Fe Doping Research Articles

Fe doping regulates the surface reconstruction and activates lattice oxygen of NiCr LDH for water oxidation

Deep profiling of the structural evolution during dynamic surface reconstruction of lattice oxygen mechanism (LOM)-based metal double hydroxide catalysts is challenging. Herein, we propose that the doping of Fe in nickel chromium layered double hydroxide (Fex-NiCr LDH) can optimize the surface reconstruction behavior in the oxygen evolution reaction (OER) by modulating Cr leaching. Operando Raman results indicate that the Fe0.5-NiCr LDH is dynamically reconstructed into metal oxyhydroxide as the active center, and Fe doping reduces the oxidation potential of Ni2+. Density functional theory (DFT) results reveal that Fe doping shifts the O 2p band upward and increases the covalency of the metal–oxygen bond, thereby promoting lattice oxygen oxidation. The optimal Act100-Fe0.5-NiCr LDH exhibits a low overpotential of 208.4 mV at 100 mA cm−2. Moreover, Act100-Fe0.5-NiCr LDH displays low voltage and high stability (1.47 V and 100 h at 10 mA cm−2) for overall water splitting. This work offers an important basis for understanding the reconstruction mechanism of LOM-based catalysts and provides new insights for identifying the activity origins.

Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation

Oxygen evolution reaction (OER) is critical to renewable energy conversion technologies, but the structure-activity relationships and underlying catalytic mechanisms in catalysts are not fully understood. We herein demonstrate a strategy to promote OER with simultaneously achieved lattice oxygen activation and enhanced local electric field by dual doping of cations and anions. Rough arrays of Fe and F co-doped CoO nanoneedles are constructed, and a low overpotential of 277 mV at 500 mA cm−2 is achieved. The dually doped Fe and F could cooperatively tailor the electronic properties of CoO, leading to improved metal-oxygen covalency and stimulated lattice oxygen activation. Particularly, Fe doping induces a synergetic effect of tip enhancement and proximity effect, which effectively concentrates OH− ions, optimizes reaction energy barrier and promotes O2 desorption. This work demonstrates a conceptual strategy to couple lattice oxygen and local electric field for effective electrocatalytic water oxidation.

Effects of Magnetic Fe Doping on the Thermoelectric Properties of TiNiSn Nanomaterials prepared via melt spinning method

As a kind of high temperature thermoelectric material, TiNiSn compound has the characteristics of high power factor and high thermal conductivity. Its thermoelectric performance is largely limited by the high thermal conductivity. In this paper, TiNiFexSn(x=0-0.05) samples are prepared by melt spinning combined with spark plasma sintering method. The results show that there are nanocrystals existed in the samples with a size of around 200nm. The grain size of the samples is refined through the melt-spinning process, and the lattice thermal conductivity is lower compared with the arc-melted samples. With the increase of Fe content, the lattice thermal conductivity of TiNiFexSn samples decreases, reaching a minimum value of 3.31W/mK when x=0.02, which is 44% lower than that of TiNiSn matrix. The carrier concentration of TiNiFexSn samples increases due to the doping of Fe, resulting in an increase of electrical conductivity and decrease of Seebeck coefficient and finally improvement of the power factor. The maximum zT value of TiNiFe0.03Sn sample is 0.54 at 900K, which is 35% higher than that of TiNiSn samples. This work shows that the melt spinning and magnetic Fe doping can effectively improve the thermoelectric properties of TiNiSn.

Fe doping mechanism of Na0.44MnO2 tunnel phase cathode electrode in sodium-ion batteries

Due to its stability and low cost, the tunnel-style sodium-manganese oxide (Na0.44MnO2) material is deemed a popular cathode choice for sodium-ion rechargeable batteries. However, the Jahn-Teller effect caused by Mn3+ in the material results in poor capacity and cycling stability. The purpose of this experimental study is to partially replace Mn3+ with Fe3+, in order to reduce the Jahn-Teller effect of the material during charging and discharging process. The results of Raman spectroscopy and X-ray photoelectron spectroscopy confirmed that the content of Mn3+ decreased after Fe3+ doping. Electrochemical studies show that the Na0.44Mn0.994Fe0.006O2 cathode has better rate performance (exhibits a reversible capacity of 87.9 mAh/g at 2 C) and cycle stability in sodium-ion batteries. The diffusion coefficient of sodium ions increases by Fe3+ doping. The excellent rate performance and capacity improvement are verified by density functional theory (DFT) calculation. After doping, the band gap decreases significantly, and the results show that the state density of O 2p increases near the Fermi level, which promotes the oxidation–reduction of oxygen. This work provides a straightforward approach to enhance the performance of Na0.44MnO2 nanorods, and this performance improvement has guiding significance for the design of other materials in the energy storage domain.

Investigating the Influence of Impurity Defects on the Adsorption Behavior of Hydrated Sc3+ on the Kaolinite (001) Surface Using Density Functional Theory.

In natural kaolinite lattices, Al3+ can potentially be substituted by cations such as Mg2+, Ca2+, and Fe3+, thereby influencing its adsorption characteristics towards rare earth elements like Sc3+. Density functional theory (DFT) has emerged as a crucial tool in the study of adsorption phenomena, particularly for understanding the complex interactions of rare earth elements with clay minerals. This study employed DFT to investigate the impact of these three dopant elements on the adsorption of hydrated Sc3+ on the kaolinite (001) Al-OH surface. We discerned that the optimal adsorption configuration for hydrated Sc3+ is Sc(H2O)83+, with a preference for adsorption at the deprotonated Ou sites. Among the dopants, Mg doping exhibited superior stability with a binding energy of -4.311 eV and the most negative adsorption energy of -1104.16 kJ/mol. Both Mg and Ca doping enhanced the covalency of the Al-O bond, leading to a subtle shift in the overall density of states towards higher energies, thereby augmenting the reactivity of the O atoms. In contrast, Fe doping caused a pronounced shift in the density of states towards lower energies. Compared to the undoped kaolinite, Mg and Ca doping further diminished the adsorption energy of hydrated Sc3+ and increased its coordination number, while Fe doping elevated the adsorption energy. This study offers profound insights into understanding the role of dopant elements in the adsorption of hydrated Sc3+ on kaolinite.

Bifunctional Substrates: In‐situ Ni, Fe co‐doped Cobalt Carbonate Hydroxides for Overall Water Splitting

AbstractDeveloping highly efficient and stable electrocatalysts with large current densities for hydrogen and oxygen evolution is still challenging. Herein, Ni and Fe co‐doped cobalt carbonate hydroxide catalysts were designed in situ on the three‐dimensional porous NiFe foam through a facile one‐step hydrothermal strategy. Inductively coupled plasma atomic emission spectrum, transmission electron microscopy‐element mapping, X‐ray photoelectron spectroscopy, and DFT calculations demonstrate that the three‐dimensional NiFe foam substrate not only serves as the porous substrate, which enhances the exposed number of active sites, but also enhances the intrinsic activities of single active sites via introducing Ni and Fe dopants in the cobalt carbonate hydroxide catalyst during the hydrothermal process. The obtained hybrid electrocatalyst can be employed as a highly efficient and stable bifunctional electrocatalyst for the oxygen and hydrogen evolution reactions, with overpotentials of 340 mV and 371 mV at 1000 mA cm−2, respectively. In addition, tests in an alkaline electrolyzer revealed that the current density could reach 1000 mA cm−2 at a voltage of 2 V and maintain stable operation for 100 h.

P-bridged Fe-X-Co coupled sites in hollow carbon spheres for efficient hydrogen generation

Non-precious metals have shown attractive catalytic prospects in hydrogen production from ammonia borane hydrolysis. However, the sluggish reaction kinetics in the hydrolysis process remains a challenge. Herein, P-bridged Fe-X-Co coupled sites in hollow carbon spheres (Fe-CoP@C) has been synthesized through in situ template solvothermal and subsequent surface-phosphorization. Benefiting from the optimized electronic structure induced by Fe doping to enhance the specific activity of Co sites, bimetallic synergy and hollow structure, the as-prepared Fe-CoP@C exhibits superior performances with a turnover frequency (TOF) of 183.5 min−1, and stability of over 5 cycles for ammonia borane hydrolysis, comparable to noble metal catalysts. Theoretical calculations reveal that the P-bridged Fe-X-Co coupled sites on the Fe-CoP@C catalyst surfaces is beneficial to adsorb reactant molecules and reduce their reaction barrier. This strategy of constructing hollow P-bridged bimetallic coupled sites may open new avenues for non-precious metal catalysis.

Lattice oxygen-mediated Co–O–Fe formation in Co-MOF via Fe doping and ligand design for efficient oxygen evolution

The rational design of metal-organic frameworks (MOFs) provides potential opportunities for improving energy conversion efficiency. However, developing efficient MOF-based electrocatalysts remains highly challenging. Herein, a strategy involving strain engineering is developed to promote the electrocatalytic performance of MOFs by optimizing electronic configuration and improving the active site. As expected, the optimized CoFe–BDCNO2 exhibits a low overpotential of 292 mV at 10 mA cm–2 and a small Tafel slope of 31.6 mV dec–1 as oxygen evolution reaction (OER) electrocatalyst. Notably, when CoFe–BDCNO2 is prepared on Nickel foam (NF), the overpotential is only 345 mV at 1 A cm–2, which ensures efficient water oxidation properties. Integrating CoFe–BDCNO2/NF anode in membrane electrode assembly (MEA) for overall water splitting and CO2 reduction reaction (CO2RR) tests, the results show that the cell voltages of CoFe–BDCNO2/NF are 3.14 and 3.09 V at 300 mA cm–2 (25 °C), respectively, indicating that MOFs have various practical application prospects. The research of the structure-performance relationship reveals the lattice oxygen oxidation mechanism (LOM) where the Co-O-Fe bond is formed during the OER process by changing the electronic environment and coordination structure of CoFe–BDCNO2, and with high valence Co as active center, which provides a deep understanding of the structure design of MOFs and their structural transformation during OER.

Fe-Doped SDC Solid Solution as an Electrolyte for Low-to-Intermediate-Temperature Solid Oxide Fuel Cells.

Ceria-based oxides, such as samaria-doped ceria (SDC), are potential electrolytes for low-to-intermediate-temperature solid oxide fuel cells (SOFCs). The sinterability of these materials can be improved by adding iron as the sintering aid. This work reveals that Fe is soluble in SDC, forming an Fe-doped SDC solid solution. It is found that the solubility is affected by the sintering temperature. Fe doping has obvious effects on electrolyte properties, including sintering characteristics, thermal expansion behaviors, and electrical conductivities in both air and hydrogen atmospheres. The conductivity obviously increases while the activation energy decreases by doping Fe. Compared with that of the bare SDC electrolyte, the performance of the single cell with the Fe-doped SDC is enhanced; for example, the peak power density is increased by 52.8% to 0.726 W cm-2 at 600 °C when humidified hydrogen is used as the fuel and ambient air is used as the oxidant. The single cell showed stable operation at 600 °C under a constant current density of 0.3 A cm-2 for 150 h. Therefore, the Fe-doped SDC solid solution shows promise as a potential electrolyte for low-to-intermediate-temperature SOFCs.

Laser assisted oxygen vacancy engineering on Fe doped CoO nanoparticles for oxygen evolution at large current density

Exploring cost-effective non-noble metal-based catalysts with high activity and stability is of great significance for energy conversion and storage involving oxygen evolution reaction (OER). Here, we employed a laser irradiation technique to synthesis Fe doped CoO nanoparticles with ultrafine size (≈ 5.4 nm) and abundant oxygen vacancies (Fe-Ov-CoO). The ultrafine size of Fe-Ov-CoO nanoparticles provides more active sites to be exposed. Fe doping and oxygen vacancy promote the intrinsic activity and electron transfer rates of Fe-Ov-CoO, giving rise to high activity and stability catalyst for OER. Fe-Ov-CoO delivers a large current density of 1000 mA cm−2 at an overpotential of 548 mV, which is much better than commercial RuO2. Moreover, Fe-Ov-CoO presents a remarkable long-term stability with negligible degeneration at a high current density of 500 mA cm−2 for 120 h. This work provides a new route to develop OER electrocatalyst with high activity and stability.

Accessible Ni‐Fe‐Oxalate Framework for Electrochemical Urea Oxidation with Radically Enhanced Kinetics

AbstractUrea oxidation reaction (UOR) has been utilized to substitute the oxygen evolution reaction (OER), to escalate the energy conversion efficiency in electrochemical hydrogen generation processes with denitrification of widespread urea in wastewater. This study reports breakthroughs in Ni‐based UOR electrocatalysts, particularly with NiFe oxalate (O‐NFF), derived from Ni3Fe alloy foam with prismatic nanostructures and elevated surface area. The O‐NFF achieves cutting‐edge performances, representing 500 mA cm−2 of current density at 1.47 V RHE and exceptionally low Tafel slope of 12.1 mV dec−1 (in 1 m KOH with 0.33 m urea). X‐ray photoelectron/absorption spectroscopy (XPS/XAS) coupled with density functional theory calculations unveil that oxalate ligands induce charge deficient Ni center, promoting stable urea‐O adsorption. Furthermore, Fe dopants enhance oxalate‐O charge density and H‐bond strength, facilitating C‐N cleavage for N2 and NO2− formation. The extraordinary UOR kinetics by the tandem effects of oxalate and Fe prevent Ni over‐oxidation, corroborated by operando XAS, minimizing OER interference. It agrees with an adaptive reconstruction to Fe‐doped β‐NiOOH on top surface in extended urea electrolysis with marginal loss in UOR kinetics. This findings shed light to bimetal‐organic‐framework as (pre)catalysts to improve industrial electrolytic H2 production.

Discovery of Deactivation Phenomenon in NiCo2S4/NiS2 Electromagnetic Wave Absorbent and Its Reactivation Mechanism.

Over the past century, extensive research has been carried out on various types of microwave absorption (MA) materials, primarily emphasizing mechanism, performance, and even toward smart device. However, the deactivation, a crucial concern for practical applications, has long been long-neglected. In this work, an in-depth exploration of the deactivation mechanism reveals a significant competition between metal and oxygen, leading to the replacement of the S-M (M = Ni and Co) bond by a new S─O bond on the surface of absorber. This substitution initiates a series of collapse effect that introduces additional defective sites and diminishes the potential for charge transport. Subsequently, passive and active anti-deactivation strategies are developed to target the deactivation. The passive strategy involved intentionally creating electron-deficient structures at the initial Ni and Co sites in the crystal through the Fe doping engineering, with the objective of preventing the generation of S─O bonds. Furthermore, the active anti-deactivation strategy allows for the precise control of absorber deactivation and reactivation by employing accelerated thermodynamic and kinetic methods, enabling a reversible transformation of S-M through competitive reactions with S─O bonds. Finally, a fast deactivation and reactivation method is first proposed promising to stimulate further innovations and breakthroughs in practical applications.

Synergistic effect of Fe doping and oxygen vacancy in AgIO3 for effectively degrading organic pollutants under natural sunlight

In this work, a series of hydrogenated Fe-doped AgIO3 (FAI-x) catalysts are synthesized for photodegrading diverse azo dyes and antibiotics. Under the irradiation of natural sunlight with a light intensity of ∼60 mW/cm2, the optimum FAI-10 exhibits a considerable rate constant for decomposing methyl orange (MO) of 0.067 min−1, about 7.4 times higher than that of AgIO3 (0.009 min−1), and 24.6% and 83.8% of MO can be decomposed over AgIO3 and FAI-10 after irradiation for 40 min. In the amplification photodegradation experiments with using 0.5 g catalyst and 400 mL MO dye solution (10 mg/L), FAI-10 possesses greatly higher photoreactivity to common semiconductors (ZnO, TiO2, In2O3 and Bi2MoO6), and the photodegradation rates over FAI-10 are 92%. Particularly, the FAI-10 shows superior stability, the activity of which remains unaltered after 8 continuous cycles. Foreign ions and water bodies have slight effect on the activity of FAI-10, but the MO degradation rates are decreased by adjusting pH values, especially when pH = 11 because of the strong electrostatic repulsion between MO and FAI-10. FAI-10 can also effectively decompose another azo dye (rhodamine B (RhB)) and diverse antibiotics (sulflsoxazole (SOX), chlortetracycline hydrochloride (CTC), tetracycline hydrochloride (TC) and ofloxacin (OFX)). The activity enhancement mechanism of FAI-10 has been systemically investigated and is ascribed to the promoted photo-absorption, charge separation and transfer efficiency, and affinity of organic pollutants, owing to the synergistic effect of Fe doping and oxygen vacancy (Ov). The photocatalytic mechanisms and process for decomposing MO are verified and proposed based on radical trapping experiments and liquid chromatography-mass spectrometry (LC-MS). This work opens an avenue for the fabrication of effective photocatalysts toward water purification.

Study on the Effect of Fe Doping on SCR Activity and Reaction Mechanism of Mn–TiO2 Catalysts

Study on the Effect of Fe Doping on SCR Activity and Reaction Mechanism of Mn–TiO2 Catalysts

A novel preparation of trace iron-doped 3D urchin-like TiO2 for efficient degradation and mineralization of trimethoprim under simulated sunlight

In this study, trace iron-doped 3D urchin-like titanium dioxide (Fe–TiO2) were prepared via a straightforward water bath process. The successful incorporation of trace iron into the TiO2 structure was confirmed through detailed EDX, EPR, and XPS analyses. Moreover, the Fe–TiO2 photocatalyst exhibited remarkable efficacy in degrading the targeted compound, trimethoprim (TMP), achieving an impressive degradation rate of 95.6 % within a concise 60-min timeframe and a captivating mineralization rate of 32.1 % within 120 min. These performance metrics outshone those of pristine TiO2 by substantial factors of 1.9 and 1.2, respectively. Photoelectric characterization results also confirmed that Fe doping significantly enhanced the efficiency of charge carrier separation of TiO2. Furthermore, the catalytic performance of Fe–TiO2 remains essentially unchanged after a tenfold expansion in equal proportion using the water bath doping system. This confirms the practicality of the batch preparation approach for Fe-doped TiO2. The Fe–TiO2 catalyst consistently demonstrated efficient degradation capabilities across various water sources, ranging from natural river water to treated secondary effluents from sewage plants and tap water, further emphasizing its significant potential for practical applications. This comprehensive study provides fresh insights into the batch preparation of doped catalysts and their utility in mitigating water pollution.

Investigating Fe-doped Ba0.67Ni0.33Mn1-xFexO3 (x = 0, 0.2) ceramics: insights into electrical and dielectric behaviors.

This study investigates the characteristics of the Ba0.67Ni0.33Mn1-xFexO3 perovskite compound, focusing on its structural and electrical aspects under varying Fe doping levels at the Mn-site (x = 0, 0.2). X-ray diffraction patterns confirm the material's consistent structure, with Fe3+ ions substituting Mn3+ ions while maintaining their identical ionic radius. Nano-crystallinity studies reveal single-phase crystallization in the orthorhombic structure with space group Imma. Samples are prepared through conventional solid-state sintering. The Williamson-Hall method calculates crystallite sizes, averaging 37 nm for x = 0 and 33 nm for x = 0.2. Electrical properties are examined using complex impedance spectroscopy at different temperatures and frequencies. Techniques such as energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) assess chemical composition. Activation energy values increase from 0.138 eV for x = 0 to 0.171 eV for x = 0.2, leading to reduced dc conductivity across the investigated temperature range. Dielectric permittivity enhances proportionally with increasing Fe doping. Variations in impedance profiles reveal a relaxation phenomenon. A circuit model, Rg + (Rgb//CPEgb), elucidates impedance data. This study illuminates the interplay between Fe doping, activation energy, and electrical conductivity in Ba0.67Ni0.33Mn1-xFexO3 perovskite, offering insights applicable to electronic and energy-related devices. Perovskite-based nanomaterials have diverse environmental applications, including solar cells, light-emitting devices, transistors, sensors, and energy storage.

Synergistic effects of Fe and Ag doping on the structural and optical properties of a TiO2 thin film: a dual function platform for hydrogen generation and dye degradation.

The global population is increasing at an alarming pace, leading to a rapid surge in industrialization and concomitant environmental degradation. In light of the present circumstances, it is crucial to find sustainable solutions to mitigate pollution and ensure a safe and clean environment for the present and future society. One promising solution is photocatalysis, which utilizes solar energy to address environmental issues while providing a renewable and sustainable energy source. Herein, a TiO2-based multi-layer thin film photocatalyst was developed, and its hydrogen generation and Rhodamine 6G dye degradation properties were analysed. As TiO2 undergoes excitation in the UV region, in order to shift the absorbance towards the visible region, bandgap engineering was performed with Fe and Ag doping. As a consequence, the band gap effectively reduces, and Fe and Ag doping result in the least gap energies measuring 2.7 eV and 2.85 eV, respectively. DFT band structure study was performed, which shows the presence of additional electronic states that lie in the conduction and valence energy bands of TiO2 owing to the doping of elements. Additionally, the effect of the number of thin film layers on photocatalysis was investigated. To confirm the presence of structural distortions and oxygen vacancies, different characterizations were performed.

Fe doping and interface engineering-induced dual electronic regulation of CoSe2/Co9S8 nanorod arrays for enhanced electrochemical oxygen evolution

Double electronic modification by Fe doping and interface engineering boosts the OER performance of Fe-doped CoSe2/Co9S8 nanorod arrays.

Preparation and characterization of Fe-ZnO cellulose-based nanofiber mats with self-sterilizing photocatalytic activity to enhance antibacterial applications under visible light.

Bacterial infections and antibiotic resistance have posed a severe threat to public health in recent years. One emerging and promising approach to this issue is the photocatalytic sterilization of nanohybrids. By utilizing ZnO photocatalytic sterilization, the drawbacks of conventional antibacterial treatments can be efficiently addressed. This study examines the enhanced photocatalytic sterilizing effectiveness of Fe-doped ZnO nanoparticles (Fe-ZnO nanohybrids) incorporated into polymer membranes that are active in visible light. Using the co-precipitation procedure, Fe-ZnO nanohybrids (Fe x Zn100-x O) have been generated using a range of dopant ratios (x = 0, 3, 5, 7, and 10) and characterized. The ability to scavenge free radicals was assessed and the IC50 value was calculated using the DPPH test at different catalytic concentrations. PXRD patterns showed a hexagonal wurtzite structure, which indicated that the particle size of the nanohybrid decreased as the dopant concentration rose. It was demonstrated by UV-vis diffuse reflectance experiments that the band gap of the nanohybrid decreased (redshifted) with Fe doping. The photocatalytic activity under sunlight increased steadily to 87% after Fe was added as a dopant. The Fe 5%-ZnO nanohybrid exhibited the lowest IC50 value of 81.44 μg mL-1 compared to ZnO, indicating the highest radical scavenging activity and the best antimicrobial activity. The Fe 5%-ZnO nanohybrid, which is proven to have the best photocatalytic sterilization activity, was then incorporated into a cellulose acetate polymer membrane by electrospinning. Disc diffusion assay confirmed the highest antimicrobial activity of the Fe 5%-ZnO nanohybrid incorporated electrospun membrane against Staphylococcus aureus (ATCC 25923), Streptococcus pneumoniae (ATCC 49619), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), and Candida albicans (ATCC 10231) under visible light. As a result, Fe 5%-ZnO nanofiber membranes have the potential to be employed as self-sterilizing materials in healthcare settings.

Flexible electrode of Fe-doped NiSe2@porous graphene as binder-free anode for lithium-ion batteries

Fe-doped NiSe2@porous graphene is prepared via filtration, annealing, and selenylation. The interfacial interaction between graphene and NiSe2 is enhanced by Fe doping and facilitates the transfer of lithium ions and electrons.