Preparation Of NiFe-based Catalysts And Their Electrocatalytic Water Splitting Performance

With the increasing problems of environmental pollution and energy crisis,more and more attention has been paid to the development and utilization of clean and renewable energy.During the development and utilization of new energy,solar energy,wind energy,tidal energy are difficult to connect this part of the electricity to the grid due to their own volatility,randomness and territoriality.Moreover,due to the constraints of the national grid security,the inter-regional transmission capacity is insufficient,resulting in the problem of excess capacity.Electrolyzed water technology can use this excess electrical energy to convert it into storable,high-calorie,clean and pollution-free hydrogen energy.However,water decomposition is a climbing process in thermodynamics,and requires external force to push it,such as electricity.At the same time,it will be accompanied by large energy consumption.In order to reduce energy consumption,it is necessary to develop a cost-effective water decomposition catalyst.NiFe-based catalysts have been widely studied due to their low price and excellent electrocatalytic performance.Among them,NiFe LDHs are easily synthesized,and the unique hydrotalcite-like structure has excellent oxygen evolution catalytic performance,but they also have the problems of poor conductivity and insufficient exposure of active sites,which is our main research oxygen evolution catalyst.In addition,the bond strength of OH-Ni(OH)2 is weak in alkaline environmenr,which has become the focus of our choice of hydrogen evolution catalysts.The main research of this paper is to expose the edge active sites of NiFe LDHs through heterogeneous construction to improve their oxygen evolution performance;using completely stripped NiFe LDHs as carriers and supporting IrO2 nanoparticles to synergistically catalyze the oxygen evolution reaction;using Ni(OH)2 nanotubes as carriers and loading Pt nanoparticles in order to improve the intrinsic activity of Pt and synergistically catalyze hydrogen evolution.The main research contents and conclusions are as follows:(1)Ni nanotube arrays(Ni NTAs)and 3D heterostructure NiFe LDH@Ni NTAs electrode materials with strong interfacial interaction were prepared,and the effect of the coupling of NiFe LDH and Ni NTAs on the oxygen evolution performance was studied.The results showed that NiFe LDH@Ni NTAs/NF exhibited a low overpotential of 191 mV at a current density of 10 mA cm-2 due to the reliable electron transfer from the intermediate metallic Ni NTAs to the external the NiFe LDH layer and more active sites that were exposed by highly dispersed ultrathin NiFe LDH nanosheets.(2)Bulk NiFe LDHs(bulk-NiFe LDHs)were synthesized and single layer NiFe LDHs(SL-NiFe LDHs)were obtained by layer-by-layer stripping.By adding an anchoring functional group as a coordination site,IrO2 supported SL-NiFe LDHs(IrO2@SL-NiFe LDHs)were prepared,and the agglomeration of IrO2 nanoparticles on NiFe LDHs was successfully suppressed to achieve effective binding of IrO2 and SL-NiFe LDHs.The structure and composition of IrO2@SL-NiFe LDHs were analyzed,and their oxygen evolution performance and mechanism were studied.The results showed that in the IrO2@SL-NiFe LDHs system,the edge Ir sites are more conducive to the formation of oxygen,while the oxygen sites on SL-NiFe LDHs are more conducive to the break of OH bonds.The combination of IrO2 and NiFe LDHs promotes OER;and the generation of oxygen vacancies on SL-NiFe LDHs further promotes the charge migration rate,reduces the OER energy barrier,and improves OER performance.Compared with SL-NiFe LDHs,the oxygen evolution overpotential at 10 mA cm-2 was reduced by 57 mV.(3)Ni(OH)2 nanotube arrays containing Ni(Ni-Ni(OH)2 NTAs)and Ni(OH)2 nanotube arrays(Ni(OH)2 NTAs)structures were prepared.Pt@Ni-Ni(OH)2 NTAs and Pt@Ni(OH)2 NTAs hydrogen evolution catalysts were prepared by electrodepositing Pt nanoparticles on nanotube arrays,and their structural composition analysis and hydrogen evolution performance tests were performed.The results showed that under basic conditions,the combination of Ni-Ni(OH)2 NTAs,Ni(OH)2 NTAs and the noble metal Pt was favorable for the hydrogen evolution reaction(HER);moreover,Ni(OH)2 NTAs containing metal Ni was more conducive to the deposition of Pt particles,thereby improving the inherent activity of Pt and promoting HER,and its hydrogen evolution overpotential at 10 mA cm-2 is 27 mV.