Phase-Induced Shape Evolution of FeNi Nanoalloys and Their Air Stability by in-Situ Surface Passivation

Abstract

Shape and size of nanoparticles are fundamental structural properties that govern the development of novel surface-related applications. Traditionally external agents such as surfactants, reducing agents, or stabilizers have been used for enforcing preferential growth orientation, size, and shape to develop tailor-made nanoparticles. However, these external agents cover the pristine surface of the particle and invariably reduce the surface activity. Here, we introduce a surfactant-free, single-step electrochemical method to control the shape of air-stable FeNi alloy nanoparticles. Using glancing-incidence X-ray diffraction, we further demonstrate that the shape evolution of nanoparticles from concave cube to truncated sphere occurs concurrently with the phase transformation from bcc to fcc. This shape evolution can be achieved by fine-tuning a single parameter, the ratio of reactant concentrations (i.e., [Ni2+]/[Fe2+]). Addition of Ni2+ to the Fe2+ electrolyte changes the nucleation mechanism from progressive growth for pure Fe2+ electrolyte to instantaneous growth for mixed Fe2+/Ni2+ electrolyte, which leads to a remarkably narrow size distribution and very uniform dispersion on the Si substrate. Depth-profiling X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis by both transmission electron microscopy and scanning electron microscopy for nanoparticles at different growth stages reveal alloy formation and preferential deposition of Fe during initial growth that results in a quasi-core–shell structure. We also observe the in-situ formation of a very thin Ni-doped FeOOH outer layer and NiFe2O4 intermediate layer on the skin of the nanoparticles, which passivates the surface and dramatically enhances the air stability. The present work provides a unique example of shape-controlled bimetallic nanostructures and offers insights into growth modification of a host metal structure by a guest metal.

Active sites for tandem reactions of CO 2 reduction and ethane dehydrogenation

“…This confirmed that the interaction between Fe and Ni resulted in a structural variation of active sites, leading to significant differences in the reaction mechanism and product selectivity. was calculated to be 3.575 and 3.570 Å, respectively, which is slightly larger than that of metallic Ni, indicating the formation of Ni-rich NiFe alloy with fcc structure (22). This conclusion was verified by the corresponding peak shift for both catalysts under various treatment conditions ( Fig.…”

FeNi nanoparticles on Mo2TiC2Tx MXene@nickel foam as robust electrocatalysts for overall water splitting

“…The peaks at 855.7 and 861.5 eV are from surface oxidized Ni 2+ [35,36]. Further analysis reveals a positive binding energy shift for Ni 2p3/2 in comparison with reported FeNi system [38,39]. Figure 3(d) shows the metallic Fe with binding energy at 706.8 eV, and the fitted signals at 707.9, 710, 711.3, 712.5, and 713.5 eV are surface oxidized Fe 2+ [35,40].…”

“…Figure 3(d) shows the metallic Fe with binding energy at 706.8 eV, and the fitted signals at 707.9, 710, 711.3, 712.5, and 713.5 eV are surface oxidized Fe 2+ [35,40]. Moreover, a slight positive shift is on Fe 2p3/2 compared to pure FeNi system [38,39]. Therefore, the variation of electronic structure results in the interfacial interaction between FeNi NPs and Mo2TiC2Tx, which can effectively affect the electrocatalytic activity.…”

Core/Shell NiFe Nanoalloy with a Discrete N‐doped Graphitic Carbon Cover for Enhanced Water Oxidation

“…The doublets at 853.1 eV/870.7 eV and 707.3 eV/720.8 eV are ascribed to Ni 0 and Fe 0 accordingly, representing the metallic Ni and Fe in the alloy. The peaks located at 854.9 eV, 856.7 eV and 711.7 eV are assigned to Ni 2+ , Ni 3+ and Fe 3+ , respectively, all of which result from the in‐situ oxides formed at the exposed alloy surfaces . As the XRD and Raman analyses did not depict crystalline oxide phases, it is possible that these surface oxides are either clusters or amorphous in nature.…”