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Iron oxides (FeOx), such as Fe2O3 and Fe3O4 materials, have attracted much attention because of their rich abundance, low cost, and environmental friendliness. However, FeOx, which is similar to most transition metal oxides, possesses a poor rate capability and cycling life. Thus, FeOx‐based materials consisting of FeOx, carbon, and metal‐based materials have been widely explored. This article mainly discusses FeOx‐based materials (Fe2O3 and Fe3O4) for electrochemical energy storage applications, including supercapacitors and rechargeable batteries (e.g., lithium‐ion batteries and sodium‐ion batteries). Furthermore, future perspectives and challenges of FeOx‐based materials for electrochemical energy storage are briefly discussed. FeOx‐based materials are potential anode materials in electrochemical energy storage. The comparison of various morphologies, synthetic methods, and electrochemical properties is presented. The applications of FeOx‐based materials for supercapacitors, lithium‐ion batteries, sodium‐ion batteries, lithium‐sodium‐ion batteries, and other rechargeable batteries are also comprehensively discussed.

Catalytic oxidation is widely recognized as a highly effective approach for eliminating highly toxic CO. The current challenge lies in designing catalysts that possess exceptional low-temperature activity and stability. In this work, we have prepared ultrafine platinum particles of ~1 nm diameter dispersed on a MgFe2O4 support and found that the addition of 3 wt.% FeOx into the 3Pt/MgFe2O4 significantly improves its activity and stability. At an ultra-low temperature of 30 °C, the CO can be totally converted to CO2 over 3FeOx-3Pt/MgFe2O4. High and stable performances of CO-catalytic oxidation can be obtained at 60 °C on 3FeOx-3Pt/MgFe2O4 over 35 min on-stream at WHSV = 30,000 mL/(g·h). Based on a series of characterizations including BET, XRD, ICP, STEM, H2-TPR, XPS, CO-DRIFT, O2-TPD and CO-TPD, it was disclosed that the relatively high activity and stability of 3FeOx-3Pt/MgFe2O4 is due to the fact that the addition of FeOx could facilitate the antioxidant capacity of Pt and oxygen mobility and increase the proportion of adsorbed oxygen species and the amounts of adsorbed CO. These results are helpful in designing Pt-based catalysts exhibiting higher activity and stability at low temperatures for the catalytic oxidation of CO.

Thermally synthesized graphitic carbon nitride (g-C3N4) over pulsed laser deposition (PLD) produced urchin-like iron oxide (FeOx) thin films were fabricated via in situ and ex situ processes. Materials characterisation revealed the formation of the graphitic allotrope of C3N4 and a bandgap Eg for the combined FeOx/g-C3N4 of 1.87 and 1.95 eV for each of the different fabrication strategies. The in situ method permitted to develop a novel petal-like morphology, whereas for the ex situ method, a morphological mixture between FeOx bulk and g-C3N4 was observed. Given the improved optical and morphological properties of the in situ film, it was employed as a proof of concept for the direct photocatalysis and photo-Fenton removal of ciprofloxacin antibiotic (CIP) under visible light irradiation. Improved photocatalytic activity (rate constant k = 8.28 × 10−4 min−1) was observed, with further enhancement under photo-Fenton conditions (k = 2.6 × 10−3 min−1), in comparison with FeOx + H2O2 (k = 1.6 × 10−3 min−1) and H2O2 only (k = 1.3 × 10−4 min−1). These effects demonstrate the in situ methodology as a viable route to obtain working heterojunctions for solar photocatalysis in thin-film materials, rather than the more common powder materials.

There are obvious drawbacks for the traditional treatment methods of antibiotics, such as low efficiency and high cost. In this paper, FeOx catalysts, modified with the biochar (BC) of maple leaf (FeOx@BC), were successfully prepared by the hydrothermal method. Then, the FeOx@BC was investigated to activate peroxymonosulfate (PMS) under UVA-LED irradiation for the degradation of tetracycline hydrochloride (TC). Subsequently, the changes in valence states before and after the reaction of ions were investigated by XPS spectra, and the process mechanism was presented. The results demonstrated that the TC degradation efficiency reached 96% in the FeOx@BC + PMS + UVA-LED system within 40 min, which was higher than 57% efficiency for the α-Fe2O3 + PMS + UVA-LED system. The electron transfer was promoted in the FeOx@BC + PMS + UVA-LED system due to the doping of BC. The Fe(III) was transformed into Fe(II) under UVA-LED irradiation, and Fe(II) activated continuously PMS to generate active oxygen species. Furthermore, it had excellent reusable performance and structural stability, and the degradation efficiency was still as high as 80% after five cycles. It was proved that SO4−•, •OH, O2•− and h+ participated in the degradation process of TC to different degrees by quenching experiments and EPR tests. In summary, FeOx@BC is an inexpensive, reusable and efficient catalyst.

The selective hydrogenolysis of 5-hydroxymethylfurfural (HMF) platform molecule to 2,5-dimethylfuran (DMF) has attracted increasing attention due to its broad range of applications. However, HMF, with multiple functional groups, produces various byproducts, hindering its use on an industrial scale. Herein, a bimetallic Pt-FeOx/AC catalyst with low Pt and FeOx loadings for selective HMF hydrogenolysis to DMF was prepared by incipient wetness impregnation. The structures and properties of different catalysts were characterized by XRD, XPS, TEM, ICP-OES and Py-FTIR techniques. The addition of FeOx enhanced Pt dispersion and the Lewis acidic site density of the catalysts, and was found to be able to inhibit C=C hydrogenation, thereby im-proving DMF yield. Moreover, the presence of Pt promoted the reduction of iron oxide, creating a strong interaction between Pt and FeOx. This synergistic effect originated from the activation of the C–O bond over FeOx species followed by hydrogenolysis over the adjacent Pt, and played a critical role in hydrogenolysis of HMF to DMF, achieving a yield of 91% under optimal reaction conditions. However, the leaching of Fe species caused a metal–acid imbalance, which led to an increase in ring hydrogenation products.

A significant challenge impeding the commercialization of fuel cell technology is the utilization of a high cost and poor stability of the noble platinum nanoparticles supported on carbon (Pt/C) as an oxygen reduction reaction (ORR) electrocatalyst at the cathode electrode. Herewith, we report the extremely durable and superior ORR electrocatalyst derived from Fe/FeO x encapsulated iron coordinated nitrogen doped carbon (FeNC) nanostructure by simply calcining the solid mixture containing oxidized carbon nanoparticle, melamine and iron (II) acetate at 700 (FeNC700), 800 (FeNC800) and 900 °C (FeNC900) under autogenic pressure condition. The maximum ORR performance with E onset and E 1/2 value of 1.04 and 0.89 V vs. RHE is achieved with the FeNC sample heated at 700 °C. The benchmark Pt/C electrocatalyst delivers E onset value of 1.04 V vs. RHE and E 1/2 value of 0.86 V vs. RHE. On the other hand, the FeNC catalyst promotes ORR process via a direct 4 electron transfer route accompanied by an extremely low number of intermediate substances. To understand the outstanding ORR performance of the synthesized catalysts, microstructure, phase, surface area and Fe-N x active site are investigated. It is found that the FeNC sample with larger content of Fe-N x active site coupled with the presence of Fe/FeO x encapsulated graphitic Fe-N x doped carbon structure results in the remarkably high ORR performance under alkaline media. Furthermore, the FeNC700 sample exhibits not only excellent resistance to methanol poisoning, but also negligible ORR degradation against the accelerated ORR durability test for 5,000 cycles.

The conversion of carbon dioxide into fuels and fine chemicals is a highly desirable route for mitigating flue gas emissions. However, achieving selectivity toward olefins remains challenging and typically requires high temperatures and pressures. Herein, we address this challenge using 12 nm copper nanoparticles supported on FeOx micro-rods, which promote the selective hydrogenation of CO2 to light olefins (C2–C4) under atmospheric pressure. This catalyst achieves up to 27% conversion and 52% selectivity toward C2–C4 olefins, along with the production of C2–C4 paraffins, C5+ hydrocarbons (with all C1+ products totalling to up to about 75%), and methane, while suppressing CO formation to just 1% at 340 °C. The enhanced performance of the Cu/FeOx pre-catalyst is attributed to the efficient in situ generation of iron carbides (Fe5C2) in the presence of copper nanoparticles, as confirmed by ex situ XRD analysis. Copper facilitates the reduction of FeOx to form Fe5C2, a crucial intermediate for shifting the reaction equilibrium toward higher hydrocarbons. The hydrogenation of CO2 to higher hydrocarbons proceeds through the reverse water–gas shift reaction coupled with Fischer–Tropsch synthesis.

The present study aims to explore a new method to improve the catalytic activity of non-precious metals, especially in electrochemical reactions. In this study, highly ionized Fe plasma produced by arc discharge uniformly deposit on porous carbon substrate and form atomic clusters by the Pulsed Arc Plasma Deposition technique. The as-prepared FeOx/C material was tested as a cathode material in rechargeable Li-O2 battery under different current rates. The results show a significantly improvement of the battery performance in both cycle life and reaction rate. Furthermore, XRD and SEM results show that the as-prepared cathode material has the ability to stabilize cathode and reduce side reactions, and current rate is a critical factor of the nucleation of the discharge products.

The chemical and magnetic states of Fe/Fe2O3 thin films prepared by e-beam evaporation were investigated by using element-specific techniques, X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). It was clearly shown that the Fe layers are oxidized to form an antiferromagnetic (AFM) FeOx<1, while the bottom oxide remained a weak ferromagnet (wFM) (α+γ)-type Fe2O3. Dependences of the peak intensities and lineshapes on the Fe thickness and measurement geometry further demonstrate that FeOx<1 layers reside mostly at the interface realizing an FM (Fe)/AFM (FeOx)/wFM (Fe2O3), whilst the spin directions lie in the sample plane for all the samples. The self-stabilized intermediate oxide can act as a physical barrier for spins to be injected into the wFM oxide, implying a substantial influence on tailoring the spin tunneling efficiency for spintronics application.

With TEMPO oxidation, it was possible to incorporate iron nanostructures into a cellulose nanofiber matrix. FTIR spectra showed the functional groups present in the films. The combination of both iron and CNF confers to the films good electrochemical activity; the electrochemical characterization (CV) showed that they present stability in the reduction process at a potential of 0–1 V, with the materials with 5% and 10% being the most active. The Pb reduction process shows that the 5% film is the material with the highest oxidizing capacity.