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Bifunctional catalysts for oxygen evolution reduction (OER) and oxygen reduction reaction (ORR) are key renewable energy technologies including metal–air batteries and water splitting. In this work, a solid-state sintering approach was employed to prepare spinel-structured bimetallic oxides Co2GeO4 and Ni2GeO4 with remarkable bifunctional catalytic activity. Compared to Ni2GeO4 and Co3O4, Co2GeO4 demonstrates a larger density of oxygen vacancies, leading to an increased abundance of active sites and superior OER and ORR activities. Electrochemical measurements were carried out in alkaline media, the material requiring a mere overpotential of 263 mV to attain a current density of 10 mA cm−2. Moreover, Co2GeO4 exhibited exceptional stability, maintaining a stable potential for 40 h at a current density of 1 mA cm−2. The calculation revealed that the high stability is attributed to the robust Ge-O bonds, which stabilize the Ge-O4 tetrahedrons within the spinel framework. This study possesses significant potential in guiding the development of highly efficient bifunctional electrocatalysts for both OER and ORR. [ABSTRACT FROM AUTHOR]

Magnetic field-assisted method has been proved as an effective method to improve oxygen evolution reaction performance (OER) of water splitting, however, the essential reason for the improvement of OER performance still remains unclear. Herein, Ni 1- x Zn x Fe 2 O 4 ferrites were prepared by the combination of hydrothermal and calcination method, the magnetic properties, oxygen evolution reaction performance and the effect of applied magnetic field on OER performance were studied and discussed according to the magnetic properties and ion site situation. The magnetic field effect depended on the applied magnetic field strength and the magnetic magnetization density of catalysts, it was attributed to changes of electron state and redistribution of ions in the spinel structure. The overpotential decreased by approximately 50 mV and its double layer capacitance increased about 60 % at 125 mT applied magnetic field. The results provided a newness research view for the domain of electrochemistry. [ABSTRACT FROM AUTHOR]

The degradation behaviors of three iridium-based oxides, SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 , in sulfuric acid solution for OER operation are investigated. It's discovered that the connection configurations of [IrO 6 ] octahedra units in the crystalline structure impact on the catalyst stability, in terms of the kinetics of cation dissolution, surface amorphization, bulk structure transformation, and etc. [Display omitted] • The degradation behaviors of three iridium oxides, SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 , are found to be strongly affected by the crystalline structure, particularly the inter-connection configurations of [IrO 6 ] octahedra units. • Sr2+ leaching leads to precipitation of non-conductive SrSO 4 on catalyst surface, which gradually blocks the reactive Ir sites. • The rapid formation of an amorphous IrO x surface layer can offer advantages in terms of electrochemical stability, preventing continuous leaching of Sr and Ir from the bulk structure. Large-scale hydrogen production by electrocatalytic water splitting still remains as a critical challenge due to the severe catalyst degradation during the oxygen evolution reaction (OER) in acidic media. In this study, we investigate the structural impacts on catalyst degradation behaviors using three iridium-based oxides, namely SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 as model catalysts. These Ir oxides possess different connection configurations of [IrO 6 ] octahedra units in their structure. Stable OER performance is observed on SrIrO 3 and attributed to the edge-linked [IrO 6 ] structure and rapid formation of a continuous IrO x layer on its surface, which functions not only as the "real" catalyst but also a shield preventing continuous cation leaching (with <1.0 at.% of Ir leaching). In comparison, both Sr 2 IrO 4 and Sr 4 IrO 6 catalysts demonstrate quick current fading with structure transformation to rutile IrO 2 and formation of inconducive SrSO 4 precipitates on surface, blocking the reactive sites. Nevertheless, over 60 at.% of Ir leaching is detected from the Sr 4 IrO 6 catalyst due to its isolated [IrO 6 ] structure configuration. Results of this work highlight the structural impacts on the catalyst stability in acidic OER conditions. [ABSTRACT FROM AUTHOR]

Nickel-based catalysts have been widely recognized as highly promising electrocatalysts for oxidation. Herein, we designed a catalyst surface based on iron oxide electrodeposited on NiCo2O4 spinel oxide. Nickel foam was used as a support for the prepared catalysts. The modified surface was characterized by different techniques like electron microscopy and X-ray photon spectroscopy. The activity of the modified surface was investigated through the electrochemical oxidation of different organic molecules such as urea, ethanol, and ethylene glycol. Therefore, the modified Fe@ NiCo2O4/NF current in 1.0 M NaOH and 1.0 M fuel concentrations reached 31.4, 27.1, and 17.8 mA cm−2 for urea, ethanol, and ethylene glycol, respectively. Moreover, a range of kinetic characteristics parameters were computed, such as the diffusion coefficient, Tafel slope, and transfer coefficient. Chronoamperometry was employed to assess the electrode's resistance to long-term oxidation. Consequently, the electrode's activity exhibited a reduction ranging from 17% to 30% over a continuous oxidation period of 300 min. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is a critical step for sustainable fuel production through electrochemistry process. Maximizing active sites of nanocatalyst with enhanced intrinsic activity, especially the activation of lattice oxygen, is gradually recognized as the primary incentive. Since the surface reconfiguration to oxyhydroxide is unavoidable for oxygen-activated transition metal oxides, developing a surface termination like oxyhydroxide in oxides is highly desirable. In this work, we demonstrate an unusual surface termination of (111)-facet Co3O4 nanosheet that is exclusively containing edge-sharing octahedral Co3+ similar to CoOOH that can perform at approximately 40 times higher current density at 1.63 V (vs RHE) than commercial RuO2. It is found that this surface termination has an oxidized oxygen state in contrast to standard Co-O systems, which can serve as active site independently, breaking the scaling relationship limit. This work forwards the applications of oxide electrocatalysts in the energy conversion field by surface termination engineering.

In this work, Ni-doped LiMn 2 O 4 spinel oxides were studied as the cathode materials of low temperature proton ceramic fuel cell. Increasing the content of doping Ni to 0.5, the calculated active energy of the polarization process of the cell decreased from 0.62 to 0.49 eV. The cell performance increased with the Ni doping of LiMn 2 O 4 cathode, and the optimal power density reached to 547 mW cm−2 at 550 °C with a low polar resistance of 0.42 Ω cm2 for LiNi 0.5 Mn 1.5 O 4. Ni partially replacing Mn at the B site could increase the content of Mn4+, resulting in the increase of oxygen vacancy content to maintain the charge balance, which is beneficial to the oxygen reduction reaction. These results demonstrate that spinel oxide could be a promising cathode material with highly oxygen reduction activity for advanced low temperature solid ceramic fuel cells. [ABSTRACT FROM AUTHOR]

Developing an efficient electrocatalyst for the oxygen electrode is a significant challenge in the field. In this study, Co–N co-doped carbon (denoted as CZIF-67) is used as modifier to enhance the catalytic activity of the spinel oxide NiCo2O4. Among all the catalysts synthesized, the composite catalyst containing 10% CZIF-67 (where CZIF-67 constitutes 10% of the total mass) exhibits the highest catalytic activity for both the oxygen evolution reaction and the oxygen reduction reaction. This is evidenced by the largest current densities of 275.6 mA·cm−2 and 235.6 mA·cm−2 at the cutoff voltage of 1.9268 V (vs. RHE) and 0.3268V (vs. RHE). XPS characterization showed the surface element composition and valence analysis of 10% CZIF-67, which revealed the synergistic reaction between CZIF-67 and NiCo2O4 to a certain extent. Electrochemical impedance spectroscopy (EIS) results indicate that the charge transfer resistance of 10% CZIF-67 catalyst is the lowest, suggesting a faster charge transfer rate. It can be attributed to the synergistic effects between appropriate amount of CZIF-67 and the spinel oxide NiCo2O4. Additionally, the large specific surface and the porous structure of CZIF-67 can provide more active sites for the reactions. [ABSTRACT FROM AUTHOR]

Nickel-based catalysts have been widely recognized as highly promising electrocatalysts for oxidation. Herein, we designed a catalyst surface based on iron oxide electrodeposited on NiCo2O4 spinel oxide. Nickel foam was used as a support for the prepared catalysts. The modified surface was characterized by different techniques like electron microscopy and X-ray photon spectroscopy. The activity of the modified surface was investigated through the electrochemical oxidation of different organic molecules such as urea, ethanol, and ethylene glycol. Therefore, the modified Fe@ NiCo2O4/NF current in 1.0 M NaOH and 1.0 M fuel concentrations reached 31.4, 27.1, and 17.8 mA cm−2 for urea, ethanol, and ethylene glycol, respectively. Moreover, a range of kinetic characteristics parameters were computed, such as the diffusion coefficient, Tafel slope, and transfer coefficient. Chronoamperometry was employed to assess the electrode’s resistance to long-term oxidation. Consequently, the electrode’s activity exhibited a reduction ranging from 17% to 30% over a continuous oxidation period of 300 min.

Energy storage applications received great attention due to environmental aspects. A green method was used to prepare a composite of nickel–iron-based spinel oxide nanoparticle@CNT. The prepared materials were characterized by different analytical methods like X-ray diffraction, X-ray photon spectroscopy (XPS), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM). The synergistic effect between nickel–iron oxide and carbon nanotubes was characterized using different electrochemical methods like cyclic voltammetry (CV), galvanostatic charging/discharging (GCD), and electrochemical impedance spectroscopy (EIS). The capacitances of the pristine NiFe2O4 and NiFe2O4@CNT were studied in different electrolyte concentrations. The effect of O H − concentrations was studied for modified and non-modified surfaces. Furthermore, the specific capacitance was estimated for pristine and modified NiFe2O4 at a wide current range (5 to 17 A g−1). Thus, the durability of different surfaces after 2000 cycles was studied, and the capacitance retention was estimated as 78.8 and 90.1% for pristine and modified NiFe2O4. On the other hand, the capacitance rate capability was observed as 65.1% (5 to 17 A g−1) and 62.4% (5 to 17 A g−1) for NiFe2O4 and NiFe2O4@CNT electrodes. [ABSTRACT FROM AUTHOR]

We report the development of a novel electrocatalyst composed of nanoarchitectured spinel cobalt manganese oxide and graphene for the oxygen reduction reaction (ORR). A combination of co-precipitation and hydrothermal methods achieved the unique nanoarchitecture of the electrocatalyst. The formation of CoMn2O4 electrocatalyst was confirmed by X-ray diffraction, transmission electron microscopy, and other spectroscopic and microscopic techniques. In addition to synthesizing CoxOy and MnxOy as control electrocatalysts, we created a physical mixture of CoMn2O4 and graphene to investigate the impact of their interface on electrocatalytic activity. Our findings indicate that CoMn2O4/graphene exhibits improved ORR activity, stability, and methanol tolerance in an alkaline medium. This enhancement can be attributed to the synergistic effect and strong interface interaction between CoMn2O4 and graphene. This study demonstrates the potential of the proposed electrocatalyst as a cost-effective and eco-friendly alternative for oxygen reduction in fuel cells applications. [ABSTRACT FROM AUTHOR]

{111}-Dominated octahedral Co 3 O 4 electrocatalyst with better adsorption performance and enhanced electron transfer exhibited good catalytic activity and high selectivity for glycerol oxidation to high-value-added chemical, i.e., dihydroxyacetone (DHA). [Display omitted] • Successful synthesis of the {111}- and {001}-dominant Co 3 O 4 electrodes. • First report of crystal engineering for the oxidation of glycerol using spinnel cobalt oxide (Co 3 O 4). • {111}-dominant octahedral Co 3 O 4 plane exhibits superior activity for glycerol oxidation. • Improved reactant adsorption, and charge transfer across distinct Co 3 O 4 facets all affect activity. To further explore the electrooxidation mechanism of biomass-based compounds, it is highly desirable to regulate the proportion of reactive facets and identify facet-governing reactivity through crystal facet engineering. In this study, octahedral and cubic cobalt spinel oxide (Co 3 O 4), each exclusively exposed by one specific type of facet, are selected as two representative microstructure models for tuning the selectivity and productivity of electrochemical glycerol oxidation reaction. The results indicate that the {111}-dominant octahedral Co 3 O 4 plane with a higher population of Co2+ sites exhibits superior electrocatalytic activity for glycerol oxidation compared with the {001}-dominant cubic Co 3 O 4 , allowing nearly 65% of glycerol to be converted into a high-value-added dihydroxyacetone (DHA) compound. The average DHA production rate over octahedral Co 3 O 4 (2.5 μmol cm−2h−1) are approximately 3.5 times greater than that over cubic Co 3 O 4 (0.7 μmol cm−2h−1). Electrochemical studies and surface atomic configuration analysis reveal that {111}-dominant octahedral Co 3 O 4 with a higher density of active cobalt ion yields unique reactant adsorption and charge transfer, leading to increased glycerol oxidation reactivity and productivity. The present study emphasizes the significance of controlling the highly active facet in developing efficient and selective electrocatalysts. [ABSTRACT FROM AUTHOR]

In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g−1. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g−1, an incredible discharge capacity of 543 mAh g−1 was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Chromium-based spinels with multiple mixed valence states have been considered as promising electrocatalysts. However, they are rarely reported as electrochemical sensors. Herein, spinel CoCr 2 O 4 nanocrystals with mixed redox couplings were controllably synthesized through a simple sol-gel method followed by air calcination at 500 °C and 600 °C. The X-ray photoelectron spectrum analyses reveal that CoCr 2 O 4 -500 and CoCr 2 O 4 -600 products possess different surface ratios of Co3+/Co2+ and Cr3+/Cr2+. Meanwhile, non-enzymatic H 2 O 2 electrochemical sensors were successfully fabricated by drop-coating the aforementioned nanomaterials onto the surface of bare glassy carbon electrode (GCE). Amongst, CoCr 2 O 4 -500/GCE shows high sensitivity (1016 μA mM-1 cm-2), low detection limit (150 nM) and wide detection range to H 2 O 2 in 0.1 M NaOH solution. These important indicators are better than those of CoCr 2 O 4 -600/GCE. It is also the first time to achieve highly sensitive detection of H 2 O 2 by pure chromite spinels so far. Such excellent electrochemical sensing performance stems from the synergistic effect of its large apparent electrode area, high electrical conductivity and proper surface ratio of mixed redox couplings for Co3+/2+/Cr3+/2+. Moreover, it also exhibits good selectivity, stability and recovery rate to trace H 2 O 2 in milk whey, mouthwash and contact lens cleaning solution. [Display omitted] [ABSTRACT FROM AUTHOR]

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode. [ABSTRACT FROM AUTHOR]

High catalytic efficiency and long‐term stability are two main components for the performance assessment of an electrocatalyst. Previous attention has been paid more to efficiency other than stability. The present work is focused on the study of the stability processed on the FeCoNiRu high‐entropy alloy (HEA) in correlation with its catalytic efficiency. This catalyst has demonstrated not only performing the simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high efficiency but also sustaining long‐term stability upon HER and OER. The study reveals that the outstanding stability is attributed to the spinel oxide surface layer developed during evolution reactions. The spinel structure preserves the active sites that are inherited from the HEA's intrinsic structure. This work will provide an insightful direction/pathway for the design and manufacturing activities of other metallic electrocatalysts and a benchmark for the assessment of their efficiency–stability relationship. [ABSTRACT FROM AUTHOR]

Different spinel composite oxide catalysts, LiMn2O4, ZnMn2O4 and CrMn2O4 are prepared and activities of the catalysts for selective catalytic reduction of NOx by NH3 (NH3-SCR) are tested at 50~450 ℃. The effects of catalyst structure, metal elements and valence states on NH3-SCR activity are investigated. The catalysts are characterized by physical adsorption instrument (BET), X-ray diffractometer (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR), etc. The structure-activity relationship of spinel catalyst is also studied. The results show that： The LiMn2O4 spinel catalyst has the best activity with more than 90% NO conversion at the space velocity of 6×104 mL/(g∙h) at 150 ℃, and it shows more than 80% NO conversion at 100~400 ℃, demonstrating good low temperature activity and wide temperature range. However, the denitrification activity of ZnMn2O4 and CrMn2O4 is relative poor, and the two have similar activities. In the presence of water, the activity of LiMn2O4 decreased greatly, while the activities of ZnMn2O4 and CrMn2O4 decreases slightly, showing better water resistance. The conversion rate of ZnMn2O4 reach 90% at 150 ℃, which is better than that of CrMn2O4 in the presence of water. Spinel ZnMn2O4 has a good NO conversion rate in a wide temperature range and strong water resistance. [ABSTRACT FROM AUTHOR]

Developing efficient and robust electrocatalysts is increasingly essential for water splitting, severely hindered by the sluggish four-electron transfer process of oxygen evolution reaction (OER). Amorphous/crystalline heterophase engineering has recently emerged as a promising electronic modulation approach for OER catalysts but suffers from poor conductivity of the amorphous structure. Here, we coupled the amorphous/crystalline NiFe2O4 induced by vanadium doping with NiP heterojunction, highlighting the synergistic effect in modulating the electronic structures and the complementary effect in promoting conductivity. As a superior electrocatalyst to commercial RuO2, the as-prepared NFO-V0.3-P showed a low overpotential of 277 mV at the current density of 20 mA cm−2, a Tafel slope of 45 mV dec−1, and long-term stability. The excellent OER catalytic activity is attributed to the synergistic effect at the heterophase interface with rich active sites, fine-tuning of electronic regulation, and enhanced conductivity.

A precise modulation of heterogeneous catalysts in structural and surface properties promises the development of more sustainable advanced oxidation water purification technologies. However, while catalysts with superior decontamination activity and selectivity are already achievable, maintaining a long-term service life of such materials remains challenging. Here, we propose a crystallinity engineering strategy to break the activity-stability tradeoff of metal oxides in Fenton-like catalysis. The amorphous/crystalline cobalt-manganese spinel oxide (A/C-CoMnOx) provided highly active, hydroxyl group-rich surface, with moderate peroxymonosulfate (PMS)-binding affinity and charge transfer energy and strong pollutant adsorption, to trigger concerted radical and nonradical reactions for efficient pollutant mineralization, thereby alleviating the catalyst passivation by oxidation intermediate accumulation. Meanwhile, the surface-confined reactions, benefited from the enhanced adsorption of pollutants at A/C interface, rendered the A/C-CoMnOx/PMS system ultrahigh PMS utilization efficiency (82.2%) and unprecedented decontamination activity (rate constant of 1.48 min-1) surpassing almost all the state-of-the-art heterogeneous Fenton-like catalysts. The superior cyclic stability and environmental robustness of the system for real water treatment was also demonstrated. Our work unveils a critical role of material crystallinity in modulating the Fenton-like catalytic activity and pathways of metal oxides, which fundamentally improves our understanding of the structure-activity-selectivity relationships of heterogeneous catalysts and may inspire material design for more sustainable water purification application and beyond. [ABSTRACT FROM AUTHOR]

Abstract High catalytic efficiency and long‐term stability are two main components for the performance assessment of an electrocatalyst. Previous attention has been paid more to efficiency other than stability. The present work is focused on the study of the stability processed on the FeCoNiRu high‐entropy alloy (HEA) in correlation with its catalytic efficiency. This catalyst has demonstrated not only performing the simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with high efficiency but also sustaining long‐term stability upon HER and OER. The study reveals that the outstanding stability is attributed to the spinel oxide surface layer developed during evolution reactions. The spinel structure preserves the active sites that are inherited from the HEA's intrinsic structure. This work will provide an insightful direction/pathway for the design and manufacturing activities of other metallic electrocatalysts and a benchmark for the assessment of their efficiency–stability relationship.

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important for developing energy systems such as fuel cells and metal–air batteries. Precious metal catalysts, such as Pt and IrO2, have been considered electrochemical catalysts because of their excellent activity for the ORR and OER. However, their disadvantages, such as low durability for long-term operation and high price, necessitate the development of alternative electrochemical catalysts. Transition metal oxides with excellent electrical conductivity, high efficiency, and stability have been considered alternative electrochemical catalysts owing to their ORR and OER activities, which are similar to those of precious metal catalysts. Therefore, in this study, composite catalyst materials comprising Co3O4 and CoFe2O4 spinel oxides were synthesized via hydrothermal synthesis. The synthesized composite oxides exhibit bi-functional electrochemical catalytic activity for ORR and OER owing to the large active surface area and increased number of oxygen vacancies via the nanostrain in Co3O4 nanoparticles. [ABSTRACT FROM AUTHOR]

A new spinel oxide CoFe 1.9 Li 0.1 O 4 (CFLO) has been synthesized as a cathode material for proton-conducting solid oxide fuel cells. CFLO has good structure stability up to 900 °C. In addition, the material can survive in both CO 2 and steam-containing atmospheres. Compared with the Li-free sample, the Li-doping strategy significantly regulates the material's electronic structure. The low valence of Li leads to the increased amount of Fe and Co cations with higher valences. Furthermore, doping Li creates more oxygen vacancies at the material surface, which benefits the oxygen reduction reaction (ORR). The improved cathode performance for CFLO has been demonstrated that a cell using CFLO cathode reaches a peak power density of 1052 mW cm−2 at 700 °C. The cell performance is 60% larger than the Li-free cell, and similar results can be detected at other testing temperatures. In addition, the CFLO cell shows good long-term stability in the working condition. This study proposes the Li-doping strategy to modify spinel oxides and also provides a new spinel oxide as a high-performing cathode for H–SOFCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electron-deficient tetrahedrally coordinated Co2+ sites were formed in reduced ZnCo 2 O 4. • R-ZnCo 2 O 4 exhibited a high NH 3 selectivity of 92.2 %, FE of 92.3 % and yield rate of 5.35 mg NH3 h−1 cm−2 (ca. 26.75 mg NH3 h−1 mg cat −1) under a low potential of − 0.3 V vs. RHE. • A Zn-NO 3 − battery was constructed and showed an open circuit voltage of 1.46 V and a peak-power density of 1.40 mW cm−2. Electrocatalytic NO 3 − reduction to ammonia (NRA) at ambient conditions emerges as an appealing solution for green ammonia synthesis. In this work, we prepared a reduced Co-based spinel oxide for efficient ammonia synthesis and energy conversion. The in-depth structural characterization and electrochemical evaluation revealed that the introduction of Zn and reduction treatment led to the formation of electron-deficient tetrahedrally coordinated Co2+ sites. The resulting R-ZnCo 2 O 4 exhibited remarkable NH 3 production capacity with high NH 3 selectivity of 92.2 %, FE of 92.3 %, and yield rate of 5.35 mg NH3 h−1 cm−2 (ca. 26.75 mg NH3 h−1 mg cat −1) under a low potential of − 0.3 V vs. RHE. The NRA pathway on R-ZnCo 2 O 4 was further elucidated through DFT calculations and in situ characterizations. The high NRA efficiency of R-ZnCo 2 O 4 was further explored in a Zn − NO 3 − battery, which was specified by an open circuit voltage of 1.46 V and a peak-power density of 1.40 mW cm−2, demonstrating its promising application for sustainable energy supply and green ammonia synthesis. [ABSTRACT FROM AUTHOR]

A novel process based on the microwave-edge-thermal effect (MET) was developed to construct three-dimensional (3D) self-supporting CoFe 2 O 4 /NF electrodes with a coral-like fractal structure as the promising OER electrocatalysts for water electrolysis to produce hydrogen under high-current–density (HCD) conditions. [Display omitted] • Microwave-edge-thermal effect was used to prepare coral-like CoFe 2 O 4 /NF electrodes. • The Coral-like structures highly improve the mass/charge transfer rates in OER. • This electrode is high-performance in AEM electrolyzer at a high current density. High-efficiency and long-term water-splitting to produce hydrogen under the high-current–density (HCD) environment is a severe challenge because the swift-consumption of electrolyte and large-production of bubbles require better charge/mass-transfer capability and durability of electrocatalysts. Rationally design and effectively construct of three-dimensional (3D) hierarchical electrocatalysts is the promising solutions to accelerate the charge/mass transfer rates during water splitting process. Herein, a 3D self-supporting coral-like oxygen evolution reaction (OER) electrode was synthesized using a microwave-edge-thermal (MET) effect induced heterogeneous-nucleation/oriented-attachment growth process by in-situ growing CoFe 2 O 4 nanocrystals on nickel-foams (CoFe 2 O 4 /NF). SEM, TEM, electrolyte/catalyst contact angles, in-situ observation of O 2 bubbles generation-evolution process, and three-electrode configuration (TEC) and anion-exchange-membrane (AEM) electrocatalytic OER tests at the HCD were used to investigated the structure–activity relationship of the CoFe 2 O 4 /NF electrode. The CoFe 2 O 4 /NF electrode offered super hydrophilic/aerophobic surfaces and firmly bonded interfaces, resulting in quicker charge/mass-transfer rates and long-term durability under the HCD conditions. The typical electrode exhibited a low OER overpotential of 0.24 V at 10 mA cm−2 and a Tafel slope of 35.2 mV dec−1; its alkaline AEM electrolyzer (Pt || CoFe 2 O 4 /NF) yielded a HCD of 1200 mA cm−2 at only 2.36 V and 60˚C and kept stable over 120 h. This work provides a new insight into the design and fabrication of active and stable non-noble metal-based OER electrocatalysts for cost-effective water-electrolysis applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The highly zincophilic Zn 2 TiO 4 nanoparticles were prepared for Zn anode protection. • The Zn 2 TiO 4 protective layer effectively suppresses the side reactions. • The Zn 2 TiO 4 nanoparticles effectively endow a dendrite-free and kinetics-enhanced Zn anode. The uncontrol growth of Zn dendrite and sluggish transport kinetics considerably hampered the practical application of aqueous zinc-ion batteries (AZIBs). Herein, we originally develop a simple and low-cost spinel oxide Zn 2 TiO 4 (ZTO) nanoparticle as a multifunctional artificial protective modulator to optimize the Zn anode. As verified by comprehensive experimental and theoretical analyses, the highly reactive ZTO modulator possesses prominent zincophilicity to preferentially adsorb Zn2+, accelerates the de-solvation and diffusion kinetics of Zn2+, and achieves uniform Zn2+ deposition by regulation the surface electric field distribution of Zn anode. Through this "adsorption-diffusion-deposition" process of Zn2+, a dendrite-free and kinetics-enhanced Zn metal anode was achieved. Consequently, the ZTO@Zn symmetric cell manifests the excellent reversibility, achieving 10,000 cycles plating/stripping processes at 20 mA cm−2 and stable cycling for more than 85 h even at 85 % depth of discharge. Notably, the ZTO@Zn||MnO 2 pouch cell exhibits an exceptional capacity of 215.9 mAh g−1 at 0.5 A g−1 and nearly 100 % coulombic efficiency after 300 cycles. This study provides a promising insight into the design of low-cost and highly reactive spinel oxide as an artificial protective modulator for Zn anode. [ABSTRACT FROM AUTHOR]

Typical infrared (IR) radiation materials, such as spinel structure with transition metal doping, remain challenges on IR radiation performance and thermal stability. Inspired by manipulatable entropy with desired properties, (Mg 1/5 Co 1/5 Ni 1/5 Cu 1/5 Zn 1/5)Al 2 O 4 (5MAl 2 O 4) with improved infrared radiation property and reduced thermal conductivity has been successfully synthesized. High-entropy strategy significantly narrows the band gap by impurity energy level formation, resulting in an improved 0.91 (0.78–2.5 μm). Simultaneously, 5MAl 2 O 4 emerges site inversion (tetrahedral and octahedral sites) and lattice distortion which benefits the outstanding infrared emissivity of 0.94 (2.5–15 μm, measured at 800 °C). Furthermore, 5MAl 2 O 4 reaches fairly low thermal conductivity of 2.1 W·m−1·K−1, 4–5 times decrease compared with MAl 2 O 4 end members. The remarkable infrared emissivity and low thermal conductivity offer great potential in energy conservation and heat dissipation. • Band gap narrowing and lattice distortion emerges in 5MAl 2 O 4. • The narrowed band gap of 5MAl 2 O 4 significantly promotes Near-IR radiation performance. • 5MAl 2 O 4 attains remarkable infrared emissivity of 0.91 (0.8–2.5 μm) and 0.94 (2.5–15 μm). • 5MAl 2 O 4 reaches fairly low thermal conductivity with 4–5 times decrease compared with MAl 2 O 4 end members. [ABSTRACT FROM AUTHOR]

Energy storage applications received great attention due to environmental aspects. A green method was used to prepare a composite of nickel–iron-based spinel oxide nanoparticle@CNT. The prepared materials were characterized by different analytical methods like X-ray diffraction, X-ray photon spectroscopy (XPS), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM). The synergistic effect between nickel–iron oxide and carbon nanotubes was characterized using different electrochemical methods like cyclic voltammetry (CV), galvanostatic charging/discharging (GCD), and electrochemical impedance spectroscopy (EIS). The capacitances of the pristine NiFe2O4 and NiFe2O4@CNT were studied in different electrolyte concentrations. The effect of OH− concentrations was studied for modified and non-modified surfaces. Furthermore, the specific capacitance was estimated for pristine and modified NiFe2O4 at a wide current range (5 to 17 A g−1). Thus, the durability of different surfaces after 2000 cycles was studied, and the capacitance retention was estimated as 78.8 and 90.1% for pristine and modified NiFe2O4. On the other hand, the capacitance rate capability was observed as 65.1% (5 to 17 A g−1) and 62.4% (5 to 17 A g−1) for NiFe2O4 and NiFe2O4@CNT electrodes.

In this work, Cu0.6Cd0.4Cr2O4 spinel oxide was synthesized by means of sol–gel auto-combustion route. The refined X-ray powder diffraction pattern confirmed the single-phase formation of the material, which crystallized in a cubic spinel structure with space group Fd-3 m. The alternating current conduction mechanism and modulus behavior of this sample were investigated over a broad frequency range (from 100 Hz to 1.6 MHz) for various temperatures ranging from 300 to 660 K. Two equivalent circuit models, R//C//CPE below 440 K and above this temperature R1//C1//CPE1 in series with R2//CPE2, were applied to fit the impedance data. The temperature dependence of the direct current conductivity could be described in terms of Arrhenius relation with four activation energies, 1.8 eV, 0.76 eV, 0.80 eV, and 0.98 eV, in regions I (T < 360 K); II (360–420 K); III (440–500 K); and IV (T > 500 K), respectively. The temperature and frequency dependence of AC conductivity was found to satisfy Jonscher's law (developed) at different temperatures. The variation of the exponent "s" with temperature strongly suggests that the conduction mechanism takes place by correlated barrier hopping (CBH) model in each region. A theoretical study of (AC) electrical conduction in this material has been interpreted using Elliot's theory, and Elliot's parameters are determined. For the modulus formalism, the extracted activation energies from the linear fit of ln(fp) as a function of 1000/T match well with those obtained from DC conductivity confirming that transport mechanisms were based on hopping phenomena. [ABSTRACT FROM AUTHOR]

We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode.

A series of 3D@2D constructed Al 2 O 3 @CoMn 2 O 4 microspheres with a hollow hierarchical structure supporting Pd nanoparticles was successfully synthesized by the the vertical in situ growth of 2D CMO spinel nanosheets on hollow Al 2 O 3 support. The introduction of core–shell hollow hierarchical structure leads to excellent catalytic activity for three kinds of VOCs, high stability and water-resistance and low-cost, making it a multifunctional and promising catalyst for VOC combustion. [Display omitted] • A series of 3D@2D constructed Al 2 O 3 @CoMn 2 O 4 microspheres with a hollow hierarchical structure was synthesized. • The introduction of hollow Al 2 O 3 for the in situ vertical growth of 2D CMO spinel materials leads to more accessible active sites and strengthening the interaction between them. • Theoretical calculations also indicate that the addition of Al 2 O 3 as the support material strengthens toluene and oxygen adsorption on CoMn 2 O 4. • The excellent catalytic activity for three kinds of VOCs, high stability and water-resistance and low-cost making it promising cadidate in practical application. • A possible catalytic mechanism of the as-synthesized catalyst was proposed. Catalytic oxidation is a promising method for removing harmful volatile organic compounds (VOCs). Therefore, exploring high-efficiency catalysts for catalyzing VOCs is of great significance to the realization of an environment-friendly and sustainable society. Here, a series of 3D@2D constructed Al 2 O 3 @CoMn 2 O 4 microspheres with a hollow hierarchical structure supporting Pd nanoparticles was successfully synthesized. The introduction of hollow Al 2 O 3 for the in situ vertical growth of 2D CMO spinel materials constructs a well-defined core − shell hollow hierarchical structure, leading to larger specific surface area, more accessible active sites and promoted catalytic activity of support material. Additionally, theoretical calculations also indicate that the addition of Al 2 O 3 as the support material strengthens the adsorption of toluene and oxygen on CoMn 2 O 4 , which promotes their activation. The dispersion of Pd further strengthens the low-temperature reducibility along with more active surface oxygen species and lower apparent activation energy. The optimum 1 wt% Pd/h-Al@4CMO catalyst possesses the lowest apparent activation energy for toluene of 77.4 kJ mol−1, showing the relatively best catalytic activity for VOC oxidation, reaching 100% toluene, benzene, and ethyl acetate conversion at 165, 160, and 155 °C, respectively. Meanwhile, the 1 wt% Pd/h-Al@4CMO sample possesses excellent catalytic stability, outstanding selectivity, and good moisture tolerance, which is an effective candidate for eliminating VOCs contaminants. [ABSTRACT FROM AUTHOR]

The development of low-cost and highly efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is a challenging topic in the fuel cells and metal-air batteries field. Herein, a noble metal-free composite consisting of nano-FeCoNi alloy and spinel oxide was successfully prepared through a simple one-step pyrolytic reduction strategy as identified by XRD, TEM, HRTEM, XPS, and other techniques. The effect of the reduction temperatures (700, 850, and 950 °C) on the composite structure as well as its OER/ORR performances was further investigated. It was observed that FeCoNi@Mn 2 AlO 4 was harvested at the temperature of 700 °C, while FeCoNi@MnAl 2 O 4 was finally formed when the reduction temperature was 850 °C and 950 °C. The composites showed comparable electrocatalytic performance to Pt/C in ORR as well as RuO 2 in OER. Moreover, all three catalysts showed great potential for bifunctional catalysis while FeCoNi@MnAl 2 O 4 -850 with a ΔEgap of 0.75 V, FeCoNi@MnAl 2 O 4 -950 with a ΔEgap of 0.77 V, and FeCoNi@Mn 2 AlO 4 -700 with a ΔEgap of 0.83 V. Density functional theory (DFT) computations further confirmed the synergistic effect between FeCoNi and MnAl 2 O 4. This work provides a facile approach to prepare an alternative bifunctional composite electrocatalyst for ORR/OER with deep understanding on the structure-performance relationship. [Display omitted] • A one-step pyrolytic reduction strategy was explored for composite synthesis. • Three noble metal-free FeCoNi alloy@spinel oxide composites were developed. • The reduction temperatures affected both structure and OER/ORR performance. • The composite catalyst has high ORR/OER catalytic activity and excellent stability. [ABSTRACT FROM AUTHOR]

Significant advancements towards enhancing the catalytic activity of spinel ferrites in oxygen evolution reaction (OER) have been achieved, however, further studies are required on this regard. In this study, Cr-doped spinel ferrite (NiFe 2 O 4) embedded in N-doped C (Cr-NiFe 2 O 4 @NC) was synthesized via a high-temperature treatment using an NiFe Prussian blue analog as a precursor and K 2 Cr 2 O 7 as a Cr source. Owing to the strong octahedral site preference energy, Cr3+ ions were successfully doped into octahedral sites and tailored the electronic configuration of NiFe 2 O 4 , as confirmed by XPS. The Cr-substituted Cr-NiFe 2 O 4 @NC exhibited the overpotential of 241 mV at 10 mA cm−2, which was smaller than that of NiFe 2 O 4 @NC (266 mV) at the same current density. Meanwhile, the Tafel slope of Cr-NiFe 2 O 4 @NC (65.32 mV dec−1) was also lower than that of NiFe 2 O 4 @NC (86.96 mV dec−1). Therefore, the Cr substitution can improve the electrocatalytic OER performance of NiFe 2 O 4 @NC. In particular, an assembled rechargeable Zn-air battery using Cr-NiFe 2 O 4 @NC as the cathode catalyst afforded a high power density (61.1 mA cm−2) together with a high specific capacity (740 mA g−1). Amazingly, it could power light-emitting diodes, demonstrating its real-world application. Density functional theory calculations revealed that Cr ion doping led to electron transfer in NiFe 2 O 4 , resulting in a density of electronic states close to the Fermi level, which probably regulated the adsorption/desorption behaviors of oxygenate intermediates (*O and *OOH), thus promoting the reaction kinetics of the OER. This study provides a helpful basis for the development of spinel oxides with high electrocatalytic OER activity and durability via cation doping. [Display omitted] • Cr-NiFe 2 O 4 @NC was prepared from NiFe Prussian blue analogue (NiFePBA). • The Cr dopant regulated d-band center position of NiFe2O4 for improving electrocatalytic OER activity. • The connection between Cr doping and OER activity was clarified by DFT. [ABSTRACT FROM AUTHOR]

• NiCo 2 O 4 @C hollow nanocages exhibited confinement effect. • Electron reconfiguration between Ni and Co enlarged the Co2+/Co3+ ratio. • In-situ generated carbon served as "electron shuttles" to accelerate electron transfer. • NiCo 2 O 4 @C showed exceptional Fenton-like catalytic activity and reusability. • Non-radical pathway dominated the NiCo 2 O 4 @C/PMS system. Spinel oxides are recognized as promising Fenton-like catalysts for the degradation of antibiotics. However, the catalytic performance is restrained by the poor electron transfer rate (ETR). Herein, hollow NiCo 2 O 4 @C nanocages are rationally designed and prepared to accelerate ETR in peroxymonosulfate (PMS) activation for tetracycline (TC) degradation. Enhanced ETR of the NiCo 2 O 4 @C/PMS system is due to three aspects: (1) The hollow nanocage facilitates the diffusion and adsorption of TC, improving the ion transfer at a macroscopic level; (2) Electron reconfiguration in octahedral sites of NiCo 2 O 4 increases the ratio of Co2+, resulting in highly efficient PMS activation; (3) In-situ generated carbon acts as "electron shuttles", improving the electrical conductivity of catalysts at a microscopic level. As a result, the NiCo 2 O 4 @C demonstrates rapid ETR, leading to a high-efficiency activation of PMS. The NiCo 2 O 4 @C/PMS system exhibits exceptional TC degradation efficiency and reusability. Non-radical pathway, including 1O 2 and direct electron transfer, dominates the system. This work offers a feasible strategy for enhancing electron transfer in the Fenton-like system. [ABSTRACT FROM AUTHOR]

[Display omitted] • CuCo 2 O 4 spinel oxides nanoparticles embedded on Y zeolite were synthesized. • NH 3 -reduction and re-oxidation treatments facilitate the formation of CuCo 2 O 4. • The confined CuCo 2 O 4 exhibits excellent catalytic oxidation activity and stability. Morphology-controlled synthesis with a tailor-made structure is a promising approach to enhance the catalytic properties of inexpensive spinel oxides as a viable alternative to noble metals. AB 2 O 4 spinel oxides, particularly, have garnered significant attention in mitigating volatile organic compounds (VOCs) emissions. The catalytic performance of these oxides can be improved through the modification of tetrahedrally coordinated A sites. In this study, we present a novel strategy for the preparation of CuCo 2 O 4 spinel oxide nanoparticles embedded on Y zeolite. This involves the co-loading of Cu and Co oxides on Y zeolite, followed by successive treatment with NH 3 -reduction and re-oxidation. The resulting morphology-confined CuCo 2 O 4 spinel oxides exhibit significantly higher catalytic activities and stabilities for the oxidation of CH 3 OH compared to their unrestrained counterparts. Our exploration into the in-situ formation of spinel oxides on Y zeolite, along with an investigation into their catalytic oxidation mechanism, lays the foundation for the rational design of non-noble metal oxide VOC catalysts. [ABSTRACT FROM AUTHOR]

Photocatalysis is an effective means to convert CO2 and solar energy into high value-added chemicals. Herein, the surface gradient S doped CuCo2O4 microflowers were fabricated by an in situ topotactic engineering strategy. This photocatalyst presented CO2 photoreduction with a satisfying activity (5 h, 181 μmol) and stability (94.5% retention). Additionally, the theoretical calculations indicated the fomated M-S bond could be favorbale to facilitate the initial CO2⁎ binding and promote the formation of COOH⁎ intermediates. This work provides a novel strategy for the fabrication of effective photocatalysts and highlights an in-depth understanding of micro-level regulation towards photocatalytic overall performance.

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important for developing energy systems such as fuel cells and metal–air batteries. Precious metal catalysts, such as Pt and IrO2, have been considered electrochemical catalysts because of their excellent activity for the ORR and OER. However, their disadvantages, such as low durability for long-term operation and high price, necessitate the development of alternative electrochemical catalysts. Transition metal oxides with excellent electrical conductivity, high efficiency, and stability have been considered alternative electrochemical catalysts owing to their ORR and OER activities, which are similar to those of precious metal catalysts. Therefore, in this study, composite catalyst materials comprising Co3O4 and CoFe2O4 spinel oxides were synthesized via hydrothermal synthesis. The synthesized composite oxides exhibit bi-functional electrochemical catalytic activity for ORR and OER owing to the large active surface area and increased number of oxygen vacancies via the nanostrain in Co3O4 nanoparticles.

We demonstrate a liquid-phase crystallization of interdispersed metal hydroxides nanoparticles (NPs) (diameter < 10 nm), toward the versatile syntheses of highly concentrated colloidal dispersions of spinel oxides. ZnGa 2 O 4 was chosen as a representative system to demonstrate our strategy. Heating of precursory wetgels of hydroxide NPs, interdispersed in a quasi-double-hydroxide-state, induced the crystallization at 60–80 °C into ZnGa 2 O 4 NPs with a size of single nanometer. X-ray absorption fine structure (XAFS) analysis reveals that octahedrally coordinated Zn2+ in the hydroxide NPs decreased as the result of the crystallizations, and the amount of tetrahedrally coordinated Zn2+ increased. By the chelation of acetylacetone (acac) to tetrahedrally coordinated zinc species in crystalline oxides NPs, deflocculation of the wetgel was induced and then acac worked as a dispersion stabilizer. The present method can be also applied to ZnAl 2 O 4 and ZnFe 2 O 4 NPs, allowing to yield the colloidal dispersions of spinel oxides NPs with a size of single nanometers in diameter with high dispersion stability (over 1 week) under highly concentrated conditions (ca. 20–40 g/L). [Display omitted] • Colloidal dispersions of spinel oxides nanoparticle are synthesized by gel-sol method. • The resultant colloidal dispersions are stably suspended under highly concentrated conditions. • Double hydroxides-like precursor is crystallized to spinel oxides at low temperatures. [ABSTRACT FROM AUTHOR]

The high voltage spinel material LiMn1.5Ni0.5O4 (LMNO) has the potential to increase the energy density of lithium batteries. However, its battery performance suffers from poor long-term cycling and high-temperature stability. In order to overcome these limitations, we have studied the effect of partial substitution of Mn with Ti and LiMn1.5−x Ni0.5TixO4 (x = 0.05, 0.1, 0.3), LMNTO, materials have been synthesized in a newly modified sol-gel method and then characterized by TEM, SEM (EDX), AC Electrochemical Impedance Spectroscopy and Soft X-ray Spectromicroscopy. We have demonstrated that the long-term cycling limitation with these types of materials can be resolved and herein 2000 cycles at a high C-rate have been demonstrated in half cells. We have attributed this behavior to a possible charge compensation mechanism as evidenced by a Soft X-ray Spectromicroscopy study of delithiated LMNTO materials. This work takes high energy density batteries based on high voltage spinel material one step further towards commercialization, and it is believed that further improvement can be achieved using new electrolyte formulations.

In this work, we report the synthesis of FeCo2O4 nanostructure electro-active material through a double-hydroxide medium via a facile hydrothermal method. The obtained product was subjected to structural and morphological studies. Morphological images of FeCo2O4 material revealed rod-like structures. Electrochemical properties of the modified electrode were evaluated by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy techniques. The modified FeCo2O4 electrode delivered the highest specific capacitance of 393.5 F g−1 at a current density of 1 A g−1 in 2 M KOH aqueous electrolyte with battery-type faradaic behavior and excellent capacitive properties. Furthermore, the long cycling stability of the electrode was tested up to 1000 cycles under a constant current density of 2 A g−1. The novel synthetic route of FeCo2O4 preparation is a convenient potential means of obtaining secondary energy material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

In the context of a modern research, revise, and development of alternative energy sources, electrochemical systems occupy a significant and promising niche. An open for research issue related to electrochemical energy sources is the development and search for efficient, environmentally friendly, and cost-effective catalysts for fuel cell. A promising and applicable direction in this area is the investigation of mixed-type oxide catalysts, in particular catalysts with a spinel structure. In the present work, the spinel of NiCo2O4 composition and its composites, obtained by a simple co-precipitation method, were investigated using SEM, XRD, and N2 low-temperature adsorption–desorption methods. The catalytic activity of all the synthesized samples was studied during the sodium borohydride hydrolysis reaction. A significant correlation was found between the features of the obtained samples porous structure and their catalytic properties. As the data obtained showed, the synthesized samples have all the properties of an effective catalyst that can be used in electrochemical energy sources. [ABSTRACT FROM AUTHOR]

We mainly focused on synthesis of boron doped cobalt gallium oxide (B doped CoGa 2 O 4) nanoparticles. In the study, varied amount of B doped CoGa 2 O 4 nanopowders were produced employing Sol-Gel technique. The structural characterizations of the particles were performed using x-ray powder diffractometer (XRD) and x-ray photoelectron spectroscopy (XPS) measurements. Rietveld refinements were utilized to investigate B atom replacement and thus, the changes in lattice parameters. Furthermore, the reflectance and absorbance performances were measured by UV–visible spectrophotometer in order to determine electronic energy level configurations through the band gap. The relationship between crystal structural and formation of electronic energy levels was also investigated according to the locations of substituted B atoms. [ABSTRACT FROM AUTHOR]

Phase relations within the "FeO–V 2 O 3 " oxide system at 1473 K in the oxygen partial pressure range from 5.98 × 10−15 to 2.39 × 10−8 atm were determined using the chemical equilibrium and quench method followed by XRD and EPMA measurements. There exist four univariant equilibria and two invariant equilibria in the "FeO–V 2 O 3 " oxide system. According to the determined phase relations, a phase diagram of this system was constructed by plotting log ( p O 2 / a t m ) versus the molar ratio of V/(Fe + V). Furthermore, the magnetic properties of a series of spinel Fe 3- x V x O 4 compounds prepared under different oxygen partial pressures were measured at room temperature. It was revealed that Fe 3- x V x O 4 compounds with Fe/V larger than 1.2 are magnetic, and their magnetizations increase remarkably with the increasing of the molar ratio of Fe/V. In addition, for the Fe 3- x V x O 4 compound with fixed molar ratio of Fe/V, its saturation magnetization increases slightly with the increasing of the oxygen partial pressure in which the compound was prepared. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoMn spinel and Zn-substituted CoMn spinel oxides were fabricated. • Differences in reaction mechanism of acetone and propane oxidation were revealed. • Lattice oxygen activity and oxygen activation capacity promoted acetone deep oxidation. • High valence Mn species facilitated C-H dissociation and C 3 H 7 activation of propane. CoMn spinel (CoMn) and Zn-substituted CoMn spinel (ZnCoMn) oxides were fabricated for revealing mechanism differences in acetone and propane catalytic oxidation. The temperature-conversion profiles, intrinsic reaction rate and activation energy convinced that CoMn and ZnCoMn exhibited high catalytic performance for acetone and propane oxidation, respectively. Experimental and theoretical investigation revealed that deep oxidation determined the acetone conversion, while the degradation of propane was governed by the fracture of C-H bond and subsequently the activation of C 3 H 7. CoMn possessed more active lattice oxygen and superior oxygen activation capacity, allowing acetone to be directly converted into carboxylates without generating aldehydes. ZnCoMn with more high valence Mn species was conductive to the C-H bond dissociation and C 3 H 7 activation. This work revealed the mutual relations between structure–property of the spinel oxides and reactivity of the diverse VOCs, which provided new insights for the rational design of spinel oxides for catalytic oxidation of diverse VOCs. [ABSTRACT FROM AUTHOR]

The cathode properties are critical for solid oxide fuel cells (SOFCs) performance and a major challenge for commercialization. This study employs the impregnation method to produce uniformly distributed Mg-doped manganese-chromium spinel oxide nanoparticles infiltrated into a network on the Gd 0.1 Ce 0.9 O 1.95 (GDC) skeleton as SOFC cathodes. The effects of Mg doping on the performance of these nanostructured spinel oxides are investigated. Both experimental results and density functional theory (DFT) calculations demonstrate that Mg doping can optimize the electronic structure of the manganese-chromium spinel oxide, increase the oxygen vacancy concentration, and significantly enhance the electrical conductivity and oxygen reduction reaction (ORR) catalytic activity. The Mg-doped manganese-chromium spinel oxide cathode exhibits superior performance, with an area-specific polarization resistance of 0.33 Ω cm2 and a maximum power density of 976 mW cm−2 at 800 °C. Moreover, the nanostructures of the cathode barely change after 100 h of cell operation. These findings provide a new strategy for optimizing the performance of SOFC spinel oxide cathodes. • Mg doping lowers bandgap and facilitates oxygen vacancy formation of Mn–Cr spinel. • Mg-doped Mn–Cr spinel cathode exhibits superior performance. • Nanostructures of Mg-doped Mn–Cr spinel remain stable after 100 h cell operation. [ABSTRACT FROM AUTHOR]

Mn-doped spinel oxides MnxNi1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, and 1) were synthesized using the citric acid-assisted sol–gel method. The Mn0.5Ni0.5Co2O4 (x = 0.5) supported on carbon nanosheets, Mn0.5Ni0.5Co2O4/C, was also prepared using the same method employing NaCl and glucose as a template and carbon source, respectively, followed by pyrolysis under an inert atmosphere. The electrocatalytic oxygen reduction reaction (ORR) activity was performed in alkaline media. Cyclic voltammetry (CV) was used to investigate the oxygen reduction performance of MnxNi1−xCo2O4 (x = 0, 0.3, 0.5, 0.7, and 1), and Mn0.5Ni0.5Co2O4 was found to be the best-performing electrocatalyst. Upon supporting the Mn0.5Ni0.5Co2O4 on a carbon sheet, the electrocatalytic activity was significantly enhanced owing to its large surface area and the improved charge transfer brought about by the carbon support. Rotating disk electrode studies show that the ORR electrocatalytic activity of Mn0.5Ni0.5Co2O4/C proceeds via a four-electron pathway. Mn0.5Ni0.5Co2O4/C was found to possess E1/2(V) = 0.856, a current density of 5.54 mA cm−2, and a current loss of approximately 0.11% after 405 voltammetric scan cycles. This study suggests that the interesting electrocatalytic performance of multimetallic transition metal oxides can be further enhanced by supporting them on conductive carbon materials, which improve charge transfer and provide a more active surface area.