential and Tafel slope of 245 mV and 27 mV dec-1 at a current density of 10 mA cm-2,and the polarization curve after 47 h can still be stable,which is better than the same conditions with the 3D nickel foam and commercial Ir02 electrodes.This study not only provides an efficient and durable catalyst for the electrolysis of water system,but also opens a new idea for the structural design of NiFe-based electrocatalysts.