Experimental And Theoretical Study On Oxygen Evolution Reaction Of Defect And Metal Doped NiFe LDH

Oxygen evolution reaction(OER)has important application value in the field of water oxidation industry and rechargeable metal-air battery.Nickel-iron layered double hydroxides(NiFe LDHs)have been extensively studied as an excellent OER catalyst in alkaline system.How to further improve the intrinsic catalytic performance of NiFe LDH as well as theoretically revealing the catalytic mechanism of NiFe LDH material has rarely been reported.In this thesis,a simple and high-efficiency oxygen-defective NiFe LDH(Ov-NiFe LDH)preparation method was firstly developed.The slightly NaBH4 reduction method was used to control the introduction of oxygen vacancies into NiFe LDH and the nanoarray architecture was well maintained.The catalytic achieved an overpotential of 200 mV at the current density of 10 mA/cm2.Density Functional Theory(DFT)was employed to further understand the catalytic mechanism of Ov-NiFe LDH,it was found that the presence of oxygen defects can increase the electron density distribution of the Ni-Fe bridge active center and regulate the valence state of the active center.The potential-determining step of the process was also greatly reduced.Combined with experimental evidences,in order to further explore the catalytic performance mechanism of oxygen vacancy in NiFe LDH,we constructed the Ov-NiFe LDH structure model.Comparing the Ni sites,Fe site and the traditional Fe site with the existence of oxygen vacancies in OER process,it was found that the adsorption of OH groups on active sites showed different reaction kinetics.Electron density distribution and partial density of states analysis revealed that electrocatalytic performance of Ov-NiFe LDH was optimized by reduced oxidation state of the active site,shorted band gap width,faster the electron transport capacity,and appropriatly regulated adsorption OH group.Transition metal doping strategy has been widely used to improve the catalytic performance of NiFe LDH,but its mechanism for promoting OER process lacks deeply theoretical analysis.The Fe2+/Mn2+doped NiFe LDH models were constructed.Based on electron density distribution and local(energy)density analysis,it is found that Fe2+-O-Fe structure can promote oxidation of Fe to high valence of Fe4+ and stabilizing the reaction intermediate state of Fe4+.Moreover,as for the Mn 2+doping,the Mn2+-O-Fe structure boosted the d energy band center of the Fe site to be closer to the Fermi level,resulting in an increase in conductivity.At this time,the anti-bonding orbital of the active site shifted upwards and remained semi-full state,showing suitable OH group coordination ability.Thereby,the overpotential of the rate-limiting step was reduced and accelerating the entire catalytic performance was enhanced.Based on experimental facts and theoretical calculations,the mechanism of oxygen vacancy and transition metal ion doping strategy to improve the catalytic performance of NiFe LDH material OER is revealed in this paper.It will provide a new horizon for exploring OER catalysts with better performance and higher efficience.