Understanding The Surface/Interface Structure-Performance Relationship On Ni Fe Electrocatalysts For Water Oxidation

Developing high reactive and stable water oxidation electrocatalysts is the key to the application of clean energy.Understanding the mechanism of the oxygen evolution reaction(OER)at the catalysts-electrolytes interfaces can efficiently guide the rational design of the catalysts.Identifying the evolution of the surface/interface structure at the OER process can provide useful clues on the mechanism investigation.However,limited by the high dynamic evolution of the surface/interface structure during OER and the interference of the structure from the bulk,it remains a great challenge to do operando investigation on identifying the active structure of the surface/interface.In this thesis,we select the NiFe based OER cata-lysts,which is the most promising electrocatalysts towards real-life applications in the alkali environments,as the platform.Benefiting from the advanced operando synchrotron X-ray characterization,we have done the following research:1,In chapter 3,we investigated the surface electronic and chemical structures of a NiFe based hydroxide with 100%exposure of the active sites at the OER state and found that the formation of tetravalent Niand Fe is prerequisite for the initiation of OER.The possible OER mechanism has also been revealed.2,In chapter 4,we investigated the evolution of surface chemical elements distribution of a NiFe based hydroxide at OER state.We found that the degradation of OER performance of this kind of catalyst is attributed to the segregation of Fe.Meanwhile,we found that the Fe segregation can be reversed at low potential.Benefiting from this reversible Fe segrega-tion,we successfully revive the degraded catalysts.3,In chapter 5,we investigated the Fe incorporation mechanism of 2D Ni(OH)₂ nano-sheets.We found that Fe is preferably deposited at the edge sites of the Ni(OH)₂ nanosheets.The enhanced reducibility of Niby the addition of Fe at its adjacent site was the reason for the enhancement of OER performance.4,In chapter 6,we investigate the influence of interfacial stress at NiOOH/NiO inter-faces on the OER performance and stability.We found that compressive stress in the NiOOH is beneficial to the enhancement of its OER performance.Through these studies,we build a bridge between the evolution of the surface/interface structure and the OER reactivity and provide mechanism understanding to guide the mate-rial design.