Revealing the surface structure-performance relationship of interface-engineered NiFe alloys for oxygen evolution reaction.

The bulk Ni/Fe ratio is a crucial parameter that determines the catalytic performance of the NiFe alloys by affecting the surface Fe/Ni ratio and the oxygen vacancy (O V) content, and the Ni 4 Fe 1 alloy with well-tailored oxide/metal interface presents highly enhanced oxygen evolution reaction with an overpotential of 242 mV at 10 mA cm−2 and a small Tafel slope of 37 mV dec−1. [Display omitted] NiFe alloys are among the most promising electrocatalysts for oxygen evolution reaction (OER). However, a comprehensive study is yet to be done to reveal the surface structure-performance relationship of NiFe alloys. In particular, the role of the ultrathin surface oxide layer, which is unavoidable for pure NiFe alloys, is always neglected. Herein, a series of NiFe alloys with different Ni/Fe ratios are fabricated. It is found that different Ni/Fe ratios lead to significant differences in surface composition and structure of the NiFe alloys, and thus affect their catalytic performance. Then, the oxide/metal interface of the Ni 4 Fe 1 alloy is tailored by adjusting the hydrogenation temperature to further understand the surface structure-activity relationship, and the optimal OER performance is achieved at the oxide/metal interfaces that have suitable surface Fe/Ni ratio and an appropriate amount of oxygen vacancies. In - situ Raman characterization shows that the Ni 4 Fe 1 alloy with well-tailored oxide/metal interface facilitates the formation of active species. Density functional theory calculations demonstrate that the ultrathin surface oxide layers are responsible for the high catalytic activity of the NiFe alloys, and that the quantity of oxygen vacancies in the surface oxides affects the adsorption energy of O* and thus to a great extent determines the catalytic activity. [ABSTRACT FROM AUTHOR]