Enhanced Electrochemical Lithium-Ion Charge Storage of Iron Oxide Nanosheets

Abstract

Iron oxides are appealing cathode materials for low-cost electrochemical energy storage, but iron oxide nanoparticles (NPs) exhibit very low capacities, particularly at fast charging and discharging times, which are increasingly important for numerous applications. We report that synthesis and stabilization of iron oxide in nanosheets results in significantly improved lithium-ion charge storage capacities compared to those of iron oxide NPs at both slow and fast charging/discharging times. The iron oxide nanosheets have lateral dimensions of ∼50 nm and thicknesses of ∼1 nm and are composed of smaller crystallites. The structure of the nanosheets is consistent with maghemite, γ-Fe 2 O 3 , which contains cation defects. The γ-Fe 2 O 3 phase is not typically observed within a nanosheet form, and γ-Fe 2 O 3 nanosheets transform to NPs at a relatively low temperature of 200 °C. The transformation of γ-Fe 2 O 3 from a nanosheet to an NP occurs in conjunction with removal of structural H 2 O. The γ-Fe 2 O 3 nanosheets exhibited lithium-ion charge storage capacities of up to 148 mA h g −1 , which is significantly greater than that of commercial γ-Fe 2 O 3 NPs (32 mA h g −1 ). γ-Fe 2 O 3 nanosheets showed the ability to be rapidly charged and discharged (93.2 mA h g −1 at a 9 min discharge time) with significantly higher capacities than γ-Fe 2 O 3 NPs. The electronic conductivity of the nanosheets was 3 times higher than that of NPs, which is attributed to facilitated electron conduction within the nanosheets. Kinetic analysis of the charge storage mechanism suggests the nanosheets store charge predominantly via a capacitive charge storage process rather than conventional intercalation. The understanding of how to synthesize and stabilize iron oxide nanosheets, their unique electrochemical properties, and their distinct charge storage mechanism furthers the design of charge storage materials with improved capacities, enhanced rate capabilities, and lower cost.

Strong Electronic Interaction of Amorphous Fe2O3 Nanosheets with Single‐Atom Pt toward Enhanced Carbon Monoxide Oxidation

“…The Pt/Fe 2 O 3 catalysts were prepared by a solvothermal method. The ethylene glycol (EG) is important for the formation of amorphous Fe 2 O 3 nanosheets . Unlike the layered materials, iron oxide phases, usually do not possess layered crystalline structures, henceforth, EG is needed to facilitate the formation of an amorphous Fe 2 O 3 nanosheet rather than a nanoparticle form .…”

“…Unlike the layered materials, iron oxide phases, usually do not possess layered crystalline structures, henceforth, EG is needed to facilitate the formation of an amorphous Fe 2 O 3 nanosheet rather than a nanoparticle form . The effect of EG on facilitating the formation of iron oxide nanosheets may be related to the complexation of EG with iron species during the dissociation and condensation reactions, as well as the suppress crystal growth along the other surfaces . By varying the amount of Pt loading and solvent, the dispersion and size of Pt metal were well controlled with their morphologies varying from isolated single atoms, loosely associated atoms clusters, sub‐nanoparticles to 3D large nanoparticles.…”

The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization, and Fundamentals

“…Also, the obvious intensity decrease of the B 1g (1) vibration band can be related to the decreased amount of vibrating Ti species due to increased Ti vacancy concentration. Niu et al [ 143 ] compared the Raman spectra of iron oxides prepared using ethylene glycol and H 2 O and treated at different temperatures, with the results shown in Figure 9b. The band structure of the as‐prepared nanosheets is similar to that of commercial γ‐Fe 2 O 3 , which is a naturally defective spinel phase.…”

“…Reproduced with permission. [ 143 ] Copyright 2017, American Chemical Society. c) FTIR spectra of pristine and Mo‐doped MnO 2 .…”

A Review on Iron Oxide‐Based Nanoarchitectures for Biomedical, Energy Storage, and Environmental Applications

“…One possible limitation is that MOF or PCP‐derived porous oxides tend to inherit the original shape of their precursors, although this may be addressed by introducing surfactants or other structuring agents during the preparation of the PCPs or MOFs. A summary of previously reported iron oxide nanostructures from 0D to 3D is given in Table 1 …”