Synthesis And Electrochemical Applications Of Nife Layered Double Hydroxides

With the pace of global economic growth,population expansion and industrialization,the limited energy reserves while climbing energy consumption have brought urgent issues to the society.Recently,the development of renewable clean energy and the reduction emission of greenhouse gases such as CO2 have gradually become the focus of research.The water splitting and CO2 electrocatalytic reduction could be effective ways to produce renewable energy.Water splitting composes hydrogen evolution reaction(HER)in anode and oxygen evolution reaction(OER)in cathode,in which the OER is a four-electron transfer process with sluggish kinetics.Therefore,it is urgent to find a stable OER catalyst with high efficiency and low price to accelerate the OER process.At the same time,the OER process also plays an indispensable role in the process of CO2 electrocatalytic reduction.Besides,it requires a higher overpotential and persistent stability.Therefore,an urgent requirement is aroused for the optimal catalyst.Commercial noble-metal catalysts including RuO2 and IrO2,have excellent oxygen evolution catalytic activities,but they are easily oxidized to RuO4 and IrO3 in the electrocatalysis process,which may weaken their catalytic stability,and the scarcity of noble metal impedes the large-scale industrial application of it as catalyst.In recent years,a large number of works have been devoted to the development and utilization of non-noble metal alternative catalysts,such as perovskite,spinel,metal oxides and transition bimetal hydroxide.The transition metal based catalysts are not only with lower price and simple synthesis process,but also possess excellent electrochemical activity in alkaline system.Among with the reported OER catalytic materials,NiFe layered double hydroxides(NiFe LDHs)shows excellent catalytic activity in OER.However,the identification of active sites in NiFe LDHs and the influence of bubble evolution during the OER process has been under study.In view of the above issues,this paper carried out research from the following two aspects:1 Based on the controllable structure of LDH laminates,we introduced Zn2+and Al3+ into NiFe LDH laminates to prepare NiFeZn and NiFeAl LDHs,respectively,and selectively etched Zn and Al by mild alkali treatment to obtain Ni-O-Fe and Ni-O-Ni atomic defects in treated NiFe LDH with high oxygen evolution activity.The electrochemical test was carried out in the 0.1 M KOH,the defective NiFeZn LDHs with Ni-O-Fe defects showed enhanced the OER activity with onset potential as low as 190 mV.However,the defective NiFeAl LDHs with Ni-O-Ni defects had a limited improvement in catalytic activity compared with the NiFeAl LDHs,while still worse than that of NiFe LDHs.Combining with the DFT plus U calculation,the ultrahigh OER performance of D-NiFeZn LDH has been correlated to the exposed Ni-O-Fe active sites.2 NiFe LDHs nanoarray electrodes were prepared by hydrothermal method.Different types of ionic surfactants,such as cetyl-trimethyl ammonium bromide(CTAB)and sodium dodecyl sulfonate(SDS),were added to alkaline electrolyte and the effects of the surfactants on the OER process were studied.The contact behavior of bubbles at the solid-liquid interface and the adhesion behavior of bubbles in the liquid phase were observed in situ.In the process of oxygen evolution,the size of the bubbles in the NiFe LDHs-CTAB system were much smaller and easy to escape from the surface of the electrodes,which maintained the intrinsic catalytic activity and stability of NiFe LDHs nanoarray electrodes.The introduction of cationic surfactant in electrolyte tailored the gas behavior on three-phase contact line,which could be applicable for design other excellent electrocatalysts used in gas evolution reaction.