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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 reconstructed surface structure of Co‐based spinel oxides serves as the active site for oxygen evolution reaction (OER). However, the structural complexity of spinel oxides and surface dynamics during the OER hinder the understanding of the reconstruction mechanism and electronic structure of the active site. In this study, spinel Co3O4@(CoFeV)3O4 nanocube (CoFeV) is reported, a (001) facet‐defined spinel oxide comprising Co, Fe, and V deposited on the Co3O4 nanocube template to exclude facet‐dependent factors. Introducing highly dissoluble V cations accelerates the reconstruction process to enhance the electrocatalytic activity. CoFeV exhibited enhanced electrocatalytic activity (266 mV at 10 mA cm−2 in 1 M KOH) and durability (maintained stable electrocatalytic activity during a 200 h chronopotentiometry (CP) test at 100 mA cm−2) with significantly enlarged electrochemically active surface area (ECSA). The experimental and theoretical results demonstrated that V dissolution during catalysis induced oxygen vacancies, accelerating the surface reconstruction to highly active oxyhydroxide. Consequently, the anion exchange membrane water electrolyzer (AEMWE) of CoFeV as the anode exhibited a remarkable performance of 6.19 A cm−2 at 2.0 Vcell in 1 M KOH and robust durability for 96 h at a constant current density of 500 mA cm−2. [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]

An efficient removal of the photocatalysts used in the decontamination of water is crucial after its application beside its expected visible light sensitive activities. This study presents the synthesis of magnetically separable CuFe2O4 nanoparticles (CFNPs) with enhanced photoactivity under AM 1.5 G sunlight. A simple two-step process involving co-precipitation and hydrothermal treatment is employed, with subsequent annealing at temperatures from 200 °C to 1000 °C to synthesize the CFNPs. The characteristic features of the highest photoactive tetragonal phase of CFNP are confirmed by powder XRD studies with Rietveld refinement. This scheme strategically controls the growth of a highly photoactive tetragonal phase with predominant (224) facets over other less active facets in cubic CuFe2O4. Mott–Schottky analysis confirms the p -type semiconducting nature of CFNPs. A favourable direct optical band gap of 1.73 eV, as well as photoluminescence emission quenching for visible photons, show that the (224) oriented CFNPs are good photocatalysts in the visible spectrum with demonstrated organic dye degradations, including methylene blue and others. A density functional theory-based approach validates that the adsorption of such dye is thermodynamically more favourable on (224) facets of CuFe2O4 to facilitate the redox action by the excitons. [ABSTRACT FROM AUTHOR]

The catalytic performance of spinel oxide NiCo2O4 for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was investigated. It shows that NiCo2O4 synthesized via hydrothermal treatment at 90 ℃ followed by calcination at 350 ℃ exhibits excellent catalytic activity. Furthermore, Fe-doped MnO2 (marked as Fe-M) was introduced as a modifier to further improve the performance of NiCo2O4. As expected, the 20% Fe-M hybrid catalyst (NiCo2O4 modified with 20 wt% Fe-M) displays the best ORR and OER catalytic activity. This is evidenced by its high OER current density of 265 mA cm−2, high ORR current density of 220 mA cm−2, low OER Tafel slope of 119 mV dec−1, low ORR Tafel slope of 167 mV dec−1. These exceptional results can be attributed to the synergistic effect between NiCo2O4 and Fe-M. Based on synergistic effect, the 20% Fe-M hybrid catalyst exhibits the best catalytic activity for oxygen evolution reaction and oxygen reduction reaction. [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.

Herein, an interfacial electron redistribution is proposed to boost the activity of carbon‐supported spinel NiCo2O4 catalyst toward oxygen conversion via Fe, N‐doping strategy. Fe‐doping into octahedron induces a redistribution of electrons between Co and Ni atoms on NiCo1.8Fe0.2O4@N‐carbon. The increased electron density of Co promotes the coordination of water to Co sites and further dissociation. The generation of proton from water improves the overall activity for the oxygen reduction reaction (ORR). The increased electron density of Ni facilitates the generation of oxygen vacancies. The Ni−VO−Fe structure accelerates the deprotonation of *OOH to improve the activity toward oxygen evolution reaction (OER). N‐doping modulates the electron density of carbon to form active sites for the adsorption and protonation of oxygen species. Fir wood‐derived carbon endows catalyst with an integral structure to enable outstanding electrocatalytic performance. The NiCo1.8Fe0.2O4@N‐carbon express high half‐wave potential up to 0.86 V in ORR and low overpotential of 270 mV at 10 mA cm−2 in OER. The zinc‐air batteries (ZABs) assembled with the as‐prepared catalyst achieve long‐term cycle stability (over 2000 cycles) with peak power density (180 mWcm−2). Fe, N‐doping strategy drives the catalysis of biomass‐derived carbon‐based catalysts to the highest level for the oxygen conversion in ZABs. [ABSTRACT FROM AUTHOR]

As a sustainable valorization route, electrochemical glycerol oxidation reaction (GOR) involves in formation of key OH* and selective adsorption/cleavage of C−C(O) intermediates with multi‐step electron transfer, thus suffering from high potential and poor formate selectivity for most non‐noble‐metal‐based electrocatalysts. So, it remains challenging to understand the structure–property relationship as well as construct synergistic sites to realize high‐activity and high‐selectivity GOR. Herein, we successfully achieve dual‐high performance with low potentials and superior formate selectivity for GOR by forming synergistic Lewis and Brønsted acid sites in Ni‐alloyed Co‐based spinel. The optimized NiCo oxide solid‐acid electrocatalyst exhibits low reaction potential (1.219 V@10 mA/cm2) and high formate selectivity (94.0 %) toward GOR. In situ electrochemical impedance spectroscopy and pH‐dependence measurements show that the Lewis acid centers could accelerate OH* production, while the Brønsted acid centers are proved to facilitate high‐selectivity formation of formate. Theoretical calculations reveal that NiCo alloyed oxide shows appropriate d‐band center, thus balancing adsorption/desorption of C−O intermediates. This study provides new insights into rationally designing solid‐acid electrocatalysts for biomass electro‐upcycling. [ABSTRACT FROM AUTHOR]

Rapid population growth has resulted in rapid growth in industrialization to meet various human needs. As a result of this, huge volume of effluent is being generated from the industrial processes and released into the water bodies. These anthropogenic activities are often detrimental to human and aquatic lives. In this study, a modeling approach to evaluate the photocatalytic degradation of organic pollutants from industrial wastewater using spinel oxide is investigated. Four machine learning algorithms namely, linear regression, decision tree ensemble, medium Gaussian support vector machine, and exponential Gaussian process regression were employed. The parametric analysis of the predictors (particle size of the spinel oxides, the initial dye concentration, the amount of photocatalysts, the band gap, and the irradiation time) and the targeted output of the photocatalytic degradation efficiency shows that a non-linear relationship exists between the predictors and the targeted output. This was further confirmed by the linear regression model with R2 of 0.220. Besides, the decision tree ensemble and medium Gaussian support vector machine regression offer poor performances in predicting the photocatalytic degradation efficiency as indicated by R2 of 0.420 and 0.490, respectively. A superior performance in predicting the photocatalytic degradation efficiency was displayed by the exponential Gaussian process regression with R2 of 0.991. [ABSTRACT FROM AUTHOR]

Core‐shell Co3O4@CoO nanoparticles were prepared by calcination of rock‐salt CoO and fully characterized by PXRD, TEM and XPS measurements. XPS studies showed that the Co(III) cation concentration steadily increased and the OER activity of the resulting core‐shell Co3O4@CoO nanoparticles decreased with increasing calcination time, which was attributed to the increasing presence of catalytically inactive Co(III) cations. The decrease in OER activity was also observed for untreated CoO nanoparticles (1) after chronopotentiometric (CP) treatment at 10 mA cm−2 for 18 h. The IR and EEL spectra of the resulting nanoparticles are comparable to those of a fully oxidized Co3O4 sample (1–300), that was prepared by calcining of the CoO sample (1) for 1 h at 300 °C. [ABSTRACT FROM AUTHOR]

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]

Radiation exposure induces defects in the crystal structure, leading to alterations in the structural, optical, and morphological properties of metal oxides. These irradiated metal oxides have found extensive use in various household applications. In this particular investigation, carbon-coated nickel cobalt oxide/rGO nanocomposites were synthesized through ultrasonication. Subsequently, these nanocomposites were subjected to three different doses of gamma radiation using a 60Co source. Both un-irradiated and irradiated samples were subjected to characterization using FTIR, SEM, XRD, and UV-Vis spectroscopy. The FTIR analysis confirmed the presence of a spinel-type structure in NiCo2O4. SEM analysis revealed the presence of crumbled sheets of rGO, and the irradiation process caused a transformation of these stacked sheets into thinner sheets. XRD analysis indicated a decrease in crystalline size and an increase in dislocation density with higher doses of gamma irradiation. UV-Vis spectroscopy demonstrated a reduction in both direct and indirect optical band gaps as a result of gamma irradiation. Furthermore, it was observed that Urbach energy and refractive index increased with gamma irradiation. Based on these findings, it can be concluded that gamma irradiation has a significant impact on the morphological, structural, and optical properties of NiCo2O4/rGO@C nanocomposites. [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]

Protonic ceramic fuel cells (PCFCs) are more suitable for operation at low temperatures due to their smaller activation energy (Ea). Unfortunately, the utilization of PCFC technology at reduced temperatures is limited by the lack of durable and high-activity air electrodes. A lot number of cobalt-based oxides have been developed as air electrodes for PCFCs, due to their high oxygen reduction reaction (ORR) activity. However, cobalt-based oxides usually have more significant thermal expansion coefficients (TECs) and poor thermomechanical compatibility with electrolytes. These characteristics can lead to cell delamination and degradation. Herein, we rationally design a novel cobalt-containing composite cathode material with the nominal composition of Sr4Fe4Co2O13+δ (SFC). SFC is composed of tetragonal perovskite phase (Sr8Fe8O23+δ, I4/mmm, 81 wt.%) and spinel phase (Co3O4, Fd3̄m, 19 wt.%). The SFC composite cathode displays an ultra-high oxygen ionic conductivity (0.053 S·cm−1 at 550 °C), superior CO2 tolerance, and suitable TEC value (17.01 × 10−6 K−1). SFC has both the O2−/e− conduction function, and the triple conducting (H+/O2−/e−) capability was achieved by introducing the protonic conduction phase (BaZr0.2Ce0.7Y0.1O3−δ, BZCY) to form SFC+BZCY (70 wt.%:30 wt.%). The SFC+BZCY composite electrode exhibits superior ORR activity at a reduced temperature with extremely low area-specific resistance (ASR, 0.677 Ω·cm2 at 550 °C), profound peak power density (PPD, 535 mW·cm−2 and 1.065 V at 550 °C), extraordinarily long-term durability (> 500 h for symmetrical cell and 350 h for single cell). Moreover, the composite has an ultra-low TEC value (15.96 × 10−6 K−1). This study proves that SFC+BZCY with triple conducting capacity is an excellent cathode for low-temperature PCFCs. [ABSTRACT FROM AUTHOR]

The reasonable design and controlled synthesis of efficient and hollow nanocatalysts with plentiful heterointerface and fully exposed active sites to accelerate the electron transfer and mass transfer process for oxygen evolution reaction (OER) is highly desirable for water splitting by electrolysis. Herein, a metal‐organic framework (MOF)‐engaged strategy is developed to prepare Ce‐doped hollow mesoporous NiCo2O4 nanoprisms (NiCo2O4/CeO2 HNPs) for enhanced OER. Due to the advanced synthesis strategy generating a large number of interfaces between NiCo2O4 and CeO2, as well as modulated electrons of the active center by the synergistic action of multi‐metals, the obtained catalyst exhibits excellent OER performance with a small overpotential of 290 mV at current density (J) of 10 mA cm−2. Spinel/Perovskite hollow nanoprisms synthesized by a similar way demonstrates the versatility of our strategy. This work may provide new insights into the development of rare earth‐doped hollow polymetallic spinel oxide catalysts. [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]

In the bipolar-type alkaline water electrolysis powered by renewable energy, electrocatalysts are degraded by repeated potential change associated with the generation of reverse current. If an electrode has large discharge capacity, the opposite electrode on the same bipolar plate is degraded by the reverse current. In this study, discharge capacity of various transition metal-based electrocatalysts was investigated to clarify the determining factors of electrocatalysts on the reverse current and durability. The discharge capacities from 1.5 to 0.5 V vs. RHE (Qdc,0.5) of electrocatalysts are proportional to the surface area in most cases. The proportionality coefficient, corresponding to the specific capacity, is 1.0 C·m–2 for Co3O4 and 2.3 C·m–2 for manganese-based electrocatalysts. The substitution of Co3+ in Co3O4 with Ni3+ increased Qdc,0.5. The upper limit of theoretical specific capacity for Co3O4 is estimated to be 1.699 C·m–2, meaning the former and latter cases correspond to 2- and 1-electron reactions, respectively, per a cation at the surface. The discharge capacities of the elctrocatalysts increased because of the dissolution and recrystallization of nickel and/or cobalt into metal hydroxides. The increase in the capacities of Co3O4 and NiCo2O4 during ten charge–discharge cycles was below 2–9% and 0.5–38%, respectively. Therefore, if a cathode electrocatalyst with relatively low redox durability is used on the one side of a bipolar plate, it is necessary to control optimum discharge capacity of the anode by changing surface area and constituent metal cations to minimize the generation of reverse current. [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.

Magnetic spinel oxides have attracted extensive research interest due to their rich physics and wide range of applications. However, these materials invariably suffer suppressed magnetization, due to structural imperfections (e.g., disorder, anti‐site defects, etc.). Herein, a dramatic enhanced magnetization is obtained with an increasement of 5 µB/u.c in CoFe2O4 (CFO) through ionic liquid gating induced hydrogen doping. The intercalated hydrogen ions lead to both distinct lattice expansion of ≈0.7% and notable Fe valence state reduction through electron doping, in which ≈17% Fe3+ is reduced into Fe2+. These facts collectively trigger a site‐specific spin‐flip on tetrahedrally coordinated Co2+ sites that enhances the net ferrimagnetic moment nearly to its theoretical maximum for perfect CFO. [ABSTRACT FROM AUTHOR]

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]

Recently, the introduction of external fields (light, thermal, magnetism, etc.) during electrocatalysis reactions gradually becomes a new strategy to modulate the catalytic activities. In this work, an external magnetic field was innovatively employed for the synthesis progress of (Ni, Zn)Fe 2 O 4 spinel oxide (M-(Ni, Zn)Fe 2 O 4). Results indicated the magnetic field (≤250 ​mT) would affect the morphology of catalyst due to the existing Fe ions, inducing the M-(Ni, Zn)Fe 2 O 4 nanosphere particles to be uniform and coral-like nanorods. In addition, the electronic structure of the catalyst was regulated by the valence state of Fe, changing the bonding of metal to oxygen atoms in different spinel sites. The results manifested that the M-(Ni, Zn)Fe 2 O 4 requires a lower overpotential of only 67 ​mV to deliver 10 ​mA ​cm−2 for hydrogen evolution reaction (HER) in alkaline electrolyte. Moreover, M-(Ni, Zn)Fe 2 O 4 respectively as the anode and cathode electrode for the overall water splitting, the catalysis system requires a cell voltage of only 1.76 ​V to gain a current density of 50 ​mA ​cm−2, combining with an excellent discharging stability after 10 ​h. This work provides a facile synthesis strategy toward the design of efficient non-noble metal catalysts for alkaline HER and overall water splitting. [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.

The oxygen evolution reaction (OER) is crucial for producing sustainable energy carriers. Herein, Ir (5 mol.%) doped inverse‐spinel NiFe2O4 (Ir‐NFO) nanoparticles deposited on Ni foam (NF) by scalable solution casting are considered a promising OER electrocatalyst for industrial deployments. The Ir‐NFO/NF (with minimal lattice distortion by uniform Ir doping) provides an OER overpotential of 251 mV (intrinsically outperforming NFO/NF and benchmarking IrO2/NF) and extraordinary robustness over 130 days at 100 mA cm−2. In situ X‐ray absorption spectroscopy reveals oxidation only for Fe on NFO, whereas concurrent generation of higher‐valent Ni and Fe occurs on Ir‐NFO during OER. Density functional theory calculations further demonstrate that Ir substitutes the sublayer Ni octahedral site and switches the main active reaction center from FeOhFeTd bridge site (FeOFe) on NFO to NiOh–FeTd bridge site (NiOFe active motif) on Ir‐NFO for a co‐catalytic OER. This study sheds new light on precious‐metal doped Ni‐Fe oxides, which may be applicable to other binary/ternary oxide electrocatalysts. [ABSTRACT FROM AUTHOR]

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]

• Black spinel nanoparticle coating turns quartz sand into solar-absorbing and thermal energy storage material. • Solar-weight absorption increases from ∼0.4 to ∼0.9 by the black coating. • Thermal conductivity of the particle bed is similar or increased with the black coating. • Solar absorptance remains unchanged after 100-hr annealing at 800 °C in air and 24-hr abrasion test with ball milling. Solid particles based direct solar absorbing heat transfer fluid (HTF) and thermal energy storage (TES) material is gaining increasing interests for high-temperature concentrating solar power (CSP). However, there is no particulate material that simultaneously possesses the performance and cost metrics needed to achieve the target levelized cost of electricity of future CSP, including high solar absorptance, high thermal conductivity, good mechanical and thermal stability, and importantly, low cost. In this work, we demonstrate a facile and scalable method to turn low-cost quartz sand into a direct solar-absorbing HTF and TES material by coating a thin silica shell containing black spinel nanoparticles (Cu 0.5 Cr 1.1 Mn 1.4 O 4 and CuCr 2 O 4). The black coating increases the solar absorptances of the sand from ∼0.43 to ∼0.89. The coated quartz sand also shows excellent stability and nearly unchanged optical properties after 100-hr of isothermal annealing at 800 °C and up to 24-hr ball mixing with Yttria Stabilized Zirconia (YSZ) grinding balls. The measured effective thermal conductivity of the coated quartz sand increases 0.30 W m−1 K−1 to 0.65 W m−1 K−1 from 20 °C to 700 °C and is comparable to that of uncoated sand as well as Carbo ceramic particle beds currently used in CSP plants. The coating process could represent a cost-effective and generic strategy to enhance the solar absorptance of solid particles, and when applied on low-cost sand, could turn them into low-cost and high-performance HTF and TES media for future CSP systems. [ABSTRACT FROM AUTHOR]

Direct ammonia solid oxide fuel cell (DA-SOFC) is a promising device to realize high-efficiency NH3-to-power. In this study, we fabricate a series of cobalt-based spinel ACo2O4 (ACO, A = Zn, Fe, Ni) oxide as DA-SOFC cathodes using the citric acid complexing method. We prepare three cobalt-based spinel oxides with different A-site elements, i.e., Zn, Fe, and Ni, to establish the relationships between the valence and active site of ACO spinel oxide. The structural analysis based on XRD, XPS, TEC, and UV-Vis diffuse reflectance confirms that NCO exhibits smaller band gap, higher electronic conductivity, and better compatibility with electrolyte. The electrochemical results indicate that the cathodic surface of NCO containing rich Co3+ and Oads leads to better oxygen reduction reaction (ORR) activity. The maximum power density of the DA-SOFC using NCO cathode reaches 1.06 W·cm−2 at 800°C, superior to those of using ZCO (0.83 W·cm−2) or FCO (0.92 W·cm−2) cathode. Kinetic analysis based on the distribution of relaxation time (DRT) and electrochemical impedance spectroscopy (EIS) indicates O T P B + e − ↔ O T P B − is rate-limiting. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have been established widely owing to their significance in water electrolyzers, fuel cells and metal‐air batteries. The ORR electron transfer number have been calculated from K−L plot as 3.1 (Fe3O4/ N2−xC‐500), 3.8 (Fe3O4/N2−xC‐600), 3.6 (Fe3O4/N2−XC‐700) and 3.2 (Fe3O4/N2−XC‐800). At 3 mA cm−2, the half‐wave potential has been determined as 0.66 V (Fe3O4/N2−XC‐500), 0.76 V (Fe3O4/N2−XC‐600), 0.75 V (Fe3O4/N2−XC‐700) and 0.68 V (Fe3O4/N2−XC‐800). At 10 mA cm−2, the OER potential for Fe3O4/N2−XC‐500, Fe3O4/N2−XC‐600, Fe3O4/N2−XC‐700 and Fe3O4/N2−XC‐800 electrocatalysts were determined as 1.61, 1.58, 1.62 and 1.66 V, respectively. The ORR: OER electrode potentials were found to be 0.95, 0.82, 0.87 and 0.93 V for Fe3O4/N2−XC‐500, Fe3O4/N2−XC‐600, Fe3O4/N2−XC‐700 and Fe3O4/N2−XC‐800 electrocatalysts, respectively by using solar to hydrogen fuel device conversion scale. The ORR/OER Tafel slopes were calculated as 78/89 mV/dec (Fe3O4/N2−XC‐500), 73/78 mV/dec (Fe3O4/N2−XC‐600), 76/83 mV/dec (Fe3O4/N2−XC‐700) and 79/98 mV/dec (Fe3O4/N2−XC‐800). Among the new born oxygen vacancy (Vo) spinel oxide electrocatalysts, Fe3O4/N2−XC‐600 exhibit an exceptional oxygen electrode activity with 0.82 V in 0.1 M KOH due to robust double exchange interconnection (DEI) between stable magnetite spinel Fe3O4 and N2−XC. [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]