Monolayer Iron and Iron-Rich Hydroxide Nanosheets Exfoliated from High-Quality Green Rust for Enhanced Electrocatalytic Oxygen Evolution Reaction

Abstract

Ultrathin nanosheets of Ni-, Co-, and Fe-based (oxy)­hydroxides exhibit promising catalytic activity for the oxygen evolution reaction (OER) in water electrolysis under alkaline conditions. It has been revealed that Fe may play a crucial role in the catalytic process of Ni- or Co-based catalysts. However, it lacks effective methods to prepare and study pure Fe hydroxide nanosheets. In the present work, we report a topochemical synthesis of mixed-valent Fe2+–Fe3+ layered double hydroxides (LDHs), i.e., Green Rust (GR), featured with much higher quality and crystallinity compared to the traditionally synthesized ones. Monolayer Fe2+–Fe3+ LDH nanosheets with a thickness of ∼0.8 nm were derived from the GR product. In addition, a series of Ni-bearing Fe-rich LDH nanosheets were successfully prepared by the same method. The OER catalytic performance of the obtained Fe-rich LDH nanosheets achieved a small overpotential with η = 290 mV@10 mA cm–2 in 1 M KOH, which either outperforms or is comparable to the most active Ni–Fe LDH catalysts. The monolayer Fe2+–Fe3+ LDH nanosheets may be ideal for exploring the fundamental physicochemical properties of iron hydroxides from a molecular-scale perspective as well as serving as a building block for the assembly with other functional materials to obtain hybrid nanocatalysts.

A Novel Bubble‐based Microreactor for Enhanced Mass Transfer Dynamics toward Efficient Electrocatalytic Nitrogen Reduction

“…The eNRR performance achieved in this work is comparable to many of the reported results under ambient conditions in recent years (Table S8, Supporting Information). [3,[45][46][47][48] Thus, based on the above analysis, the mass transfer enhancement and HER inhibition effects could be fully demonstrated using the Ru/C and Fe/g-CN catalytic systems as well, indicating the excellent general applicability of the BBMR.…”

Porous and Partially Dehydrogenated Fe2+‐Containing Iron Oxyhydroxide Nanosheets for Efficient Electrochemical Nitrogen Reduction Reaction (ENRR)

“…Fe 2+ ‐Fe 3+ LDH nanosheets could be obtained via subsequent exfoliation of GR‐DS phase. [ 18 ] However, ferrous hydroxide in the Fe 2+ ‐rich LDH bulk and nanosheets is not stable in air atmosphere. To avoid unintended aerial oxidation or phase transformation during GR‐DS exfoliation, which deteriorates the quality and yield of the final nanosheets, further in situ oxidation to GR‐DS, that is, secondary oxidation, was conducted prior to the delamination.…”

“…Representative height profiles are illustrated in Figure 3b, corresponding to the thickness of the nanosheets marked by the same color lines in Figure 3a, which is slightly larger than the typical value of LDH nanosheets, that is, 0.8 ± 0.1 nm. [ 18,25 ] Zhou et al. reported that during the O 2 oxidation of dodecanoate intercalated GR (GR C12 ), Fe could dislocate from the initial sites with Fe polyhedrons linked above or below the host layer.…”

“…Representative height profiles are illustrated in Figure 3b, corresponding to the thickness of the nanosheets marked by the same color lines in Figure 3a, which is slightly larger than the typical value of LDH nanosheets, that is, 0.8 ± 0.1 nm. [18,25] Zhou et al reported that during the O 2 oxidation of dodecanoate intercalated GR (GR C12 ), Fe could dislocate from the initial sites with Fe polyhedrons linked above or below the host layer. Such a dislocation was evidenced by analyzing Fe local structures (e.g., Fe-O, Fe-Fe pairs) with high energy X-ray scattering and pair distribution function (PDF) analysis, also leading to some pores or defects in the layers and a larger intrinsic thickness.…”

Application of changing the valence state of metals through the reaction time for efficient oxygen evolution reaction

“…36,37 Different metal valence states can form different metal oxygen species, providing different reaction sites and intermediate binding sites. 38,39 Besides, carbon nanotubes (CNTs) can effectively accelerate electron transfer because they have the merits of a large specific surface area, low impedance, good chemical stability, and high conductivity. 40 The inclusion of CNTs in the preparation process is a common strategy to enhance a catalyst's conductivity and adjust the electronic structure of the catalyst.…”