| Constructing a green and renewable energy system is crucial for the stable development of human society.Hydrogen energy,generated from the renewable resource electrolysis of water,is considered to be one of the ideal energy sources of the future.The oxygen evolution reaction（OER）is a key step in water splitting,and limits the efficiency of hydrogen production from electrolytic water due to its high reaction energy barrier.NiFe-based materials are of great interest due to their abundance on earth and their excellent alkaline oxygen evolution properties.With the rapid development and application of in-situ characterization techniques,numerous studies have shown that electrode materials typically undergo in-situ structural evolution in catalytic reactions.Therefore,insight into the structural evolution of electrode materials in OER and accurate identification of the true active species in the reaction will help us to precisely tune the catalyst activity.In this thesis,NiFe-based oxygen precatalysts were studied and excellent oxygen evolution materials were obtained by constructing heterogeneous interfaces and introducing metallic elements Cr and non-metallic elements P.In-situ Raman、UV-vis spectra and other ex-situ techniques were used to investigate the structure evolution mechanism and the true active phase of the NiFebased materials.The main study work are as follows:（1）The FeOOH/NiFelayered double hydroxides（LDH）heterojunction catalysts were synthesized by a one-step etching method,and the surface structure evolution of FeOOH/NiFeLDH in the oxygen evolution reaction was investigated by in-situ UV-Vis and Raman spectroscopy.The results show that FeOOH/NiFeLDH evolves to the highly reactive FeOOH/β-Ni（Fe）OOH phase in the oxygen evolution reaction.the heterojunction of FeOOH/NiFeLDH promotes interfacial charge transfer,delays the oxidation of Ni2+to Ni3+/4+,and induces the NiFeLDH phase to the highly reactiveβ-Ni（Fe）OOH.FeOOH/β-Ni（Fe）OOH exhibited good oxygen evolution activity with an overpotential of100 is 252 m V and excellent long-term stability.（2）Here,the Ni3Cr@Fecomposite structure electrodes were prepared by a step-by-step electrodeposition method,successfully loading the Ni3Cr LDH outer layer with FeOOH.Combining in-situ Raman and UV-Vis spectroscopy with other ex-situ characterization results,we found that the existence of Cr in Ni3Cr LDH is conducive to the structural tr ansformation of the material to the highly reactiveβ-NiOOH and that the dissolution of Cr leads to the transformation ofβ-NiOOH toγ-NiOOH intermediates.For the Ni3Cr@Fecatalyst,the deposition of FeOOH on Ni3Cr LDH effectively solved the problem of massive Cr dissolution in alkaline solutions and inhibited the phase transition fromβ-NiOOH toγ-NiOOH.The synergistic catalytic interaction between the reconstitutedβ-Ni（Cr）OOH and FeOOH further enhanced the activity and long-term stability of the OER.The Ni3Cr@Feelectrode with a precipitation oxygen overpotential10 of 237 m V and a Tafel slope of 46.3 m V dec-1.（3）In the part of this thesis,the Ni5P4/FeP heterostructure was synthesized as OER precatalysts using FeOOH/NiFeLDH as precursors and P element were introduced by low temperature phosphorylation.The dynamic surface evolution of the Ni5P4/FeP precatalyst during electrochemical activation was researched by in-situ Raman and other ex-situ characterization.The study found that during electrochemical activation the Ni5P4/FeP surface was first derived as amorphous NiFe2O4 accompanied by large leaching of P elements.These intermediates show high OER activity and stability as the true active phase in the OER process.The electrochemical results show that the Ni5P4/FeP heterostructured electrode has a higher OER activity compared to the single-phase FeP and Ni5P4,with an overpotential of only 205 m V at a current density of 10 m Acm-2. |
