Stable Spinel Research Articles

Low Thermal Conductivity and Diffusivity at High Temperatures Using Stable High-Entropy Spinel Oxide Nanoparticles.

The realization of low thermal conductivity at high temperatures (0.11W m-1 K-1 800 °C) in ambient air in a porous solid thermal insulation material, using stable packed nanoparticles of high-entropy spinel oxide with 8 cations (HESO-8 NPs) with a relatively high packing density of ≈50%, is reported. The high-density HESO-8 NP pellets possess around 1000-fold lower thermal diffusivity than that of air, resulting in much slower heat propagation when subjected to a transient heat flux. The low thermal conductivity and diffusivity are realized by suppressing all three modes of heat transfer, namely solid conduction, gas conduction, and thermal radiation, via stable nanoconstriction and infrared-absorbing nature of the HESO-8 NPs, which are enabled by remarkable microstructural stability against coarsening at high temperatures due to the high entropy. This work can elucidate the design of the next-generation high-temperature thermal insulation materials using high-entropy ceramic nanostructures.

Unravelling the Relationship between Crystallographic Structure and Oxygen Evolution Reaction Activity of Nickel Cobalt Oxide Thin Films

The development of a sustainable energy system relies on the production of green hydrogen. One of the major challenges for water splitting is the synthesis of platinum group metal-free oxygen evolution reaction (OER) electrocatalysts. Spinel nickel cobalt oxides (NCOs) have attracted particular interest due to their stable electrocatalytic performance. The less researched rock-salt NCOs, however, are also promising due to their ability to convert to the OER-active hydroxide phase1. Further development of NCO electrocatalysts requires fundamental understanding of their crystallographic structure-OER performance relationship. This work addresses ~20 nm atomic layer deposited (ALD) NCO thin film systems with a broad composition range to unravel the above-mentioned relationship.Our previously developed ALD supercycle process2 based on Ni(MeCp)2, CoCp2 and O2 plasma is employed to generate a full range of chemical compositions, such that the phase transition from Ni-rich rock-salt films to Co-rich films at ~55 at.% Co can be observed. Extensive material characterisation reveals that the phase transition is accompanied by an increase in the +3/+2 ratio of the oxidation state of both Ni and Co. Electrochemical analysis in 1M KOH shows an optimal performance for the 30 at.% Co rock-salt film after 500 CV cycles and a synergistic effect between cobalt and nickel such that NCO films are more OER active than Co3O4 and NiO. The films show a composition-dependent activation during CV cycling, where a decrease in activation is observed for increasing Co at.%. No activation is observed for the spinel films. The activation is driven by bulk transformation to the active (oxy)hydroxide phase and is accompanied by an increase in electrochemical surface area (ECSA) up to a factor 8 for rock-salt films. The overpotential after cycling is corrected for the increase in ECSA using an original method, which reveals that Ni-rich spinel structure films are intrinsically more active3.The use of model systems in combination with extensive material characterisation and prolonged electrochemical testing allows us to distinguish two classes of NCO catalysts, the instantly active and highly stable Co-rich spinel films and the high surface area Ni-rich rock-salt phase which develops upon extensive activation . Placing these results in perspective, we conclude that application of these catalysts on high surface area 3D electrodes would benefit from the more intrinsically active spinel NCO films, whilst activated rock-salt films would be the preferred choice for thin film electrocatalysis studies. These results also show that rock-salt NCO films (<40 at.% Co) could be a more sustainable alternative to the more commonly used spinel NCO films. 1Gebreslase et al. J. Energy Chem. 2022, 67, 101-137 2van Limpt et al. JVSTA, 2023, 41, 032407 3van Limpt et al. Adv. Energy Mat. under review Figure 1

Unlocking the Potential of Lithium-Excess Spinel Cathodes for Next-Generation Li-Ion Battery Applications

The growing electric vehicle (EV) market necessitates the pursuit of cathode materials with enhanced energy density and economic viability. Currently, widely utilized cathode materials include LiMnxNiyCo1-x-yO2 (NMC), LiNixCoyAl1-x-yO2, and LiFePO4 (LFP). Despite nickel’s recognition as an abundant element, concerns have arisen regarding its demand and supply chain stability, potentially posing challenges to the cost-effectiveness of high-nickel cathodes.1 Conversely, while LiFePO4 exhibits cost-effective manufacturing, its limited energy density remains a bottleneck for enhancing EV range.2 Thus, there persists a substantial demand for the development of high energy density cathodes utilizing abundant elements.Mn stands out as an earth-abundant elements with significantly lower costs compared to Ni and Co. The history of Mn-based cathode development is notably extensive, including noteworthy examples like the spinel-structured LiMn2O4 and the layered lithium manganese rich cathode (LMR-NMC). These achievements collectively make Mn-based cathodes immensely appealing. Nevertheless, the traditional spinel-structured LiMn2O4 suffers from low operatable capacity due to the Jahn-Teller distortion caused by reduced Mn ions which hinders its further application. Although the LMR-NMC cathode exhibit impressively high capacity, it also suffers from voltage hysteresis and fading which inhibits the energy density and making it hard to control by the energy management system (EMS). Thus, there is still an imperative demand for development of next generation high energy density Mn rich cathode material.3 In 2021, our group have reported a novel Co-free lithium-excess spinel (LxS) structure cathode material denoted as LxS-Li2MnNiO4. The unique LxS-structured Li2MnNiO4 surpasses conventional spinels such as LiMn2O4 and LiMn1.5Ni0.5O4 by doubling the Li concentration in its pristine state, while maintaining its cubic symmetry. The Li/LxS-L2MnNiO4 cell exhibits remarkable performance, delivering ~225 mAh/g capacity from 2.5 – 5.0 V, with nearly 96% retention after 50 cycles. The exceptional electrochemical performance of LxS-Li2MnNiO4 is attributed to the stable spinel framework and the inherent 3D Li-ion diffusion pathways, facilitating rapid Li-ion diffusion.4 Recently, we synthesized a new series of Mn-rich LxS cathodes. These newly developed Mn-rich compounds exhibit an even better electrochemical performance, showcasing exceptional structural stability. The successful synthesis of high-performance Mn-rich LxS-LMNO not only broadens the compositional space of LxS materials but also positions them as promising, high-energy density, and cost-effective next generation cathode materials. (1) Wang, L.; Wang, J.; Wang, L.; Zhang, M.; Wang, R.; Zhan, C. A critical review on nickel-based cathodes in rechargeable batteries. International Journal of Minerals, Metallurgy and Materials 2022, 29 (5), 925-941.(2) Wang, Y.; He, P.; Zhou, H. Olivine LiFePO4: development and future. Energy & Environmental Science 2011, 4 (3), 805-817, 10.1039/C0EE00176G. DOI: 10.1039/C0EE00176G.(3) Gutierrez, A.; Tewari, D.; Chen, J.; Srinivasan, V.; Balasubramanian, M.; Croy, J. R. Earth-Abundant, Mn-Rich Cathodes for Vehicle Applications and Beyond: Overview of Critical Barriers. Journal of The Electrochemical Society 2023.(4) Shi, B.; Gim, J.; Li, L.; Wang, C.; Vu, A.; Croy, J. R.; Thackeray, M. M.; Lee, E. LT-LiMn 0.5 Ni 0.5 O 2: a unique co-free cathode for high energy Li-ion cells. Chemical Communications 2021, 57 (84), 11009-11012.

Effect of bias voltage on high-temperature oxidation resistance and electrical properties of Mn–Co coating with metal interconnects for solid oxide fuel cell

Abstract This study investigated the effects of bias voltage on the microstructure, high-temperature oxidation resistance, electrical conductivity, element diffusion, and barrier of chromium poisoning cathode of Mn–Co coating on the surface of SOFCs metal interconnect SUS441 ferritic stainless steel. A series of Mn–Co coatings were prepared by magnetron sputtering technique at different bias voltages (−10, −50, −90 V) and oxidized at high temperatures for 175 h at 850 °C in an air environment. The results showed that the surface of each coating before oxidation exhibited a cauliflower-like morphology, with the crystallinity of the coating increasing with higher bias voltage. After high-temperature oxidation, especially the Mn–Co coatings prepared at −90 V bias, a dense and stable MnCo2O4 spinel structure was formed, which is crucial in inhibiting the growth of the Cr2O3 oxide layer. In addition, the coating also exhibits excellent electrical conductivity (Ea = 0.35 eV), good high-temperature oxidation resistance (1.182 mg cm−2), and a stronger ability to prevent the diffusion of Cr elements.

Efficient extraction of refractory Cr from stainless steel dust by sodium persulfate oxidation roasting

Stainless steel dust (SSD) contains a high content of Cr and is listed as hazardous solid waste. However, SSD is mainly stockpiled in legacy waste sites due to its complexity and lack of investigation. Herein we comprehensively investigates the microscopic interaction between heavy metals and coexisting phases of SSD from the electric arc furnace (EAF). Furthermore, a new approach for extracting Cr from SSD was developed for the first time. It was found that SSD is enriched with Cr, Ni, Mn, and Zn. Most of these heavy metals are bound to stable spinel (e.g., FeCr2O4) and encapsulated by silicate. Using Na2S2O8 as the flux (1–24 mmol), under roasting at 350–750 °C in the air for 0.25–6 h, efficient heavy metal extraction can be achieved (Cr-80 %, Ni-86 %, Mn-93 %, Zn-94 %) at 650 °C for 1h. During the roasting processes, the silicate shell was broken, which facilitated the mass transfer of the oxidant. Fe(II) was oxidized to Fe(III) and collapsed the spinel structure, releasing the heavy metals during the following acid leaching. The total mass of SSD is reduced by 90–95 %, and detoxification of SSD is achieved after processing. In conclusion, efficient extraction refractory metals in SSD by Na2S2O8 roasting and the mechanism was elucidated for the first time. This method might also be applied for the treatment of other slags/ash waste that have a stable spinel structure and are encapsulated by silicate.

Enhanced thermal stability and corrosion resistance of novel high-entropy spinels in cryolite-alumina molten salt applications

The development of spinel oxide materials with high thermal stability and corrosion resistance is essential for thermochemical reactions, particularly in aluminum electrolysis. This study presents the structural design of a family of high-entropy spinels (HESs) with a stable cubic spinel structure (<i>Fd3‾m</i>), specifically formulated as (Cr5/12 Mn5/12 Fe5/12 Co3/8 Y3/8)3O4, (Y = Ni, Cu, or Zn). Our results demonstrate that these high-entropy spinels significantly outperform conventional NiFe₂O₄, exhibiting superior corrosion resistance and thermal properties. Specifically, we observe lower high-temperature weight loss (0.24 %–0.74 % at 1000 °C), reduced thermal conductivity (1.810–2.258 W m−1 K−1 at room temperature), and lower thermal expansion coefficients (8.2 - 10.7 × 10−6 K−1 from 400 °C to 800 °C), while maintaining comparable specific heat capacities (0.51–0.55 J g−1 K−1). Corrosion testing at 800 °C for 20 h in a KF3-AlF3-Al2O3 molten salt environment shows a corrosion layer thickness of less than 150 μm, with minimal corrosion product formation. These findings not only advance our understanding of material properties under extreme conditions but also pave the way for the development of next-generation materials for thermochemical applications, specifically aimed at improving the efficiency of aluminum electrolysis.

In-situ formation of spinel protective layer through extremely low K-doping for enhanced performance of Ni-rich layered cathodes

Herein, we demonstrate a novel and feasible strategy to stabilize the LiNi0.83Co0.12Mn0.05O2 (NCM) structure via the in-situ formation of a superficial spinel layer with potassium (K) doping. While K+ doped NCM is not new, the formation of the protective spinel layer gives surprising results with even a trace amount of doping, which is unique and novel, and nowhere reported. The structural transformation from layered to spinel on the surface region of NCM is achieved with a K-doping level of 0.05 mol% (NCM-0.05K) and the formed spinel layer acted as a protective pillar for stabilizing the host structure, leading to substantially improved electrochemical performance. The X-ray photoelectron spectra demonstrate a large increase in nickel (Ni2+) distribution after cycling for pristine but almost no change for the NCM-0.05K, suggesting a stable preformed spinel layer. The above results reveal that the K+ doping can strongly reduce the Ni4+ to stable Ni2+ under the spinel phase formation and improves cell performances in terms of specific capacity, capacity retention, rate capability, and Li+ diffusivity. The internal micro-cracking of host NCM is also effectively suppressed by the low amount of K doping. Excessive K-doping, in contrast, leads to a reduction in (de)lithiation rate and greater polarization.

(Keynote) Monodisperse Nanoparticles of Ternary Spinels for Electrochemical Energy Conversion and Storage

Ternary spinel nanoparticles are an exciting materials system that have been increasingly pursued for a variety of energy applications such as supercapacitors and as electrocatalysts for the oxygen reduction reaction. For example, Cobalt-manganese spinel oxides, in particular, have demonstrated outstanding performance as supercapacitors and electrocatalysts.Despite their exemplary performance in multiple electrochemical applications, there are few reports in the literature with high-quality ternary spinel nanoparticles, such as Co-Mn-O. Most reports show aggregated and polydisperse products that typically contain impurity phases like rock salt.In this work, we demonstrate the synthesis of monodisperse nanoparticles of ternary spinels using colloidal chemistry. To overcome challenges for ternary spinel oxides we use oxidized amines as a route to form the high-oxidation state complexes needed for stable spinel oxides, and modify the ligand binding to obtain colloidally stable nanoparticles. For the sulfide spinel system, we show the use of amino acids as a low-cost sulfur source. Finally, we extend this work to access high entropy nanoparticles for electrochemical applications.

Preparation of carbon-supported ruthenium spinel oxide catalyst and application thereof in the oxidation of 5-hydroxymethylfurfural.

Trivalent ruthenium (Ru) can catalyse the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). However, the structure of Ru itself is unstable and is prone to aggregation and oxidation, leading to a decrease in catalytic activity. Therefore, it is necessary to prepare a stable, reliable, Ru-based catalyst. Based on the catalytic properties of trivalent Ru, a stable spinel structure with zinc ferrite was designed and loaded onto different carbon supports to prepare a homogeneous and stable Ru-based catalyst. The structure and physico-chemical properties were characterized through scanning electron microscopy, X-ray diffraction, transmission electron microscopy and other techniques, and the catalyst was applied to the oxidation of HMF for the preparation of FDCA. The results show that the prepared magnetic activated carbon-supported Ru-based catalyst has a concentrated particle size distribution in the range of 5-8 nm, with a loading amount of 3.61 at%. It exhibits strong soft magnetism, which is beneficial for Ru loading. Additionally, it can be reused in the oxidation of HMF to prepare FDCA over 10 cycles, with the product yield remaining essentially unchanged. The catalyst prepared in this study is characterized by recyclability and structural stability, making it promising for practical applications.

Formation mechanism of large-sized CaO-SiO2-CaF2-Al2O3-MgO composite inclusions in super 304H stainless steel rods

Employing silicon deoxidation in the production of Super 304H stainless steel, large-sized CaO-SiO2-CaF2-Al2O3-MgO (CSFAM) composite inclusions are frequently observed in the rods, posing a substantial threat to product quality. This study delves into an analysis of the constituent phases of these large-sized inclusions, identifying the coexistence of liquid phase and spinel phase. Leveraging industrial experiments, systematic sampling of Super 304H stainless steel, and a comprehensive analysis involving dynamic and thermodynamic calculations, this study investigates the formation mechanism underlying such inclusions. The composition of inclusions in the sample before AOD tapping mirrors that of the slag, with high CaF2 content, indicating that they come from slag entrapment. Through kinetic calculations, it is indicated that the time of existence of the liquid film during the ascent of these inclusions is significantly longer than the collision time. This suggests that they are not easily removed and tend to persist in the steel. Despite LF refining, the predominant types of inclusions remain unchanged, and the decrease in temperature leads to the precipitation of solid-phase MgO within the inclusions. Solubility calculations for solid-phase MgO show a rising trend with temperature. Post-casting, MgO and Al2O3 content in inclusions increase, the solid-phase MgO region disappears, and in the subsequent cooling process, inclusions precipitate the stable spinel phase (MgAl2O4). Solubility calculations for solid-phase MgAl2O4 show a temperature-dependent increase. After the completion of casting, the steel ingot undergoes a deformation process through rolling, leading to the transformation of inclusions into large-sized, elongated, composite CSFAM inclusions.

Ultrasound‒induced facile synthesis of spinel CoFe2O4‒PAC magnetic nanocatalyst for remediation of hypersaline petrochemical wastewater: Degradation mechanism, biodegradability enhancement and phytotoxicity mitigation

In this study, magnetic CoFe2O4−PAC nanocatalysts were synthesized through facile hydrothermal and co‒precipitation approaches with ultrasonic irradiation, which were used for the treatment of hypersaline petrochemical wastewater (HPCW). When an ultrasound‒induced synthesis process (US@CoFe2O4‒PAC) was used, a more efficient and stable magnetic spinel CoFe2O4‒PAC nanocatalyst was developed. The application of this nanocatalyst as a PMS activator, not only caused eradication of 90.4% of chemical oxygen demand (COD) of a HPCW after 90 min reaction time under the optimum conditions (pH 5−6, catalyst dose 1.0 g/L and 1.0 mM PMS), but also led to marginal leaching of iron (314 μg/L) and cobalt (95 μg/L) from the nanocatalyst. Recycling experiments over five consecutive runs showed a negligible decrease (7.2%) in COD removal efficiency which proved the stability and reusability of magnetic US@CoFe2O4−PAC. Two main mechanisms of adsorption and catalytic oxidation processes (homogeneous and heterogeneous PMS) are involved simultaneously in the PMS/US@CoFe2O4−PAC system, which are responsible for the destruction of refractory contaminants of HPCW through the generation of SO4•‒ and OH• radicals. COD of HPCW was mainly removed through SO4•− radical attack (73.6%) and the biodegradability of HPCW was enhanced dramatically after 90 min reaction time. The germination index (GI) of raw HPCW was increased 17.1 ± 4.2% and 24.3 ± 8.8% after 15 and 90 min reaction time, respectively, even PMS/US@CoFe2O4−PAC system showed less impact on phytotoxicity mitigation. Hence, it can be recommended to dilute the effluent before using for irrigational purpose. The findings of this study present practical significance of spinel US@CoFe2O4−PAC, which is an environment‒friendly catalyst, easy to handle and can sustain long‒term operation for the treatment of recalcitrant hypersaline wastewater and the other potential practical applications.

Corrosion Behavior of Ni-Cr Alloys with Different Cr Contents in NaCl-KCl-MgCl2.

This study investigates the corrosion behavior of Ni-Cr binary alloys, including Ni-10Cr, Ni-15Cr, Ni-20Cr, Ni-25Cr, and Ni-30Cr, in a NaCl-KCl-MgCl2 molten salt mixture through gravimetric analysis. Corrosion tests were conducted at 700 °C, with the maximum immersion time reaching up to 100 h. The corrosion rate was determined by measuring the mass loss of the specimens at various time intervals. Verifying corrosion rates by combining mass loss results with the determination of element dissolution in molten salts using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Detailed examinations of the corrosion products and morphology were conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Micro-area elemental analysis on the corroded surfaces was performed using an energy dispersive spectrometer (EDS), and the elemental distribution across the corrosion cross-sections was mapped. The results indicate that alloys with lower Cr content exhibit superior corrosion resistance in the NaCl-KCl-MgCl2 molten salt under an argon atmosphere compared to those with higher Cr content; no corrosion products were retained on the surfaces of the lower Cr alloys (Ni-10Cr, Ni-15Cr). For the higher Cr alloys (Ni-20Cr, Ni-25Cr, Ni-30Cr), after 20 h of corrosion, a protective layer was observed in certain areas. The formation of a stable Cr2O3 layer in the initial stages of corrosion for high-Cr content alloys, which reacts with MgO in the molten salt to form a stable MgCr2O4 spinel structure, provides additional protection for the alloys. However, over time, even under argon protection, the MgCr2O4 protective layer gradually degrades due to chloride ion infiltration and chemical reactions at high temperatures. Further analysis revealed that chloride ions play a pivotal role in the corrosion process, not only facilitating the destruction of the Cr2O3 layer on the alloy surfaces but also possibly accelerating the corrosion of the metallic matrix through electrochemical reactions. In conclusion, the corrosion behavior of Ni-Cr alloys in the NaCl-KCl-MgCl2 molten salt environment is influenced by a combination of factors, including Cr content, chloride ion activity, and the formation and degradation of protective layers. This study not only provides new insights into the corrosion resistance of Ni-Cr alloys in high-temperature molten salt environments but also offers significant theoretical support for the design and optimization of corrosion-resistant alloy materials.

Spinel-stabilized layered LiCoO2 cathode by surface reconstruction strategy

Layered LiCoO2 (LCO) is one of the most successful cathode materials for lithium ion battery due to its high theoretical capacity and high compacted density. Nevertheless, However, several detrimental issues including surface degradation, destructive phase transformation, and inhomogeneous reactions, resulting in rapid capacity fading and short cycle life. Herein, a highly conformal and compatible spinel Li1-xCo2O4 was in situ reconstructed on LCO surface (S-LCO), which can be realized by thermal treating of in situ engineered LiCoO2@ZIF-67 composite experimentally. The intense and stable LiCoO2 and spinel Li1-xCo2O4 can promote rapid Li + transport and relieve the mechanical stress. Protected by the spinel Li1-xCo2O4, the optimized S-LCO harvests an initial reversible capacity of 171.9 mA h g−1 at 0.2 C within 4.5 V and offers 137 mA h g−1 at 1 C after 200 cycles with 77.0 % capacity retention (LCO: 68.5 mA h g−1 with 43.9 % capacity retention). The in situ XRD and ex situ SEM characterizations indicate that the spinel Li1-xCo2O4 can effectively enhance phase transformation reversibility (H1→H2→M1→H3→M2) without serious cell shrinkage and microstructure collapse. The feasible surface reconstruction strategy broadens the perspective for developing high-performance LCO-based cathodes.

An investigation into the impact of CuAl2O4 hydrophobization on catalyst structure and performance for syngas conversion

The intricate structure and surface properties of metal oxide catalysts pose a challenge for implementing hydrophobic surface treatment. Herein, the surface of CuAl2O4 catalysts is modified by means of grafting and bridging different saturated fatty acid molecules, including lauric acid, palmitic acid and stearic acid. Consequently, the modification leads to an enhancement in the hydrophobicity of the catalyst, as evidenced by an increase in the static water contact angle from 15.26° to 150.74°. The hydrophobization of CuAl2O4 catalysts, in turn, influences the decomposition and reduction capacity of CuAl2O4, thus favoring the formation of a more stable defective spinel structure and improving the dispersion of Cu particles, thereby restraining aggregation. Notably, the activity results indicate that the hydrophobically modified CuAl2O4 exhibits higher CO conversion and selectivity of dimethyl ether, while effectively suppressing the water–gas shift reaction and reducing CO2 selectivity. This observation points to the significance of the catalyst surface hydrophobicity in enhancing catalytic performance.

Unlocking the Value of End-of-Life JÜLICH Solid Oxide Cell Stack Interconnect Assembly: A Combined Experimental and Thermodynamic Study on Metallic Resource Recyclability

The present study provides fundamental information on the resource recyclability of the interconnect assembly, i.e., the steel interconnector and the nickel meshes, from an end-of-life JÜLICH Solid Oxide Cell Stack—F10 design. The interconnector is composed of iron, chromium, and less than 4 wt.% of other alloying elements, mainly cobalt and manganese. Calculated blended compositions with the nickel meshes revealed their potential as a raw material in the production of 4xx, 2xx, or 3xx stainless steels. The melting behavior of the interconnect assembly was investigated under different conditions, i.e., in inert and oxidizing atmospheres, with and without the addition of slag-forming fluxes. The results demonstrated preferential oxidation of chromium in a trivalent state within the stable cubic spinel phase. Finally, the experimental results were compared with the thermodynamic equilibrium calculations based on the available databases (FToxid, SGTE, and SGPS) in FactSage 8.1 software. The calculated tendency to oxidize is in the order of Cr &gt; Mn &gt; Fe &gt; Co &gt; Ni at P(O2) greater than 10−10 bar, validating the experimental results.

Engineered oxidation states in NiCo2O4@CeO2 nanourchin architectures with abundant oxygen vacancies for enhanced oxygen evolution reaction performance

Sluggish oxygen evolution reaction (OER) as the half reaction of water electrolysis hindered the production of clean hydrogen, necessitates a cost-effective electrocatalyst. Spinel nickel cobaltite (NiCo2O4), characterized by its lower cost, flexibility in oxidation states of cations, and stable spinel structure, holds promise as an OER electrocatalyst. However, there is still room for improvement in terms of its intrinsic electrochemical activity, conductivity, and active surface area. Inspired by the flexible valence states of Ni and Co, in this study, CeO2 was introduced into NiCo2O4 for further electronic structure adjustment. The result was the synthesis of an urchin-like NiCo2O4@CeO2 (NCOC), and the elucidation of its formation mechanisms, expressed conclusively through reaction formulas. NCOC, characterized by an open architecture and a rough surface, ensures rapid mass transportation and charge diffusion. Within NCOC, numerous oxophilic Ce3+ sites with oxygen vacancies construct electron transport pathways, accelerating charge-transfer. This simultaneously induces an increase in the oxidation states and proportions of Ni3+ and Co3+ in NCOC, reinforcing the covalence of Ni–O and Co–O bonds, expediting the ad/desorption of intermediates during OER. The electronic structure variations of NCOC were further verified through density functional theory (DFT) analyses, revealing alterations in adsorption configurations of intermediates and a decrease in adsorption free energies for intermediates on NCOC during OER. In practical terms, NCOC demonstrated a low overpotential of 228 mV at a current density of 10 mA cm−2 under 1 M KOH, maintaining long-term electrochemical stability for 100 h. Overall, this study provides a universal approach for designing highly cost-efficient electrocatalysts for OER.

Defect-rich hierarchical porous spinel MFe2O4 (M = Ni, Co, Fe, Mn) as high-performance anode for lithium ion batteries

Exploring innovative anode materials with excellent lithium storage capability is an urgent and challenging task. Among various candidates, the spinel ferrites based anodes received huge attention owing to the high theoretical capacity. However, the rapid capacity decaying and sluggish reaction kinetics during cycling have severely hampered their commercialization process. Herein, the hierarchical porous spinel MFe2O4 (M = Ni, Co, Mn, Fe), comprised of Mn doped porous NiFe2O4/CoFe2O4 heterostructure ligament network and Ni/Co/Mn co-doped Fe3O4 nanosheets network, is synthesized through a facile chemical dealloying strategy. The as-prepared MFe2O4 anode shows impressive cycling stability, revealing a discharge capacity of 1161.6 mAh g−1 after cycling for 1500 cycles at 500 mA g−1. Furthermore, the assembled LiFePO4//MFe2O4 full cell can display a reversible capacity of 111.2 mAh g−1 at 0.5 C after 150 cycles, exhibiting the great potential of the practical application of the MFe2O4 in the next-generation LIBs. The remarkable Li storage properties can be attributed to the particular hierarchical porous structure, highly active NiFe2O4/CoFe2O4 heterointerface and abundant surficial oxygen defects, high stable spinel structure contributed from high conformational entropy of polymetallic ions, and a double role of Mn doping in the cycling process. The structure regulating strategy proposed here is greatly expected to boost the developing of high-performance spinel ferrites based anodes.

Effect of oxide interactions on chromium speciation transformation during simulated municipal solid waste incineration

Chromium released during municipal solid waste incineration (MSWI) is toxic and carcinogenic. The removal of chromium from simulated MSWI flue gas by four sorbents (CaO, bamboo charcoal (BC), powdered activated carbon (PAC), and Al2O3) and the effects of four oxides (SiO2, Al2O3, Fe2O3, and CaO) on chromium speciation transformation were investigated. The results showed that the removal rates of total Cr by the four sorbents were Al2O3 < CaO < PAC < BC, while the removal rates of Cr(VI) by the four sorbents were Al2O3 < PAC < BC < CaO. CaO had a strong oxidizing effect on Cr(III), while BC and PAC had a better-reducing effect on Cr(VI). SiO2 was better for the reduction of Na2CrO4 and K2CrO4 above 1000°C due to its strong acidity, and the addition of CaO significantly inhibited the reduction of Cr(VI). MgCrO4 decomposed above 700°C to form MgCr2O4, and the reaction between MgCrO4 and oxides also existed in the form of a more stable trivalent spinel. Furthermore, when investigating the effect of oxides on the oxidation of Cr(III) in CrCl3, it was discovered that CaO promoted the conversion of Cr(III) to Cr(VI), while the presence of chlorine caused chromium to exist in the form of Cr(V), and increasing the content of CaO and extending the heating time facilitated the oxidation of Cr(III). In addition, silicate, aluminate, and ferrite were generated after the addition of SiO2, Al2O3, and Fe2O3, which reduced the alkalinity of CaO and had an important role in inhibiting the oxidation of Cr(III). The acidic oxides can not only promote the reduction of Cr(VI) but also have an inhibitory effect on the oxidation of Cr(III) ascribed to alkali metals/alkaline earth metals, and the proportion of acidic oxides can be increased moderately to reduce the generation of harmful substances in the hazardous solid waste heat treatment.

Using an Al-Incorporated Deep Black Pigment Coating to Enhance the Solar Absorptance of Iron Oxide-Rich Particles

The use of solid particles as direct heat absorbance and storage media promises enhanced storage densities in concentrated solar power (CSP) technologies. The long-term optical performance of those particles, which aim to be operational over years, is crucial. Dry powder coating with a deep black Cu-Mn-oxide pigment in a resonant acoustic mixer and subsequent sintering was employed to improve the long-term optical performance of hematite-rich spherical particles, which aimed to replace the state-of-the-art bauxite proppants. Due to the specific reactivity of the hematite particles, a new strategy using an Al-modified composition of the initial deep black pigment was required. The Al modification diminishes cation diffusion into hematite, allowing the formation of spinel-type Fe-Mn-Cu-Al-oxide coatings with favorable long-term temperature and optical stability. The effect of chemical composition of the coating layer on the coating process mechanism was discussed and the need for an elongated sintering time was noticed to ensure the termination of stable spinel phase formation. The structural and optical measurements revealed the enhancement of the properties of hematite absorber particles through this new modified coating process.

Surface ultrathin and uniform spinel structure induced by boron and fluorine dual doping for enhanced structure stability of Li-Rich layered oxides

Lithium-rich layered oxides (LLOs) cathode materials possess a highly desirable theoretical specific capacity owing to their special Li-O-Li units with unhybridized O-2p orbitals. However, LLOs suffer from some problems such as low initial coulombic efficiency (ICE), poor rate performance, and fast capacity decay owing to irreversible oxygen loss and structural decay during cycling. To address these issues, NH4BF4 (NBF) treatment is proposed to achieve dual doping with fluorine and boron while inducing a layered@spinel heterostructure on the surface of the LLO materials. The stable surface spinel layer protects the inner layered material from electrolyte corrosion and provide three-dimensional Li+ diffusion channels. The dual-doping of B and F alters the electronic structure, relieves internal charge hysteresis, and eventually inhibits irreversible oxygen release and transition metal migration by decreasing the energy bands of TM 3d-O 2p and non-bonding O-2p to lower energies. Consequently, the treated sample demonstrate an improved electrochemical performance with a high ICE of 90.0 % and a capacity retention of 91.0 % at 0.1 C after 100 cycles.