Search

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]

The introduction of a surface ethylenediaminetetraacetate-metal coordination layer activates the Ni x Fe 3-x O 4 as an outstanding electrocatalyst for oxygen evolution reaction, exhibiting a very small overpotential of 180 mV at 10 mA cm−2 and excellent working durability. [Display omitted] Nickel-iron oxides are competitive electrocatalysts for oxygen evolution reaction, but their practical applications are restricted by the less-than-desirable intrinsic activity and working stability. To tackle the challenge, surface coordination chemistry is applied to the nickel–iron oxides through a complex-assisted in - situ crystal growth strategy. The ethylenediaminetetraacetate (EDTA) coordinated Ni x Fe 3-x O 4 (Ni x Fe 3-x O 4 -EDTA) is prepared by a simple one-pot hydrothermal process. The coordinated EDTA molecules can deeply alter the surface coordination structure of the Ni x Fe 3-x O 4. The Ni x Fe 3-x O 4 -EDTA demonstrates outstanding intrinsic activity towards oxygen evolution reaction, requiring only a small overpotential of 180 mV to reach 10 mA cm−2 in 1.0 M KOH. Moreover, the Ni x Fe 3-x O 4 -EDTA exhibits extremely stable long-term working stability. Density functional theory calculations show that the highly enhanced intrinsic activity is attributed to the surface coordinated EDTA-induced favorable electronic structure and coordination environment, which tunes the adsorption strength of the intermediates and optimizes the energetics of the elementary steps, while the high stability is ascribed to the strong coordination ability of EDTA. [ABSTRACT FROM AUTHOR]

Single atom catalysts (SAC) have the potential to achieve large-scale production of NH 3 through electrochemical nitrate reduction reaction (NO 3 -RR). Tailoring the coordination structure of the SAC can effectively tune their electronic structure and thus promote their catalytic selectivity and activity. In this work, Fe SAC with unique FeN 2 O 2 coordination was fabricated through direct pyrolysis of metal-organic frameworks that have pre-organized FeN 2 O 4 environment. Fe SAC exhibits both high faradaic efficiency (~92%) and high ammonia yield rate (46 mg h−1 mg cat. −1) in neutral electrolytes. Density functional theory calculations reveal that the O atoms in FeN 2 O 2 can tune the d -band center of Fe and thus adjust the adsorption energies of the NO 3 -RR intermediates. Compared to FeN 4 , FeN 2 O 2 structure has higher conductivity and selectivity to NH 3 and can spontaneously trigger the transformation of *NOH to N * , thus promoting the NO 3 -RR. This work provides a simple method to fabricate O, N-coordinated Fe SAC and may stimulate the flourishing development of asymmetric SAC for electrocatalysis. [Display omitted] ● A novel nut-like MOF was fabricated through the self-assembly of metal ions and ligands. ● Fe single atom catalyst with FeN 2 O 2 configuration can be obtained through the one-step pyrolysis of the as-prepared MOFs. ● Fe single atom catalysts exhibits a high faradaic efficiency of 92%, and a high NH 3 yield rate of 46 mg h−1 mg cat. -1. ● FeN 2 O 2 structure owns the enhanced conductivity and optimized rate-limiting steps compared with FeN 4 structure. [ABSTRACT FROM AUTHOR]