Spinel MnCo Research Articles

Influence of Cobalt and Cobalt–Manganese Oxide Coating Thickness Deposited by DLI-MOCVD as a Barrier Against Cr Diffusion for SOC Interconnect

The influence of cobalt and cobalt–manganese oxide coating thickness on its ability to be a good diffusion barrier against Cr outward diffusion was investigated for stainless steel interconnects (AISI 441) of a solid oxide cell (SOC). The coatings were all synthesized using a DLI-MOCVD (Direct Liquid Injection-Metal Oxide Chemical Vapor Deposition) hot wall reactor. The study shows that a minimum cobalt oxide thickness of 300 nm was needed to be a good diffusion barrier against Cr for the 500-h exposure test. This observation was linked to the Mn concentration reached in the cobalt spinel during exposure. Indeed, during exposure at high temperature, Mn diffused from the substrate into the cobalt coating and transformed cobalt spinel into Co-Mn spinel. Whereas pure cobalt spinel was a good Cr diffusion barrier, cobalt-manganese spinel, Co3-xMnxO4, was not when x > 2. The thickness of the cobalt coatings must be chosen so that the Mn quantity coming into it from diffusion from the substrate does not degrade the protectiveness of the coating.

Overcoming metals redox rate limitations in spinel oxide-driven Fenton-like reactions via synergistic heteroatom doping and carbon anchoring for efficient micropollutant removal

The transition metals redox rate limitations of spinel oxides during Fenton-like reactions hinder its efficient and sustainable treatment of actual wastewater. Herein, we propose to optimize the electronic structure of Co-Mn spinel oxide (CM) via sulfur doping and carbon matrix anchoring synergistically, enhancing the radicals-nonradicals Fenton-like processes for efficient water decontamination. Activating peroxymonosulfate (PMS) with optimised spinel oxide (CMSAC) achieved near-complete removal of ofloxacin (10 mg/L) within 6 min, showing 8.4 times higher efficiency than CM group. Significantly higher yields of SO4·− and high-valent metal species in CMSAC/PMS system provided exceptional resistance to co-existing anions, enabling efficient removal of various emerging contaminants in high salinity leachate. Specifically, sulfur coordination and carbon anchoring-induced oxygen vacancy synergistically improved the electronic structure and electron transfer efficiency of CMSAC, thus forming highly reactive Co sites and significantly reducing the energy barrier for Co(IV)=O generation. The reductive sulfur species facilitated the conversion of Co(III) to Co(II), thereby maintaining the stability of the catalytic activity of CMSAC. This work developed a synergistic optimization strategy to overcome the metals redox rate limitations of spinel oxides in Fenton-like reactions, providing deep mechanistic insights for designing Fenton-like catalysts suitable for practical applications.

Boosting catalytic combustion of diesel soot particles over potassium-promoted CoMn-Co3O4 dual spinel structure catalyst

Catalytic oxidation is an effective method to remove soot particles from diesel exhaust, and the key aspect of this technology is to develop highly effective catalysts. In this work, a potassium-promoted dual spinel structure was prepared for soot elimination with the self-sacrificing template strategy. The highest activity was presented by the CoMn-0.2 H-10%K catalyst under a loose contact mode, with the temperature of soot conversion reaching 90% and turnover frequency value of 365 °C and 3.76×10−3 s−1, respectively. The catalyst was found to have a high content of oxygen vacancy and a superior ability for lattice oxygen migration, which led to elevated performance for soot combustion. The formation of K-OMS-2 at the interface between the CoMn spinel and the Co3O4 spinel was one of the reasons for the elevated lattice oxygen migration at low temperatures. This work provides an effective way to prepare transition metal catalysts for soot combustion.

Local Electron Environment Regulation of Spinel CoMn2O4 Induced Effective Reactant Adsorption and Transformation of Lattice Oxygen for Toluene Oxidation.

In contrast to numerous studies on oxygen species, the interaction of volatile organic compounds (VOCs) with oxides is also critical to the catalytic reaction but has hardly been considered. Herein, we develop a highly efficient Pt atom doped spinel CoMn2O4 (Pt-CoMn) for oxidation of toluene at low temperature, and the toluene conversion rate increased by 18.3 times (129.7 versus 7.1 × 10-11 mol/(m2·s)) at 160 °C compared to that of CoMn2O4. Detailed characterizations and density functional theory calculations reveal that the local electron environment of the Co sites is changed after Pt doping, and the formed electron-deficient Co sites in turn strengthen the interaction with toluene. Adsorbed toluene will react with lattice oxygen in Pt-CoMn and CoMn catalysts and convert into benzoate intermediates, and the consumption rate of benzoate is closely related to the activation of gaseous oxygen. Significantly, the abundant bulk defects of Pt-CoMn help to open the reaction channel in the CoMn spinel, which acts as an oxygen pump to promote the transformation of bulk lattice oxygen into surface lattice oxygen at lower temperatures, thus accelerating the conversion rate of benzoate intermediates into CO2 and enhancing low-temperature combustion of toluene. Pt-CoMn developed here emphasizes the regulation of VOCs adsorption strength and lattice oxygen transformation processes on CoMn2O4 by adjusting the local electron environment, which will provide new guidance for the design of efficient oxide catalysts for catalytic oxidation.

New insight into opposite oxidation behavior in acetone and propane catalytic oxidation over CoMn based spinel oxides

CoMn spinel (CoMn) and Zn-substituted CoMn spinel (ZnCoMn) oxides were fabricated for revealing mechanism differences in acetone and propane catalytic oxidation. The temperature-conversion profiles, intrinsic reaction rate and activation energy convinced that CoMn and ZnCoMn exhibited high catalytic performance for acetone and propane oxidation, respectively. Experimental and theoretical investigation revealed that deep oxidation determined the acetone conversion, while the degradation of propane was governed by the fracture of C-H bond and subsequently the activation of C3H7. CoMn possessed more active lattice oxygen and superior oxygen activation capacity, allowing acetone to be directly converted into carboxylates without generating aldehydes. ZnCoMn with more high valence Mn species was conductive to the C-H bond dissociation and C3H7 activation. This work revealed the mutual relations between structure–property of the spinel oxides and reactivity of the diverse VOCs, which provided new insights for the rational design of spinel oxides for catalytic oxidation of diverse VOCs.

Fluorinated Poly(aryl piperidinium) Membranes for Anion Exchange Membrane Fuel Cells.

Anion-exchange-membrane fuel cells (AEMFCs) are a cost-effective alternative to proton-exchange-membrane fuel cells (PEMFCs). The development of high-performance and durable AEMFCs requires highly conductive and robust anion-exchange membranes (AEMs). However, AEMs generally exhibit a trade-off between conductivity and dimensional stability. Here, a fluorination strategy to create a phase-separated morphological structure in poly(aryl piperidinium) AEMs is reported. The highly hydrophobic perfluoroalkyl side chains augment phase separation to construct interconnected hydrophilic channels for anion transport. As a result, these fluorinated PAP (FPAP) AEMs simultaneously possess high conductivity (>150mScm-1 at 80°C) and high dimensional stability (swelling ratio <20% at 80°C), excellent mechanical properties (tensile strength >80MPa and elongation at break >40%) and chemical stability (>2000h in 3m KOH at 80°C). AEMFCs with a non-precious Co-Mn spinel cathode using the present FPAP AEMs achieve an outstanding peak power density of 1.31Wcm-2 . The AEMs remain stable over 500h of fuel cell operation at a constant current density of 0.2Acm-2 .

Catalytic combustion of propane over Mg-modified Co1.5Mn1.5O4 spinel catalysts: Boosting C-H cleavage with Lewis acid and oxygen vacancies

Rational modulation of surface electronic structure can optimize the adsorption and activation of reactant molecules on the catalyst surface, which is crucial for catalytic elimination of hydrocarbons. Herein, a facile low-valence Mg doping strategy was applied to synthesize highly active and stable Co-Mn binary oxide (CMO) catalyst. Lewis acid sites and oxygen vacancies were purposefully introduced on CMO through the surface electron deficit caused by the substitution of doped Mg for host metals. For the CMO catalyst modified by appropriate amount of Mg (CMO-Mg0.05), the Co-Mn spinel with lattice expansion is significantly modified through substitution of Co or Mn ions with Mg2+, resulting in generation of abundant higher metal oxidation state species (Co3+, Mn4+) and oxygen vacancies. The best performance for catalytic propane combustion was achieved on CMO-Mg0.05 catalyst, with the T90 at 255 °C under high space velocity (60,000 ml g−1 h−1). Meanwhile, clear improvements on stability and water resistance were also achieved after the modification of Mg in CMO catalyst. Combined with C3H8-TPD, in-situ DRIFTS and various characterizations, it can be revealed that the synergistic effect of Lewis-acid sites and oxygen vacancies would remarkably promote the process of propane dissociative adsorption and mineralization. This work not only gives insight into the Mg dopants in boosting CH activation on CMO catalyst, but also provides a potential strategy for fabricating highly active hydrocarbon combustion catalysts.

Strategy for oxygen vacancy enriched CoMn spinel oxide catalyst activated peroxodisulfate for tetracycline degradation: process, mechanism, and toxicity analysis.

Antibiotic-like organic pollutants are harmful to aquatic ecosystems and seriously disrupt the ecological balance. Herein, we propose a simple and versatile method to prepare cobalt-manganese oxides with high specific surface area and abundant oxygen vacancies using low-temperature reduction crystallization, which greatly facilitates the adsorption and electron transfer between the catalyst, PDS, and TC, thus accelerating the degradation of tetracycline (TC). Among them, the degradation efficiency of TC in the CoMn2O4(C)/PDS system was 99.8% in 60 min and the degradation rate remained above 90% after four cycles. The possible degradation mechanism is also discussed, where Co is the main metal active center of the catalyst and Mn plays an auxiliary catalytic role to promote the generation of reactive radicals in PDS through redox interactions between Co and Mn, where SO4 -˙ is the main active species for TC degradation. Finally, the possible degradation pathways of TC are proposed and the toxicity of the intermediates is evaluated. Findings from this work will shed light on the rational design of bimetallic oxide catalysts.

Coupled spinel manganese−cobalt oxide and MXene electrocatalysts towards efficient hydrogen evolution reaction

A convenient and cost-effective strategy is developed to the controllable fabrication of the small-sized spinel MnCo 2 O 4 nanocrystals strongly coupled with 2D Ti 3 C 2 T x MXene nanosheets, which express exceptional electrocatalytic ability towards the hydrogen evolution reaction. • Heterojunction catalysts made from spinel MnCo 2 O 4 and MXene are first synthesized. • Ultrafine MnCo 2 O 4 nanocrystals are homogeneously dispersed on the MXene surface. • The intimate 0D/2D interfacial connection enables strong electronic interactions. • The newly-designed catalysts show superior electrocatalytic ability for hydrogen evolution. Although nanostructured spinel oxides have been considered as potential electrode materials for the hydrogen evolution reaction (HER), their catalytic properties still need to be substantially improved to meet the requirements of practical use. In this work, we present the rational design and controllable synthesis of nanosized spinel manganese−cobalt oxide strongly coupled with ultrathin Ti 3 C 2 T x MXene nanosheets (MnCo 2 O 4 /Ti 3 C 2 T x ) through a facile and cost-effective strategy. The effective combination of spinel MnCo 2 O 4 with Ti 3 C 2 T x nanosheets generates a number of attractive structural features with strong synergistic effects, such as highly accessible surface areas, intimate 0D/2D interfacial connection, full exposure of abundant active sites, optimized electronic structure, and excellent electron conductivity, all of which are very desirable for the HER process. Consequently, the resulting MnCo 2 O 4 /Ti 3 C 2 T x electrocatalyst possesses an unusual HER ability with a low onset potential of only 51 mV, a small Tafel slope of 79 mV dec −1 and exceptional long-term stability, markedly outperforming the bare MnCo 2 O 4 and Ti 3 C 2 T x electrocatalysts.

Spinel flowered-shaped MnCo2O4 nanocrystals for highly efficient capacitive desalination

• The spinel flower-shaped MnCo 2 O 4 nanocrystals have been synthesized. • The MnCo 2 O 4 possesses abundant redox couples of Mn 2+ /Mn 3+ and Co 2+ /Co 3+ . • The MnCo 2 O 4 cathode has realized high desalination capacity of 88.66 mg/g. In this work, the spinel MnCo 2 O 4 (MCO) nanocrystals have been prepared for high-performance capacitive deionization (CDI). The structure and properties of MCO can be tunneled by varying the annealing temperature from 500 to 700℃.The optimized MCO exhibits the unique flower-shaped structure, which provides abundant channels for ions diffusion. Meanwhile, the diverse valence state related to Mn and Co promotes the adsorption/desorption of Na + . As a result, the desalting capacity of MCO is 88.66 mg g −1 at 1.2 V in 1000 μS cm −1 NaCl solution.

A highly efficient electrocatalyst for oxygen reduction reaction: Spinel MnCo2O4 nanoparticles supported on three-dimensional Nitrogen-doped graphene material with interconnected hierarchical porous nanostructure

• MnCo 2 O 4 /3DNG catalyst was prepared by hydrothermal method using 3DNG as support. • 3DNG with hierarchical porous structure possessed enrich the defects and expose more active sites. • MnCo 2 O 4 /3DNG with hierarchical porous structure contributed to improve mass transfer. • MnCo 2 O 4 /3DNG demonstrated excellent ORR activity and higher durability than 20% Pt/C. We designed and synthesized spinel MnCo 2 O 4 nanoparticles supported on three-dimensional nitrogen-doped graphene (NG) with interconnected hierarchical porous nanostructure, in which polymer (2, 5-benzimidazole) (ABPBI) was used as the nitrogen precursor and the carbon precursor. Unique properties of ABPBI including nitrogen-rich aromaticity and rigid plane molecule were conductive to form NG structures through the pyrolysis dehydrogenative and carbonization. The as-prepared MnCo 2 O 4 -3DNG with interconnected hierarchical porous graphene structure possessed enriched defects and more exposed active sites, accelerating mass transport and facilitating diffusion kinetics for better catalytic ORR performance. MnCo 2 O 4 -3DNG exhibited a higher half-wave potential (0.85 V vs RHE) than 20 wt% Pt/C (0.83 V vs RHE). Moreover, the accelerated durability test and i-t chronoamperometry of MnCo 2 O 4 -3DNG revealed more excellent durability than 20 wt% Pt/C. The electrochemical tests results demonstrated that MnCo 2 O 4 -3DNG was promising as a cost-effective non-noble metal catalyst for ORR in fuel cell technology.

Acid Etching-Induced In Situ Growth of λ-MnO2 over CoMn Spinel for Low-Temperature Volatile Organic Compound Oxidation.

Surface lattice oxygen is crucial to the degradation of volatile organic compounds (VOCs) over transition metal oxides according to the Mars-van Krevelen mechanism. Herein, λ-MnO2 in situ grown on the surface of CoMn spinel was prepared by acid etching of corresponding spinel catalysts (CoMn-Hx-Ty) for VOC oxidation. Experimental and relevant theoretical exploration revealed that acid etching on the CoMn spinel surface could decrease the electron cloud density around the O atom and weaken the adjacent Mn-O bond due to the fracture of the surface Co-O bond, facilitating electron transfer and subsequently the activation of surface lattice oxygen. The obtained CoMn-H1-T1 exhibited an excellent catalytic performance with a 90% acetone conversion at 149 °C, which is 42 °C lower than that of CoMn spinel. Furthermore, the partially maintained spinel structure led to better stability than pure λ-MnO2. In situ diffuse reflectance infrared Fourier transform spectroscopy confirmed a possible degradation pathway where adsorptive acetone converted into formate and acetate species and into CO2, in which the consumption of acetate was identified as the rate-limiting step. This strategy can improve the catalytic performance of metal oxides by activating surface lattice oxygen, to broaden their application in VOC oxidation.

Facet-Defined Strain-Free Spinel Oxide for Oxygen Reduction.

Exposing facet and surface strain are critical factors affecting catalytic performance but unraveling the composition-dependent activity on specific facets under strain-controlled environment is still challenging due to the synthetic difficulties. Herein, we achieved a (001) facet-defined Co-Mn spinel oxide surface with different surface compositions using epitaxial growth on Co3O4 nanocube template. We adopted composition gradient synthesis to relieve the strain layer by layer, minimizing the surface strain effect on catalytic activity. In this system, experimental and calculational analyses of model oxygen reduction reaction (ORR) activity reveals a volcano-like trend with Mn/Co ratios because of an adequate charge transfer from octahedral-Mn to neighboring Co. Co0.5Mn0.5 as an optimized Mn/Co ratio exhibits both outstanding ORR activity (0.894 V vs RHE in 1 M KOH) and stability (2% activity loss against chronoamperometry). By controlling facet and strain, this study provides a well-defined platform for investigating composition-structure-activity relationships in electrocatalytic processes.

A Self-Supported Co-Mn Spinel Electrode for Alkaline Hybrid Zinc Battery with High Charge-Discharge Efficiency of 86%

A Self-Supported Co-Mn Spinel Electrode for Alkaline Hybrid Zinc Battery with High Charge-Discharge Efficiency of 86%

Selective catalytic reduction of NO by Co-Mn based nanocatalysts

Abstract One of the most significant aspects in selective catalytic reduction (SCR) of nitrogen oxides (NOx) is developing suitable catalysts by which the process occurs in a favorable way. At the present work SCR reaction by ammonia (NH3-SCR) was conducted using Co-Mn spinel and its composite with Fe-Mn spinel, as nanocatalysts. The nanocatalysts were fabricated through liquid routes and then their physicochemical properties such as phase composition, degree of agglomeration, particle size distribution, specific surface area and also surface acidic sites have been investigated by X-ray diffraction, Field Emission Scanning Electron Microscope, Energy-dispersive X-ray spectroscopy, energy dispersive spectroscopy mapping, Brunauer–Emmett–Teller, temperature-programmed reduction (H2-TPR) and temperature-programmed desorption of ammonia (NH3-TPD) analysis techniques. The catalytic activity tests in a temperature window of 150–400 °C and gas hourly space velocities of 10,000, 18,000 and 30,000 h−1 revealed that almost in all studied conditions, CoMn2O4/FeMn2O4 nanocomposite exhibited better performance in SCR reaction than CoMn2O4 spinel.

Multifunctional spinel MnCo2O4 based materials for energy storage and conversion: a review on emerging trends, recent developments and future perspectives

In this review, electrocatalysts for HER/OER/ORR and energy storage electrode materials based on MnCo2O4 were reviewed considering their key multifunctional role in the way to a more sustainable society.

A Self-Supported Co-Mn Spinel Electrode for Alkaline Hybrid Zinc Battery with High Charge-Discharge Efficiency of 86%

A Self-Supported Co-Mn Spinel Electrode for Alkaline Hybrid Zinc Battery with High Charge-Discharge Efficiency of 86%

Electrical Resistance of Co-W Alloy Coated Ferritic Stainless Steels As Interconnector Parts of Solid Oxide Fuel Cells

Introduction Over the last decade, several attempts have been made to improve a solid oxide fuel cell (SOFC) system which is one of the most promising alternative power sources due to its high efficiency and low emission. The SOFC system consists of several parts, such as electrolytes, anodes, cathodes, and interconnectors. Recently, the operation temperature of the SOFC system has been reduced to 800 °C, which makes it possible to apply ferritic stainless steels (FSSs) for the interconnector parts. However, the formation of Cr containing oxide layers over time would jeopardize the electrical conductivity of FSS interconnectors. Furthermore, the evaporation of Cr from FSS would react with neighboring components, resulting in their degradation of catalytic activity and electrical conductivity.To overcome these issues, the authors have proposed Co-W alloy electroplating on FSSs. By heat exposure in air, the Co-W coated FSS forms multilayered oxides and among them, a CoWO4 layer effectively suppresses the outward diffusion of Cr cations at high temperatures. However, our former work of the Co-W coated FSSs was conducted under the condition that the coated specimens were separated with other materials, thus for the practical application as interconnector parts, further investigation is required under the simulated condition as a practical SOFC system.In this study, several cathodic half cells were built using the Co-W coated FSSs as interconnector parts and perovskites-type conductive oxides, and the operation condition was simulated by the electricity from a constant current power source. For the cathode materials, La0.8Sr0.2MnO2.97 (LSM) and La0.8Sr0.2Co0.8Fe0.2O2.97 (LSCF) were selected due to their high electrical conductivity and high reaction activity. The results of their electrical performance and microstructural changes of the half cells are discussed. Results and discussions The cross-sections of uncoated and Co-W coated LSM specimens after 500 h exposure in air at 800 °C are shown in the following image. The formation of a CoWO4 oxide layer brought a significant influence on the Cr outward diffusion.In the uncoated samples, Cr diffuses into both LSM and LSCF specimens to form Cr containing particulate oxides such as SrCrO4 or MnCr2O4, showing the Cr-poisoning. Further, the Cr oxide layer was not continuous in the uncoated samples due to Cr evaporation. Thus, internal oxidation in the grain boundaries are observed by the BSE image.On the other hand, the Co-W coated samples exhibited in a completely different manner. Similar to our previous study, after oxidation, the five-layered structure was formed beneath the LSM and LSCF coatings. In the five layered oxides, Cr is enriched just beneath the Co-W oxide layer to form a continuous and dense Cr oxide layer. Thus, the further oxidation of the substrate is suppressed by the presence of the CoWO4 layer, due to its role as an outward diffusion blocker of Cr which accordingly protects cathodic materials against Cr poisoning. In addition, the ASR measurement proved that the addition of W in the Co coating does not significantly increase the electrical resistance of the cathodic system compared with those of other Co based coatings.It should also be noted that the LSM particles showed an intrusion effect into the oxide layer formed on the metallic surface. Co oxide reacts with Mn oxide in the LSM cathode layer to form a Co-Mn spinel which can improve the adherence between the cathode and the protective layer. This intrusion effect can also reduce the contact resistance and improve the electrical property. And this kind of Mn-Co spinels are typically used in the SOFC interconnects for their good CTE mismatch with the substrate stainless steel and high electric conductivity. Conclusions For the evaluation of Co-W alloy electroplated ferritic stainless steels, cathodic half cells were fabricated simulating the SOFC system, and the following conclusions are drawn. The CoWO4 layer effectively suppressed the outward diffusion of Cr and protected cathode materials against Cr poisoning.The ASR value by the Co-W coated specimens were almost comparative to those in Co-based alloy coatings, confirming that W addition did not significantly increase the ASR values.LSM particles showed an intrusion effect into the oxide layer formed on the metallic surface. Co oxide reacts with Mn oxide in the LSM cathode layer to form a Co-Mn spinel which can improve the adherence between the cathode and the protective layer. Figure 1

Mn-O Covalency Governs the Intrinsic Activity of Co-Mn Spinel Oxides for Boosted Peroxymonosulfate Activation.

Transition metal (TM)-based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot fully explain the efficient TM redox cycling. Here, we discover a critical role of TM-O covalency in governing the intrinsic catalytic activity of Co3-x Mnx O4 spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn-O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor MnOh -PMS interaction. With appropriate MnIV /MnIII ratio to balance PMS adsorption and MnIV reduction, the Co1.1 Mn1.9 O4 exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts.

Insight into an invisible active site presented in the low temperature pyrolysis of toluene by CoMn spinel catalyst

In this work, CoMn spinel (MnCo2O4+δ) was prepared from CoMn LDH and was applied as a catalyst toward toluene pyrolysis. Spinel samples with different degrees of crystallinity were evaluated by isothermal and stepwise heating experiments, as well as feeding toluene with different concentrations. Especially for the spinel with high degree of crystallinity, results exhibited a relatively low pyrolysis temperature of 400 °C, a high toluene conversion rate of ~ 100%, a large H2 production and an acceptable benzene formation. More importantly, by various characterization techniques, an invisible active site was detected and believed to be formed by the reaction of CoMn spinel with toluene, and was designated as manganosite-cobalt nanoparticles supported on carbon nanotubes (MnO-Co/CNTs), which significantly promoted the degradation and carbonization reactions in the low temperature pyrolysis of toluene.