Structural Tuning Of NiFe Hydrotalcite-based Catalysts And Their Performance In Electrocatalytic Decomposition

Hydrogen is widely considered one of the most attractive energy sources due to its renewable and environmentally friendly properties.Among the various methods for generating hydrogen,electrochemical water splitting is a very promising approach.However,due to the slow kinetics of oxygen evolution reaction(OER),the efficiency of electrolyzed water is limited.Therefore,developing an electrocatalyst with high performance and low price is of great significance to the overall electrolysis of water.Two-dimensional layered double hydroxide(LDH)is considered to be one of the most advanced catalysts for OER in terms of structural composition,synthesis technology,physicochemical properties and catalytic activity.However,the low electrical conductivity and the small number of active sites of bulk LDH affect its performance in OER.In this work,in order to solve these problems in OER,we have improved the structure and conductivity of LDH.The specific research content is as follows:(1)Amorphous NiFe-layered double hydroxides nanosheets for oxygen evolution reaction.The exposed active sites of NiFe layered double hydroxide(NiFe-LDH)for oxygen evolution reaction(OER)are limited by the compact packing of its two-dimensional lamella.In this work,amorphous NiFe-LDH(A-NiFe-LDH)with abundant active sites are synthesized by using Ni(II)nitrilotriacetate complex anion([NTANi]-)as a morphological control agent,which can expose more active sites of NiFe-LDH by controlling crystalline phase and grain size of NiFe-LDH.Structural characterization demonstrates that[NTANi]-is adsorbed on the surface of A-NiFe-LDH and confirm A-NiFe-LDH is amorphous.The electrocatalytic activity of A-NiFe-LDH for OER is much higher than that of both RuO2 and pristine NiFe-LDH.A-NiFe-LDH has a low OER overpotential of 241 mV at 10 mA cm-2 and a small Tafel slope of 55 mV dec-1.The high electrocatalytic activity of A-NiFe-LDH could be attributed to its amorphous structure.(2)Design and construct NiFeCr-LDH/NiS/NF multilayer nano-arrays for efficient oxygen evolution reactions.By constructing a NiS/NF array as a conductive substrate,using the characteristics of the high conductivity of the NiS array and the fine structure to facilitate gas transportation,a simple solvothermal method was used to load NiFeCr-LDHs on the NiS/NF array.Its unique multilayer structure has made important contributions to excellent performance.The overpotential of the NiFeCr-LDHs/NiS/NF electrode at a current density of 10 mAcm-2 is only 193 mV at 1.0 M KOH,and its Tafel slope is 52 mV dec-1.At the same time,XPS characterization has shown that the significant improvement in OER performance is also inseparable from the interaction between NiFeCr-LDHs and NiS.This work proposes a novel and simple design and construction of multi-layer supported catalysts,which has reference value for future material structure design.(3)The NiFeCr-S/NiS/NF modified 2D nanosheet array is used as an effective dual-function electrocatalyst for the total hydrolysis of water.In this chapter,the template method is used.The NiFeCr-LDHs/NiS/NF electrode synthesized in the previous chapter is used as a morphology guide and metal precursor.NiFeCr-S/NiS/NF electrode is synthesized by vapor deposition.NiFeCr-S/NiS/NF successfully retained the multi-layered array structure of the NiFeCr-LDHs/NiS/NF.As a dual-functional catalyst,NiFeCr-S/NiS/NF materials have excellent oxygen evolution reaction and hydrogen evolution reaction performance.The overpotentials of OER and HER at 10 mAcm-2 are 93 mV and 119 mV,respectively.At the same time,it has excellent long-term stability in a solution of 1.0 M KOH+0.2 M Na2S.The significant improvement of OER and HER performance is closely related to the formation of the NiFeCr-S.At the same time,compared with the NiFeCr-S/NF,the excellent performance of the NiFeCr-S/NiS/NF electrode is also inseparable from the modified multi-layer nanosheets and the interaction of NiFeCr-S and NiS.In the overall water electrolysis,the NiFeCr-S/NiS/NF//NiFeCr-S/NiS/NF system shows satisfactory performance.At a current density of 10 mA cm-2,the overpotential is 300 mV.This work provides a new idea for the preparation of new fine-structured TMS materials.