Mn-Co Oxide Research Articles

Structure dependence of the enhanced sulfur tolerance of core–shell CoMn oxides for benzene oxidation: Discrepant sulfur species and less affected reactant activation

Effective reduction of VOCs emissions in practical gas requires low-temperature catalysts with remarkable SO2 tolerance. Here via simply mixing CoCO3 into the precursors of α-MnO2, a core–shell CoMn composite was developed. The leading one with CoCO3 addition of 3 g (Co3Mn) achieved 100 % C6H6-to-CO2 conversion at ≥250 °C under 120 L/g/h, and still the CO2 yield over the sulfurized Co3Mn (simulated by H2SO3 vapor pretreatment) was maintained 100 %. However, with respect to the case of fresh MnO2, the CO2 production at 250 and 300 °C over the sulfurized MnO2 was decreased by 26 % and 8 %, respectively, and in the meantime, a larger amount of CO was detected. The dominant formation of abundant MnSO4 species due to sulfur poisoning led to the deactivation of pure MnO2, while over Co3Mn the formation of MnSO4 was significantly inhibited because of (i) the electron transfer from Co2+ to Mn4+ restraining that from S4+ to Mn4+ and (ii) the stronger alkalinity of Co species making the acidic H2SO3 preferentially anchor on Co as CoSO4. Along with the sacrificial role, another way cobalt alleviated sulfate toxicity was through transiting the aggregated sulfate deposition into scattered state. Investigations conducted primarily with UV–vis DRS and temperature-programmed techniques further reveal that neither MnO2 nor Co3Mn could escape from the sulfur-induced adversity on activation of O2 and benzene, but the sulfurized Co3Mn was much less affected, thus sustaining the deep benzene oxidation. Finally, reaction routes were unraveled according to the phenol, benzoquinone, maleic acid and acetic acid intermediates.

Strong water-resistant Co-Mn solid solution derived from bimetallic metal–organic frameworks for catalytic destruction of toluene

The construction of Co-Mn mixed metal oxides catalysts derived from bimetallic MOFs has great significance for catalytic destruction of toluene. Hence, a series of CoaMnbOx-MOFs with different physicochemical properties were successfully synthesized via pyrolysis of Co-Mn bimetallic MOFs. Attributing to the higher specific surface area, more active sites (Co3+ and Mn3+), stronger reducibility and abundant defect sites, the as-prepared Co1Mn1Ox-MOFs dispalyed an optimal catalytic performance, especially the excellent water vapor resistance. The result of the In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy demonstrated that toluene can be degraded at relatively low temperatures (＜100 °C). Benzyl alcohol, benzaldehyde, benzoic acid and maleic anhydride were the main intermediate products in toluene degradation process. This work reveals the value of bimetallic MOFs derived Co-Mn oxides for toluene oxidation and presents a novel avenue for designing mixed metal oxide catalysts with potential applications in VOCs catalytic oxidation.

Facile construction and enhanced catalytic activity of Co-Mn oxide with rich amorphous/crystalline interfaces for propane oxidation

Cobalt-manganese (Co-Mn) composite oxides show high potential for the catalytic oxidation of volatile organic compounds (VOCs). However, the low defect content and poor oxygen mobility of perfect spinel structure crystalline always make it difficult to effectively activate C–H bonds of propane. Here, the catalyst with rich amorphous MnOx/crystalline Co3O4 interfaces was prepared, and the catalytic combustion activity for propane was determined. The rich amorphous/crystalline interfaces CMO-400 (i.e. Co-Mn oxide calcined at 400 °C) catalyst exhibited the best catalytic activity for propane with T90 of 200 °C among all bimetallic Co-Mn oxides. Various characterizations and corresponding results have demonstrated that the abundant amorphous/crystalline interfaces could improve the catalytic performances, attributed to high oxygen vacancy concentration, low temperature reducibility, weak Mn−O bond strength, and good surface lattice oxygen mobility. It is noteworthy that the interface engineering of amorphous/crystalline is an effective strategy in VOCs catalytic oxidation.

Oxygen-enriched vacancy spinel Mn-Co oxides by deep thermal reduction for enhanced antibiotics degradation efficiency

In this research work, flower-like MnCo2O4.5 was synthesized by introducing a short-chain surfactant as a surface-active agent. This structure was utilized as a precursor, and a gas atmosphere pyrolytic deep reduction strategy was employed to construct a sea urchin-like catalyst (DTR-Vo-MCO) with abundant oxygen vacancies. A series of characterizations were conducted to reveal the catalyst's microstructure and crystal phase composition. DTR-Vo-MCO achieved more than 90% degradation of OTC within 10 min, and the efficiency was 1.5 times that of Vp-MCO. The substantial presence of oxygen defects on the DTR-Vo-MCO surface expedited charge transfer processes, resulting in a remarkable enhancement of PMS activation efficiency. Electron paramagnetic resonance spectroscopy (EPR) and radical quenching experiments indicated that the contributions of radicals to oxytetracycline (OTC) degradation were in the order of 1O2 > SO4•– > O2•– > •OH. 1O2 and SO4•– played dominant roles in OTC degradation. The possible oxytetracycline degradation pathways were proposed based on LC-MS analysis. In summary, this work presents an efficient method for a highly oxygen-deficient catalyst, expanding the application of binary transition metal materials in environmental remediation.

Gd-modified Mn-Co oxides derived from layered double hydroxides for improved catalytic activity and H2O/SO2 tolerance in NH3-SCR of NOx reaction

Metal oxides derived from layered double hydroxides (LDHs) are expected to obtain low-temperature denitrification (de-NOx) catalysts with high catalytic activity and H2O/SO2 tolerance in the selective catalytic reduction (SCR) of NOx with NH3. In current work, we successfully prepared Gd-modified Mn-Co metal oxides derived from Gd-modified Mn-Co LDHs. The resultant Gd-modified Mn-Co metal oxides exhibit excellent catalytic activity and high H2O/SO2 tolerance in the NH3-SCR de-NOx reaction. The reasons for the enhancement can be ascribed to the unique surface physicochemical properties inherited from LDHs and the modification of Gd, which increase the specific surface area, improve the relative content of Mn4+ and Co3+ on the surface, enhance the number of acidic sites, strengthen the reducibility of catalyst, resulting in the enhanced catalytic activity and H2O/SO2 tolerance. Additionally, it is demonstrated that the NH3-SCR de-NOx reaction occurred on the surface of Gd-modified Mn-Co oxides followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. This study provides us with a design approach to promote catalytic activity and H2O/SO2 tolerance through morphology control and rare earth modification.

Anodic and Cathodic preparation of MnO2/Co2O3 Composite Electrode Anodes for Electro-Oxidation of Phenol

The economical and highly performed anode material is the critical factor affecting the efficiency of electro-oxidation toward organics. The present study aimed to detect the best conditions to prepare Mn-Co oxide composite anode for the electro-oxidation of phenol. Deposition of Mn-Co oxide onto graphite substrate was investigated at 25, 30, and 35 mA/cm2 to detect the best conditions for deposition. The structure and the crystal size of the Mn-Co oxide composite electrode were examined by using an X-Ray diffractometer (XRD), the morphological properties of the prepared electrode were studied by scanning electron microscopy (SEM) and Atomic force microscopy (AFM) techniques, and the chemical composition of the various deposited oxide was characterized by energy dispersive X-ray spectroscopy (EDX). The study also highlighted the effect of current density (40, 60, and 80 mA/cm2), pH (3, 4, and 5), and the concentration of NaCl (1, 1.5, and 2 g/l) on the anodic electro-oxidation of phenol was investigated. The results revealed that the composite anodes are successfully prepared galvanostatically by anodic and cathodic deposition. In addition, the current density of 25 mA/cm2 gave the best cathodic deposition performance. The removal efficiency of phenol and other by-products increased as the current density and the concentration of NaCl in the electrolyte increased, while it decreased as the pH increased. The prepared composite electrode gave high COD removal efficiency (98.769 %) at the current density of 80 mA/cm2, pH= 3, NaCl conc. of 2 g/L within 3 h.

General Route to Colloidally Stable, Low-Dispersity Manganese-Based Ternary Spinel Oxide Nanocrystals.

While certain ternary spinel oxides have been well-explored with colloidal nanochemistry, notably the ferrite spinel family, ternary manganese (Mn)-based spinel oxides have not been tamed. A key composition is cobalt (Co)-Mn oxide (CMO) spinel, CoxMn3-xO4, that, despite exemplary performance in multiple electrochemical applications, has few reports in the colloidal literature. Of these reports, most show aggregated and polydisperse products. Here, we describe a synthetic method for small, colloidally stable CMO spinel nanocrystals with tunable composition and low dispersity. By reacting 2+ metal-acetylacetonate (M(acac)2) precursors in an amine solvent under an oxidizing environment, we developed a pathway that avoids the highly reducing conditions of typical colloidal synthesis reactions; these reducing conditions typically push the system toward a monoxide impurity phase. Through surface chemistry studies, we identify organic byproducts and their formation mechanism, enabling us to engineer the surface and obtain colloidally stable nanocrystals with low organic loading. We report a CMO/carbon composite with low organic contents that performs the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.87 V vs RHE in 1.0 M potassium hydroxide at 1600 rpm, rivaling previous reports for the highest activity of this material in ORR electrocatalysis. We extend the general applicability of this procedure to other Mn-based spinel nanocrystals such as Zn-Mn-O, Fe-Mn-O, Ni-Mn-O, and Cu-Mn-O. Finally, we show the scalability of this method by producing inorganic nanocrystals at the gram scale.

Identifying the in situ protection role of MnO2 nanosheets on Co oxide for superior water oxidation

As a limiting step of electrochemical water splitting, the oxygen evolution reaction calls for efficient catalysts to surmount the high energy barrier. In this work, the synthesis of O-deficient Co3O4 nanoparticles with abundant surface area was realized by applying two-dimensional MnO2 nanosheets as a self-protection agent. The strong interaction between Mn and Co was confirmed by our experiments and DFT calculations that the valence state is increased for Co while it is reduced for Mn during the annealing in reducing atmosphere. Mn3+δ with stronger Lewis acidity can protect Co2+ from being reduced when subjected to the H2 treatment. The H2– reduced CoMn oxide under 300 °C (CMO-H300) shows the best OER activity with an overpotential of 280 mV in 1 M KOH and 460 mV in 1 M phosphate buffer (PBS) at 10 mA cm-2 geo, which can be attributed to the optimal chemical state, appropriate oxygen vacancies and highly exposed surface area. Operando Raman spectroscopy combined with ex-situ XPS revealed the manner of active species evolution in CMO-FD (Freezing-drying CoMn oxide) and CMO-H300 under the OER process, which accounted for the dynamic change of chronoamperometry. Our findings provide a different viewpoint for novel electrocatalyst fabrication by introducing a self-sacrifice agent that in situ promotes electronic structure modulation and high surface area preservation.

Dynamics of Co/Co2C redox cycle and their catalytic consequences in Fischer–Tropsch synthesis on cobalt–manganese catalysts

Fischer–Tropsch synthesis over CoMn oxides is a surface-catalyzed structure-sensitive reaction. Active site changes greatly alter product distribution. The dynamics and essence of the changes in Co species during the reaction have seldom been explored. Herein, multiple characterizations were applied to confirm that two types of active sites, i.e., Co and Co2C, coexist on CoMnOx under the reaction conditions. Apart from the direct participation of carbon species in the reaction, the steady-state isotopic transient kinetic analysis also suggested the mutual transformation of carbon species in Co2C. The ratio of the two paths altered with the temperature, thus leading to Co2C-rich and Co-rich surfaces at intermediate and high temperatures, respectively. Kinetic calculations and microkinetic modeling showed that Co2C-rich surfaces facilitated CO adsorption and suppressed hydrogen adsorption. This gave high carbon-chain growth activity. The Co-rich surfaces showed high vacancy and hydrogen coverages, lowering the CO activation and CH4 formation energies.

Facile synthesis of Schistose-like Co-Mn oxides for low-temperature catalytic oxidation of NO with enhanced SO2/H2O tolerance

The schistose-like Mn-Co oxides were synthesized by thermal decomposition of inorganic salts as catalyst for NO oxidation. The morphological and surface structural properties can be efficiently regulated by controlling the ratio of Co/Mn. Schistose-layered structure with plentiful nanopores not only facilitates the exposure of active sites but also improves the diffusion and adsorption of NO. Abundant active oxygen species and highly content of Mn4+ formed on the surface of Co1Mn4 play a vital role in the catalytic oxidation of NO. Thus, Co1Mn4 catalyst achieves the highest conversion rate of 54.4 % at 120 °C and 91.3 % at 240 °C. Moreover, satisfactory long-time stability as well as outstanding tolerance to SO2 and H2O could be obtained for Co1Mn4 catalyst. Distinct distinctions on the variation of nitrate/nitrite species over Mn and Co1Mn4 are discovered by in-situ DRIFTS, which provided basis for elucidating the reaction mechanism. This work broadens the horizons for the design of bimetallic catalysts for low-temperature NO oxidation.

Stabilization of a Mn-Co Oxide During Oxygen Evolution in Alkaline Media.

Improving the stability of electrocatalysts for the oxygen evolution reaction (OER) through materials design has received less attention than improving their catalytic activity. We explored the effects of Mn addition to a cobalt oxide for stabilizing the catalyst by comparing single phase CoOx and (Co0.7Mn0.3)Ox films electrodeposited in alkaline solution. The obtained disordered films were classified as layered oxides using X‐ray absorption spectroscopy (XAS). The CoOx films showed a constant decrease in the catalytic activity during cycling, confirmed by oxygen detection, while that of (Co0.7Mn0.3)Ox remained constant within error as measured by electrochemical metrics. These trends were rationalized based on XAS analysis of the metal oxidation states, which were Co2.7+ and Mn3.7+ in the bulk and similar near the surface of (Co0.7Mn0.3)Ox, before and after cycling. Thus, Mn in (Co0.7Mn0.3)Ox successfully stabilized the bulk catalyst material and its surface activity during OER cycling. The development of stabilization approaches is essential to extend the durability of OER catalysts.

Investigation of Sulfur Doping in Mn-Co Oxide Nanotubes on Surface-Enhanced Raman Scattering Properties.

Doping engineering is an efficient strategy to manipulate the optoelectronic properties of metal oxides for sensing, catalysis, and energy applications. Herein, we have demonstrated the fabrication of sulfur (S)-doped Mn-Co oxides to regulate their band and surface electronic structures, which is beneficial to enhancing the charge transfer (CT) between the metal oxides and their adsorbed molecules. As expected, significantly enhanced SERS signals are achieved on S-doped Mn-Co oxide nanotubes, and the minimum detection concentration can reach as low as 10-8 M. Furthermore, the change in the electronic structure caused by S-doping provides different microelectric fields to influence the orientation of the interaction between the probe molecules and the substrate. Additionally, the evaluation of the oxidase-like catalytic activity of the substrate proved that, with an increase in the ratio of Co2+/Co3+ content, the number of electrons on the substrate increases, which promotes the CT process and further increases the degree of CT. The nonmetallic doping route in semiconducting metal oxides can provide effective and stable SERS activity; moreover, it provides a new strategy for exploring the relationship between CT in catalysis and SERS performance of semiconductors.

Hydrothermal synthesis of nanocages of Mn-Co Prussian blue analogue and charge storage investigation of the derived Mn-Co oxide@/rGO composites

Prussian blue analogues (PBA) and their derived materials are intriguing for energy storage platforms due to the intrinsic open framework, tunable composition, low cost, and easy preparation. In recent years, current research has focused on improving their conductivity and energy storage. In this paper, cobalt-manganese Prussian blue analogues (PBA) were hydrothermally synthesized as self-assembly on graphene oxide. The obtained intermediate was precisely heat-treated to produce Co-Mn oxide nanocages on reduced graphene oxide (Mn-Co oxide/rGO). The as-prepared composite was characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectrometry (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDX), Raman Spectroscopy, transmission electron microscopy (TEM), Thermogravimetric analyzer (TGA), and Brunauer-Emmett-Teller (BET) surface area analysis. It had been discovered that the interaction between the carbon and the Co-Mn Oxide not only prevents the agglomeration and significantly maximizes the surface, but also provides a network of conductive surface for quick electron transport resulting in an effective electrical transmission path and improved ionic absorbability and conductivity. The Mn-Co oxide @rGO nanocomposite delivers a maximum specific capacitance of 809 Cg−1 in 3 M KOH aqueous electrolyte at a high current density of 1 A g−1. After 4000 cycles at 20 A g−1 current density, the nanocomposite had preserved 86% of its starting capacitance. A two-electrode asymmetric cell (ASC) was designed and tested for electrochemical performance using Mn-Co oxide @ rGO as the positive electrode and activated carbon (AC) as the negative electrode. The designed device works excellently, with a maximum energy and power density of 55.55 Wh kg−1 and 972.73 W kg−1 in 1 A g−1, respectively.

Excellent performance and outstanding resistance to SO2 and H2O for formaldehyde abatement over CoMn oxides boosted dual-precursor hierarchical porous biochars derived from liquidambar and orange peel

This study supplies a facile strategy to design novel carbon-based catalysts with hierarchical porous carrier for the efficient removal of HCHO. A series of CoMn oxides boosted hierarchical porous biochars (CoMn/HPBs) derived from liquidambar and orange peel were synthesized for HCHO removal. The physicochemical properties and removal mechanism of above-mentioned samples were evaluated by means of BET, XRD, SEM, EDX, H2-TPR, XPS and in situ DRIFTS. 12%Co0.33Mn0.67/HPB exhibited delightful EHCHO, favorable thermal stability and excellent resistance to SO2 and H2O in a wide temperature window from 140 to 360 °C. The inhibitory influences of SO2 and H2O could defeat the promotional effect of O2 by a narrow margin. Co and Mn co-modified HPB exhibited better performance than that of Co or Mn individually modified HPB, which was attributed to the redox cycle of Mn4+/Mn3++Co2+↔Mn3+/Mn2++Co3+ and the synergistic effect between CoOx and MnOx, resulting in more active oxygen vacancies, higher redox ability and better dispersion of metal oxides. Besides, the hierarchical porous structure of support not only furnished abundant surface functional groups, but also facilitated the accessibility of adsorption/catalytic active sites and boosted the convenient mass transfer of reactants and products. Therefore, these superior properties contributed to boosting the catalytic performance, enhancing the thermal stability and perfecting the resistance to SO2 and H2O. Moreover, both adsorption and catalytic oxidation worked together for HCHO removal over 12%Co0.33Mn0.67/HPB. Meanwhile, catalytic oxidation predominated gently with the augmentation of reaction temperature and time.

Multi-Centered Solid-Phase Quasi-Intramolecular Redox Reactions of [(Chlorido)Pentaamminecobalt(III)] Permanganate—An Easy Route to Prepare Phase Pure CoMn2O4 Spinel

We synthesized and structurally characterized the previously unknown [Co(NH3)5Cl](MnO4)2 complex as the precursor of CoMn2O4. The complex was also deuterated, and its FT-IR, far-IR, low-temperature Raman and UV-VIS spectra were measured as well. The structure of the complex was solved by single-crystal X-ray diffraction and the 3D-hydrogen bonds were evaluated. The N-H…O-Mn hydrogen bonds act as redox centers to initiate a solid-phase quasi-intramolecular redox reaction even at 120 °C involving the Co(III) centers. The product is an amorphous material, which transforms into [Co(NH3)5Cl]Cl2, NH4NO3, and a todorokite-like solid Co-Mn oxide on treatment with water. The insoluble residue may contain {Mn4IIIMnIV2O12}n4n−, {Mn5IIIMnIVO12}n5n− or {MnIII6O12}n6n− frameworks, which can embed 2 × n (CoII and/or CoIII) cations in their tunnels, respectively, and 4 × n ammonia ligands are coordinated to the cobalt cations. The decomposition intermediates decompose on further heating via a series of redox reactions, forming a solid CoIIMIII2O4 spinel with an average size of 16.8 nm, and gaseous N2, N2O and Cl2. The CoMn2O4 prepared in this reaction has photocatalytic activity in Congo red degradation with UV light. Its activity strongly depends on the synthesis conditions, e.g., Congo red was degraded 9 and 13 times faster in the presence of CoMn2O4 prepared at 550 °C (in air) or 420 °C (under N2), respectively.

Effects of alkaline-earth metals on CoMn-based catalysts for the Fischer–Tropsch synthesis to olefins

Alkaline-earth metal promoted CoMn catalysts with higher surface basicity benefit the carburization of CoMn oxides to form more Co2C nanoprisms for olefin formation, especially for long-chain olefins.

Ce-induced regulation of electron density enhanced the catalytic activity of Co-Mn oxides for water oxidation.

The incorporation of Ce into Co-Mn oxides induced the charge redistribution of Co and Mn via electronic coupling, which facilitated the Co3+/Co4+ transition. Thus, the overpotential at 10 mA cm-2 was reduced significantly by 73 mV for the oxygen evolution reaction after Ce doping.

Activation of peroxymonosulfate by bimetallic CoMn oxides loaded on coal fly ash-derived SBA-15 for efficient degradation of Rhodamine B

• Mesoporous SBA-15 is successfully synthesized with coal fly ash as the silicon source. • CoMn/SBA-15 exhibits excellent performance for RhB degradation by activating PMS. • Synergistic effects of Co and Mn species are inferred. • Non-radical ( 1 O 2 ) rather than radicals (SO 4 − and OH) contributes most to the degradation. • Mechanisms of PMS activation and the degradation pathways of RhB are proposed. In this study, we successfully synthesized SBA-15 mesoporous molecular sieve with coal fly ash (CFA) as the silicon source, fabricated bimetallic CoMn catalysts with the obtained SBA-15 as the support, and evaluated their performance for activating peroxymonosulfate (PMS) to degrade the Rhodamine B (RhB) in an aqueous solution. The characterization results signified that MnCo 2 O 4 spinel was formed and uniformly dispersed on SBA-15 for the as-prepared CoMn/SBA-15. The CoMn/SBA-15/PMS system exhibited markedly higher RhB removal efficiency compared with Co/SBA-15/PMS and Mn/SBA-15/PMS under the same reaction conditions. Moreover, bimetallic CoMn/SBA-15 presented much lighter metal leaching than the monometallic catalysts. Chemical quenching tests and electron paramagnetic resonance experiments ascertained the generation of free radicals (SO 4 − and OH) and non-radical (singlet oxygen, 1 O 2 ) reactive oxygen species by PMS activation and the dominant role 1 O 2 in RhB degradation. The formed intermediate products by RhB degradation were identified with LC-MS analyses. We have also performed LC-MS analyses to determine the formed intermediate products during RhB degradation. The present results demonstrate the pronounced potential of CFA as a silicon source of molecular sieve support for preparing various heterogeneous catalysts for the PMS-based oxidation of organic pollutants in wastewater.

In Situ Study of Reduction of MnxCo3-xO4 Mixed Oxides: The Role of Manganese Content.

A series of Mn-Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37-63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn-Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn-Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co)3O4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co)3O4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

Accelerating Aging Test on Solid Oxide Cell Interconnects

The degradation of metal interconnects (ICs) is one of the main lifetime limiting issues in Solid Oxide Cells (SOCs). Chromium oxide thermally grows on the substrate surface that causes ohmic loss and its vapors poison the oxygen electrode reaction (OER). Mn-based spinels are presently among the materials of choice to protect ICs to prevent Cr diffusion.As the target lifetime is around 40000h, it is of interest to design accelerated ageing tests, under harsher than nominal operating conditions, to simulate the long-time ageing behavior at nominal conditions.In this study, the performance of IC coatings was investigated with accelerated ex-situ corrosion ageing tests, in which the operating condition of the air-side interconnect was simulated. Temperature and humidity were selected as test variable parameters. Area Specific Resistance (ASR) and Cr depletion/migration were studied for the stressed conditions. Tests were carried out on stainless steel substrate with Mn-Cu-Oxide and Mn-Co-Oxide as protective coatings.Ageing tests over 1000h at different temperatures (750-950°C) and humidity (above 15%RH) were run while monitoring the ASR of the samples. Fig. 1 shows the ASR results for the samples run at different temperatures and in dry condition. Based on Fig. 1a-e, it is observed that the ASR trends remain constant during the test time. Although 916°C is well above nominal operating temperature, the ASR showed constant value within a reasonable range. At a test temperature 950°C (Fig. 1f), the ASR behavior of samples containing Co-Mn Oxide protective coating is the same found for lower temperatures; however, a sharp ASR increase in Mn-Cu Oxide coated samples can be observed. Applying humidity to high-temperature conditions also may help to accelerate the test, and its results will be presented. SEM/EDX post-test characterization provides information on the scale morphology and helps to understand the different behaviors at different stressed conditions.Keywords: SOC; interconnect; protective coating; ageing test; accelerating test; Cr diffusion; ASR; Figure 1