Structural Optimization And Electrocatalytic Performance Of Nickel Iron-based Layered Double Hydroxides

Hydrogen energy has become one of the most competitive green energy sources as a clean burning renewable energy.At present,electrocatalytic decomposition of water,including oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）,has attracted extensive attention as a promising method for hydrogen production.In order to overcome the electrochemical reaction barrier,both reactions need additional overpotential supply,so it is very important to develop electrocatalysts that reduce overpotential and promote the reaction to improve the efficiency of electrocatalytic water splitting for hydrogen production.At present,precious metal electrocatalysts such as ruthenium and iridium have high activity,but their scarcity and high cost limit their wide application.Hence,the design of low-cost and highly active non-noble metal catalysts for electrocatalytic decomposition of water to produce hydrogen has become a research focus.In this thesis,the high catalytic activity of nickel iron-based layered double hydroxides（NiFe LDH）was studied,and its electronic structure was optimized by using the strategies of interface engineering,third metal doping,and defect engineering,to improve its electrocatalytic activity.On this basis,the structure of the catalyst before and after the reaction was studied by in situ Raman spectroscopy,and the reaction mechanism of the catalyst was discussed.The specific research content mainly includes:（1）Construction of TeO₂@NiFe LDH heterojunction nanosheet and its application in hydrogen production by electrolysis of waterTeO₂ modified NiFe LDH nanosheets grown on nickel foam（NF）were prepared by combining hydrothermal method and electrodeposition method,and used for electrocatalytic water splitting for hydrogen production.Due to the strong interaction between TeO₂ and NiFe LDH,the TeO₂@NiFe LDH heterojunction is beneficial to the formation of Ni OOH active species and the exposure of more active sites,thus improving the electrocatalytic reaction activity.In 1.0 M KOH electrolyte,TeO₂@NiFe LDH requires overpotentials of 259.2 m V and234.3 m V overpotential to achieve 100 m A cm^-2 for OER and 10 m A cm^-2 for HER,respectively.TeO₂@NiFe LDH was assembled into electrolytic cell as anode and cathode in a fully water decomposition device with a low voltage of 1.62 V at a current density of 10 m A cm^-2.（2）Construction of Nb-doped NiFe LDH with superhydrophilic and superhydrophobic surfaces and its application in hydrogen production by electrolysis of water driven by solar cellsNb-doped NiFe LDH nanosheet arrays with OER and HER bifunctional electrocatalytic activity were prepared by one-step hydrothermal method and applied to the study of hydrogen production from water electrolysis driven by solar cells.By adjusting the amount of Nb doping,the influence of third metal doping on the electrocatalytic performance was studied.The prepared NiFe Nb LDH catalyst has a unique superhydrophilic/superhydrophobic surface and optimized electronic structure,resulting in high active site exposure,fast mass charge transfer,and good bubble escape ability.In addition,in-situ Raman spectra showed that Nb doping could optimize the electronic structure of NiFe LDH and further promote the surface reconstruction of LDH into Ni OOH active species with high OER activity.Based on the above structural advantages,NiFe Nb LDH needs 277 m V and 207 m V overpotential to achieve 100 m A cm^-2 OER and 10 m A cm^-2 HER current density in 1.0 M KOH electrolyte,respectively.Based on its good bifunctional electrocatalytic activity,NiFe Nb LDH was assembled into the electrolytic cell as anode and cathode,respectively.The hydrogen production system of the electrolytic cell can be driven by solar cell illumination,and the solar-hydrogen energy conversion efficiency（STH）of 15.56%can be achieved.（3）Construction of NiFe LDH/FeOOH heterojunction rich in oxygen vacancies for its application in hydrogen production by electrolysis of seawater driven by solar cellsOxygen-rich defective NiFe LDH/FeOOH nanosheets grown on nickel iron foam（INF）were prepared by a one-step electrodeposition method and used in the study of electrocatalytic decomposition of seawater to produce hydrogen driven by solar cells.The heterojunction formed by NiFe LDH and FeOOH forms a strong coupling interaction between the interface of the two phases,which can not only introduce oxygen vacancies to optimize the electronic structure of NiFe LDH,but also protect NiFe LDH against the corrosion of Cl^-in seawater,thus making the material have high catalytic activity and stability.In addition,in-situ Raman results show that NiFe LDH/FeOOH materials are more likely to form active Ni OOH intermediates during OER than NiFe LDH.In alkaline simulated seawater electrolyte,NiFe LDH/FeOOH requires overpotentials of 286.2 m V and 181.8 m V to achieve 100 m A cm^-2 for OER and 10 m A cm^-2 for HER,respectively.Based on its superior bifunctional activities,NiFe LDH/FeOOH was assembled into a simulated seawater electrolysis cell as both anode and cathode.The current density of the cell can reach 10 m A cm^-2 with a low overall water splitting voltage of 1.55 V,and there is almost no attenuation at a high current density of 100 m A cm^-2 for 105 h.The results show that it has good activity and stability of hydrogen production from seawater electrolysis.In addition,the system can be driven by solar cells,and the solar-hydrogen conversion efficiency（STH）of 15.64%can be achieved.