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Fe7S8 as a conversion‐type anode shows high capacity in lithium‐ion batteries (LIBs). Nevertheless, the sluggish ion transport rate, low electron conduction behavior, and large volume change upon cycling limit its applications in fast‐charging wide‐temperature‐range LIBs. Here, a simple hydrothermal and subsequent solid‐phase high‐pressure sulfidation route is proposed to synthesize a hollow Fe7S8/N‐doped C microsphere structure. The hollow space is enveloped by the spheres’ shell consisting of ultrafine Fe7S8 nanocrystals (≈8 nm) embedded into N‐doped C matrix, which enhances ion transport and electrical conduction, and accommodates the volume expansion of Fe7S8. Remarkably, in situ magnetometry reveals that spin‐polarized surface capacitance occurs during the stage of conversion reaction, in which the formed Fe and Li2S act as electrons and ions acceptor, respectively, to construct space charge zone at their interfaces, thus enhancing lithium transport and storage. Accordingly, the hollow microspheres show high gravimetric energy density and outstanding fast‐charging capability along with excellent cycling stability in Ah‐level pouch cells operating from ‐40 to 60 °C. For the first time, this work confirms the effectiveness of spin‐polarized surface capacitance effect on enhancing ion storage and transport in fast‐charging wide‐temperature‐range LIBs. [ABSTRACT FROM AUTHOR]

Developing high mass‐loading electrodes is crucial for enhancing the energy density of current batteries, yet challenges such as poor rate performance and cycling instability must be addressed. Spin charge storage on transition metal nanoparticle surfaces, characterized by rapid charging and the absence of phase transitions, offers an ideal storage behavior for high mass‐loading electrodes. In this study, electrospinning is utilized to fabricate free‐standing carbon nanofibers incorporating Co nanoparticles for high‐mass loading and high‐performance anodes. The resulting anode, with a maximum mass loading of 6.8 mg cm−2, exhibits remarkable cycle stability and high‐rate performance of 2 A g−1 at a capacity over 3 mAh cm−2, superior than reported results. Magnetometry and electron paramagnetic resonance spectroscopy are employed to monitor the charge storage mechanism of the Co@CNFs, involving both the reversible formation of a spin capacitance and the growth of radical anions in the solid electrolyte interface. Additionally, in situ X‐ray diffraction and optical microscopy provide direct evidence of the absence of mechanical stress‐induced phenomena within the spin charge process, attributed to high‐rate capable lithium storage under high mass loading. The strategic approach presented herein offers a reliable methodology for engineering high‐energy‐density lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

A study is performed of samarium-modified Fe-containing catalysts on aluminum–magnesium spinel (MgAl2O4) supports. Data on the adsorption and reduction properties of the catalysts, determined via in situ magnetometry and IR spectroscopy of adsorbed CO, are compared. The IR spectroscopy of adsorbed CO shows that the main Fe species which forms a bond with CO in unpromoted Fe/MgAl2O4 is Fe2+ cations on the surfaces of nucleation centers in both the oxide and the metal phase, while the contribution from complexes with Fe0 atoms is negligible. It is found that promotion with samarium in a ratio of Sm : Fe = 1 : 100 inside the catalyst contributes to the effective reduction of iron oxides. It is shown that the reduction of iron is greatest for the catalyst synthesized by depositing samarium on the surface of a Fe-containing catalyst. [ABSTRACT FROM AUTHOR]

Iron sulfide (FeS) has been extensively studied as sodium‐ion battery anodes due to its high theoretical capacity (609 mAh g−1), but its large volume expansion and low electrical conductivity result in unsatisfactory cycling life and poor rate performance. Moreover, the sodium ion storage mechanism of FeS at a voltage range of 0.01–1 V involving conversion reactions and subsequent ion storage process is unclear yet. Here, the study proposes a vapor‐pressure induced synthesis route to fabricate FeS/C yolk‐shell structure that ultrathin carbon layers coat on the surface of FeS nanosheets, which can accommodate volume expansion of FeS during sodiation observed via in situ transmission electron microscope and improve its electrical conductivity. Remarkably, an in situ magnetometry reveals that vast spin‐polarized electrons can be injected into superparamagnetic Fe nanoparticles (≈3 nm) formed during conversion reaction to induce evolution of electrode magnetization between 0.01 and 1 V, during which spin‐polarized surface capacitance effect occurs at Fe/Na2S interfaces to increase extra ion storage and boost ion transport stably. Consequently, the FeS/C yolk‐shell nanosheets deliver a high reversible capacity of 664.9 mAh g−1 at 0.1 A g−1, and 300.4 mAh g−1 after 10 000 cycles at 10 A g−1 with a capacity retention of 81.1%. [ABSTRACT FROM AUTHOR]

Abstract Transition metal fluorides (TMFs) cathode materials have shown extraordinary promises for electrochemical energy storage, but the understanding of their electrochemical reaction mechanisms is still a matter of debate due to the complicated and continuous changing in the battery internal environment. Here, we design a novel iron fluoride (FeF2) aggregate assembled with cylindrical nanoparticles as cathode material to build FeF2 lithium‐ion batteries (LIBs) and employ advanced in situ magnetometry to detect their intrinsic electronic structure during cycling in real time. The results show that FeF2 cannot be involved in complete conversion reactions when the FeF2 LIBs operate between the conventional voltage range of 1.0–4.0 V, and that the corresponding conversion ratio of FeF2 can be further estimated. Importantly, we first demonstrate that the spin‐polarized surface capacitance exists in the FeF2 cathode by monitoring the magnetic responses over various voltage ranges. The research presents an original and insightful method to examine the conversion mechanism of TMFs and significantly provides an important reference for the future artificial design of energy systems based on spin‐polarized surface capacitance.

A study is performed of cobalt/MgAl2O4 catalysts promoted with glucose at Co/C molar ratios of 16.5, 3.2, and 1.6 via sequential deposition and codeposition. Magnetometry and IR spectroscopy of adsorbed CO show that raising the content of carbon in the catalyst contributes to the reduction of cobalt, regardless of how Co is introduced. Infrared spectroscopy reveals the main adsorption sites are cobalt cations and metallic Co. A strong contribution from adsorption sites characteristic of large Co particles is observed in systems synthesized via codeposition. Adsorption sites attributed to Co2+ and Coδ+ are structurally more homogeneous than ones attributed to metallic Co. [ABSTRACT FROM AUTHOR]

Transition metal fluorides (TMFs) cathode materials have shown extraordinary promises for electrochemical energy storage, but the understanding of their electrochemical reaction mechanisms is still a matter of debate due to the complicated and continuous changing in the battery internal environment. Here, we design a novel iron fluoride (FeF2) aggregate assembled with cylindrical nanoparticles as cathode material to build FeF2 lithium‐ion batteries (LIBs) and employ advanced in situ magnetometry to detect their intrinsic electronic structure during cycling in real time. The results show that FeF2 cannot be involved in complete conversion reactions when the FeF2 LIBs operate between the conventional voltage range of 1.0–4.0 V, and that the corresponding conversion ratio of FeF2 can be further estimated. Importantly, we first demonstrate that the spin‐polarized surface capacitance exists in the FeF2 cathode by monitoring the magnetic responses over various voltage ranges. The research presents an original and insightful method to examine the conversion mechanism of TMFs and significantly provides an important reference for the future artificial design of energy systems based on spin‐polarized surface capacitance. [ABSTRACT FROM AUTHOR]

The problem of hydrogen storage in liquid organic hydrogen carriers is not only the choice of an appropriate organic substrate, but the development of a selective and active catalyst containing as low as possible noble metals. A synergistic effect of increasing conversion and selectivity in bicyclohexyl dehydrogenation to biphenyl on trimetallic Pt-Ni-Cr/C catalysts with an extremely low Pt loading (0.1 wt %), compared with bimetallic Ni-Cr/C and Pt/Ni/C systems, due to the supporting of platinum on nickel-chromium nanoparticles was established for the first time. The TOF values (mmol (H 2)/g Pt min) for hydrogen evolution under conditions of the reaction of bicyclohexyl dehydrogenation (320 °C, 0.1 MPa) on Pt supported onto a Ni-Cr/С composite exceed by two orders of magnitude the values found for the two-component catalysts. The maximum amount of the evolved hydrogen correlates to the selectivity of the complete dehydrogenation of bicyclohexyl into biphenyl on the Pt-Ni-Cr/C catalyst. The formation of a Ni-Cr solid substitution solution in a Ni-Cr composite deposited on a carbon carrier is shown by magnetometry, XRD, and TEM methods. [Display omitted] • Dehydrogenation of bicyclohexyl for hydrogen storage was explored. • Pt-Ni-Cr trimetallic catalysts were developed for dehydrogenation for the first time. • A synergistic effect of the metals on the conversion and selectivity was revealed. • The extremely low Pt loading was used in the catalysts. • The formation of a Ni-Cr solid substitution is shown by magnetometry and XRD. [ABSTRACT FROM AUTHOR]

Li-ion-based electric field control has been attracting significant attention, since it is able to penetrate deep into materials to exhibit diverse and controllable electrochemical processes, which offer more degrees of freedom to design multifunctional devices with low power consumption. As opposed to previous studies that mainly focused on single lithiation/delithiation mechanisms, we reveal three Li-ion modulation mechanisms in the same NiFe 2 O 4 spinel ferrite by in situ magnetometry, i.e ., intercalation, conversion, and space charge, which are respectively demonstrated in high, medium, and low voltage range. During the intercalation stage, the spinel structure is preserved, and a reversible modulation of magnetization arises from the charge transfer-induced variation of Fe valence states (Fe 2+ /Fe 3+ ). Conversion-driven change in magnetization is the largest up to 89 emu g -1 , due to the structural and magnetic phase transitions. Although both intercalation and conversion exhibit sluggish kinetics and long response times, the space charge manifests a faster switching speed and superior durability due to its interface electrostatic effect. These results not only provide a clear and comprehensive understanding on Li-based modulation mechanisms but also facilitate multifunctional and multiscenario applications, such as multistate memory, micromagnetic actuation, artificial synapse, and energy storage.

Abstract: The effect the nature of a carbon material characterized by activated charcoal and sibunit has on the chemical composition and dynamics of activation of Fe-containing catalysts in CO and syngas atmospheres is investigated. It is established that magnetite with Тθ = 572°С forms during the activation of Fe/Сact and FeCu/Сact in a CO flow; cementite with Тθ = 220°С forms during the activation of Fe/СSib and FeCu/СSib in a CO flow; and activation in a СО/Н2 flow results in the formation of Hägg carbide χ-Fe5С2 with Тθ = 257°С with all catalysts. [ABSTRACT FROM AUTHOR]

The formation kinetics of an ultrafine Fischer-Tropsch catalyst based on a cobalt-polyvinyl alcohol (Co-PVA) composite has been studied using in situ magnetometry. The CoO to Co reduction process has been investigated. It has been established that the kinetic data on cobalt reduction at the step of thermolysis of the Co-PVA precursor are best approximated by the two-dimensional diffusion mechanism. The particle size of the metal phase of the composite has been measured by magnetic granulometry, and this method has been shown to be applicable to determination of size characteristics. It has been found that cobalt particles are partially encapsulated inside the pyrolyzed matrix; the proportion of encapsulated particles is about 54%. [ABSTRACT FROM AUTHOR]

The physicochemical and catalytic properties of pyrolyzed cellulose-based Cu-Co solid dispersed composite catalysts synthesized by matrix isolation under the action of IR radiation have been studied. It has been shown that alcohols can be produced from CO and H in the presence of the synthesized composite catalysts comprising Cu-Co solid dispersed phase nanoparticles. The effect of synthesis conditions on the structure of the composite catalysts and their activity in synthesis gas conversion to alcohols has been studied by X-ray diffraction analysis, ATR-FTIR spectroscopy, and in situ magnetometry. [ABSTRACT FROM AUTHOR]

The electrochemical performance of electrode materials is largely dependent on the structural and chemical evolutions during the charge-discharge processes. Hence, revealing ion storage chemistry could enlighten mechanistic understanding and offer guidance for rational design for energy storage materials. Here, we investigate the mechanisms of potassium (K)-ion storage in the promising bimetal oxide materials by in situ magnetometry. We focus on a single-phased hollow FeTiO 3 (SPH-FTO) hexagonal prism synthesized through a complexing-reagent assisted approach and find that the K-ion storage in this compound occurs predominantly with an intercalation mechanism and fractionally a conversion mechanism. We also demonstrate a K-ion hybrid capacitor assembled with the prepared SPH-FTO hexagonal prism anode and activated carbon cathode, delivering a high energy density and high power density as well as extraordinary cycling stability. This new understanding is used to showcase the inherently high K-ion storage properties from the earth-abundant FeTiO 3 .

The presented study investigated the effects of temperature (350–650 °C) and gas environment (pure Ar versus a H2O/H2 partial pressure ratio (PH2O/PH2) of 5) on the extent of sintering and oxidation of Al2O3-supported Ni0 nanoparticles (≈4 nm). We note that a PH2O/PH2 of 5 corresponds to a simulated CO conversion of 94% during methanation. Sintering and oxidation were studied using in situ magnetometry, while ex situ TEM analyses confirmed the particle sizes before and after the magnetometry-based experiments. It was found that increasing the temperature from 350 to 650 °C in Ar at atmospheric pressure causes a negligible change to the average size and degree of reduction (DOR) of the starting Ni0 nanoparticles. However, studying the same temperature window under hydrothermal conditions at 10 bar causes significant particle growth (≈9 nm) and the development of a bimodal distribution. Furthermore, the presence of steam decreases the DOR of Ni0 from 86.2% after initial activation to 22.2% due to oxidation. In summary, this study reports on the expected sintering and oxidation of Ni-based catalysts under high CO conversion conditions at elevated temperatures during methanation. Importantly, we were able to demonstrate how magnetometry-based analyses can provide similar size information (and changes thereof) as those observed with TEM but with the added advantage that this information can be obtained in situ. [ABSTRACT FROM AUTHOR]