Studies On The Preparation And Electrocatalytic Performance Of Cobalt-based Layered Double Hydroxides Nanomaterials

Hydrogen energy has been considered to be the one of the most promising new energy in the 21st world because of the advantages of direct storage,high energy density,abundant resources and non-polluting combustion products.At present,electrochemical water splitting is an important method of hydrogen production.However,the high OER overpotential greatly limits the efficient operation of water splitting due to the slow kinetic OER process and four electron transferring procedures.Therefore,it is an urgent task to design a stabilized and low cost electrocatalysts with high efficiency.Excellent electrocatalysts generally need to have the characteristics of larger specific surface area,stronger conductivity and richer active sites.In this paper,we use the layered double hydroxides as the research object to prepare two types of catalysts and perform in-depth analysis of their performance.1.In this work,a novel NiFe-NiCoO2 hollow polyhedron was obtained by a reduction reaction of the NiFe(CN)6-intercalated NiCo-LDH.To the best of our knowledge,this is the first time to synthesis the metal-based anion intercalated NiCo-LDH using the one-step ion exchange method.The hollow nanostructure which consists of plentiful nanoparticles can provide abundant mass transport channels to increase the contact area of the material with the electrolyte,the NiCoO2 is an active site of electrocatalyst for OER and NiFe alloy for HER,the presence of the alloy also can improve the conductivity of the material.The NiFe-NiCoO2 exhibited excellent performance for OER and HER,and the material also have prominent electrochemical durability.This work provides a new approach for the design of highly efficient water splitting catalysts for sustainable energy conversion and storage.2.In this work,ZIF-67 was used as template to directly obtain the hollow dodecahedron NiCo-LDH and CoCo-LDH.Than we have explored the influence of the amount of additional metal salt on the morphology and structure of LDHs and tested the OER performance of NiCo-LDH and CoCo-LDH.The prepared NiCo-LDH(X=2)and CoCo-LDH(Y=7.5)have a unique hollow structure and a large specific surface area,which is beneficial to the exposure of electrocatalytic active sites,and can also increase the contact area of the material with the electrolyte.The NiCo-LDH(X=2)exhibited excellent performance with small overpotential(311 mV),low Tafel slope(72.2 mV/dec)for OER,the CoCo-LDH(X=2)exhibited excellent performance with small overpotential(290 mV),low Tafel slope(69.9 mV/dec)for OER.The overpotential of the oxygen evolution reaction of the NiCo-LDH and CoCo-LDH were much lower than that of commercial Ir/C catalyst.At the same time,both NiCo-LDH and CoCo-LDH exhibited excellent stability during the reaction.