Self–supported NiFe LDH With Modulated Electronic Structure For Water Electrolysis

Hydrogen energy is widely considered as one of the most promising energy sources to replace fossil energy since the 21st century.Comparing to fossil energy conversion to hydrogen and biomass to hydrogen,whose high energy consumption and low conversion efficiency are disadvantages,water electrolysis to hydrogen is the most common and promising way to produce hydrogen.Yet,water electrolysis in alkaline conditions generally requires a voltage much larger than the theoretical voltage of 1.23 V and results in energy consumption.Therefore,an efficient and robust electrocatalyst for reducing the excess potential of the hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）at the cathode and anode respectively to reduce energy consumption is the focus of current research.Transition metal hydroxides are considered as one of the best alkaline electrolytic water catalyst choices due to their excellent OER performance,however,its poor electrical conductivity and their alkaline HER performance is inert and slow.Hence,it is far–reaching to investigate how to enhance the HER performance of transition metal–based hydroxides under alkaline conditions to make them competent for overall water splitting.In general,modulating the electronic structure to enhance the intrinsic catalytic activity,constructing heterogeneous interfaces to enlarge the number of active sites and coupling with conductive substrates to accelerate the mass and charge transfer rate to enhance the catalyst performance.Therefore,this thesis adopts in situ growth of catalysts on three–dimensional conductive substrates to enhance the electron transfer rate between the active sites of the catalysts.The electronic structure is tuned to optimize the adsorption energy of electrolytic water intermediates by constructing new active sites with different metal doping substitutions and the construction of heterogeneous interfaces.The specific research contents and conclusions of the paper are as follows.（1）Ultrathin NiFe Au LDH nanosheets with Au atoms replacing Fe centers have been formed via a facile and high–efficiency one–step coprecipitation method by adding a trace amount of HAu Cl₄ solution with conductive metallic nickel foam as a substrate and providing a nickel source for the reaction simultaneously.The content of Au elements plays an important role in the optimal HER and OER performance of NiFe Au LDH nanosheets.The experimental results indicate the strongly electronegative Au atoms change the electronic structure of NiFe LDH,large active specific surface area,accelerated mass and charge transfer process and optimized electronic structure provide a source of enhancement for the high electrolytic water performance for the material.The prepared NiFe Au LDH exhibits excellent HER performance:a low overpotential of only 89 m V is required at 10 m A cm^-2,and a low overpotential of only192 m V is required for driving at high current densities of 100 m A cm^-2.The OER performance is also greatly improved:the overpotentials of 181 m V and 267 m V could achieve current densities of 10 m A cm^-2 and 100 m A cm^-2,respectively.When using NiFe Au LDH as electrode for overall water reaction,a current density of 10 m A cm^-2 is obtained at a cell voltage of 1.57V.（2）The MoS₂ nanosheets are first hydrothermally synthesized on conductive substrate carbon cloth,and then MoS₂/NiFe LDH heterojunction catalysts are prepared by a fast and efficient electrodeposition method.Firstly,the MoS₂/NiFe LDH catalyst with the best active H adsorption energy is predicted by the theoretical guidance of DFT calculations,which provides a strong theoretical support for the experiments conducted.Secondly,the in situ coupling of MoS₂ and NiFe LDH is used to construct the heterostructure,accelerating the charge transfer rate and modulating the electronic structure to enhance the water splitting performance of the catalyst.The resulting MoS₂/NiFe LDH has excellent HER activity:a low overpotential of only98 m V is required to drive a current density of 10 m A cm^-2.And only the cell voltage of 1.61 V is required as a double electrode for the overall water splitting reaction and a long–term stability is maintained.