Oxidation State Of Co Research Articles

Operando XANES Reveals the Chemical State of Iron-Oxide Monolayers During Low-Temperature CO Oxidation.

We have used grazing incidence X-ray absorption near edge spectroscopy (XANES) to investigate the behavior of monolayer FeOxfilms on Pt(111) under near ambient pressure CO oxidation conditions with a total gas pressure of 1 bar. Spectra indicate reversible changes during oxidation and reduction by O2 and CO at 150ºC, attributed to a transformation between FeO bilayer and FeO2 trilayer phases. The trilayer phase is also reduced upon heating in CO+O2, consistent with a Mars-van-Krevelen type mechanism for CO oxidation. At higher temperatures, the monolayer film dewets the surface, resulting in a loss of the observed reducibility. A similar iron oxide film prepared on Au(111) shows little sign of reduction or oxidation under the same conditions. The results highlight the unique properties of monolayer FeO and the importance of the Pt support in this reaction. The study furthermore demonstrates the power of grazing-incidence XAFS for in situ studies of these model catalysts under realistic conditions.

Insights into the Construction of Robust Pt Clusters with Satisfactory Stability on CeO2 for the Catalytic Oxidation of CO.

Improving the efficiency of platinum group metals (Pt, Pd, Rh, etc.) in catalytic oxidation reactions remains an urgent topic. The conflict between the low-temperature activity and high-temperature stability of noble metals can hardly reach a consensus. For instance, Pt cluster catalysts supported on CeO2 with high low-temperature activity will suffer from deactivation due to the redispersion under high-temperature lean-burn reaction conditions. Herein, two Pt1/CeO2 prepared by the incipient wetness impregnation method using different Pt precursors possessed varied Pt-O and Pt-O-Ce coordination numbers (CNs). They showed various priorities in CO oxidation versus NH3 selective catalytic oxidation, materials with higher CNPt-O-Ce selectively catalyzing NH3 oxidation to N2 more superior, conversely materials with lower CNPt-O-Ce performing better in CO oxidation. After activation by H2 reduction, both formed massive Pt clusters on the CeO2 surface but showed drastically distinct stability in lean-burn CO oxidation reactions. By summarizing the experimental results of high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, Raman spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, etc., it is beyond doubt that the difference in the initial states of Pt1 due to distinct precursors indeed determine the redispersion behavior of the reduced Pt clusters on CeO2. Materials with lower CNPt-O-Ce and higher CNPt-O are more likely to form robust Pt clusters, as they are not conducive to Pt anchoring, thus restricting the reversible structural evolution occurring under lean-burn CO oxidation and reductive conditions. This approach serves as a guide for the convenient and efficient construction and exploration of robust Pt cluster catalysts.

Modulating effect of urea/melamine on Co2+/Co3+ ratio of Co3O4 microplates for rapid hydrogen generation via NaBH4 hydrolysis

The oxidation state of an active metal is vital in the hydrolysis of NaBH4 for rapid hydrogen generation since the electron-rich and electron-deficient sites facilitate BH4− and H2O adsorption. Herein, we systematically design a tunable oxidation state of Co in Co3O4 by in situ N-doing using the combination of melamine (M) and urea (U) as nitrogen precursors during thermal treatment. The oxidation state of Co was tuned via electronic interaction between N and Co. This interaction was optimized by varying the amount of N doping and calcination temperature. The types of heterocyclic nitrogen, mainly pyridinic- and graphitic-N, and their carbon matrix content are critical in controlling the Co oxidation state. Various Co2+/Co3+ ratios showed a different catalytic performance, and the catalytic activity reached its peak at the highest ratio of 2.74 due to the synergetic effect of the maximum adsorption of BH4− and H2O by Co2+ and Co3+, respectively. Consequently, an excellent hydrogen generation rate (2042 mL g−1 min−1) was achieved with a low activation energy of 46.9 kJ mol−1 of M2.5U10Co3O4-400. Hence, N doping from a dual N source significantly enhanced the hydrogen performance compared to the reported cobalt-based catalyst. Furthermore, M2.5U10Co3O4-400 is highly recyclable, implying its stability and practical application.

Gold oxide formation on Au(111) under CO oxidation conditions at room temperature.

Although gold-based catalysts are promising candidates for selective low-temperature CO oxidation, the reaction mechanism is not fully understood. On a Au(111) model catalyst, we observe the formation of gold oxide islands under exposure to atmospheric pressures of oxygen or CO oxidation reaction conditions in an in situ scanning tunneling microscope. The gold oxide formation is interpreted in line with the water-enabled dissociation of O2 on the step edges of Au(111). Contaminants on the gold surface can strongly promote the gold oxide formation even on the terraces. On the other hand, TiO2 nanoparticles on the Au(111) do not show any influence on the formation of the gold oxide and are thus not providing a significant amount of atomic oxygen to the gold at room temperature. Overall, the presence of gold oxide is likely under industrial conditions.

Morphology-electronic effects in ultra-model nanocatalysts under the CO oxidation reaction: the case of ZnO ultrathin films grown on Pt(111).

The study of the surface morphology and interface of metal-oxides is crucial for understanding the behavior of these model systems as nanocatalysts. Besides, understanding the interplay between morphology, stability, and reactivity is crucial for designing efficient catalysts. Here, we investigated the stability and dewetting of ZnO ultrathin films on Pt(111) under CO oxidation conditions. For films <1 monolayer (ML), CO-induced dewetting occurs at the metal-oxide interface or defects. The morphology, dependent on thickness, influences reactivity. (6 × 6) structures show greater CO binding and structural changes compared to (4 × 4) structures, which exhibit resilience due to Zn-OH formation. ZnO electronic properties, as revealed by Auger spectroscopy and scanning tunneling spectroscopy (STS) investigations, vary with thickness. Low-thickness films [<2 monolayers (ML)] exhibit metallic-like behavior, possibly due to Zn-Pt interaction, while thicker films show n-type semiconductor behavior with a bandgap opening (EBG = 0.9 eV at 2 ML). DFT calculations of the local density of states (LDOS) as a function of ZnO thickness confirm the thickness-dependent electronic structure, with 0.3 ML films having a higher LDOS near the Fermi level than 1 ML films. These findings highlight the critical role of ZnO morphology in determining its stability and reactivity which opens up avenues for designing efficient and more stable ZnO-based nanocatalysts for a wide range of chemical reactions, including CO oxidation and CO2 hydrogenation.

Enhancing oxygen evolution functionality through anodization and nitridation of compositionally complex alloy

Compositionally complex materials (CCMs) have recently attracted great interest in electrocatalytic applications. To date, very few materials were systematically developed and tested due to the highly difficult preparation of high-surface-area CCMs. In this work, a surface of a compositionally complex FeCoNiCuZn alloy (CCA) was nitridated with subsequent anodization leading to morphological and compositional modifications. Notably, the electrochemical surface area and surface roughness as well as the electrocatalytic activity of the anodized material exhibit significant enhancement. Oxygen evolution reaction (OER) activity by the anodized CCN (CCN–AO) proceeds with remarkably small overpotential (233 mV) at 10 mA cm−2 in 1 M KOH. Experimental characterization indicates that the oxidation state of Co plays a critical role in the Fe–Co–Ni electrocatalyst. The developed approach and design strategy open up immense prospects in the preparation of a new, affordable, scalable and effective type of complex and high-performance electrocatalytic electrodes with tunable properties.

Promotional effect of stannum on Pd/CeO2 catalysts for CO and C3H6 co-oxidation

The successful control of hydrocarbon and CO emissions from low-temperature diesel exhausts requires the use of highly active co-oxidation catalysts. In this study, Sn was used to enhance the catalytic performance of Pd/CeO2 in CO and C3H6 co-oxidation conditions. CeO2 with added stannum (Sn) was prepared as a support using the co-precipitation method, and Pd was loaded onto the support using the impregnation method. After Sn addition (the optimal Ce/Sn ratio is 0.75:0.25), the T50 values of CO and C3H6 are reduced by 20 and 32 °C, respectively. A series of characterization methods indicates that the addition of Sn to the support greatly enhances its lattice oxygen mobility and increases the proportion of PdO. During the co-oxidation process, stronger lattice oxygen mobility allows CO to react faster through the Mars–van Krevelen mechanism, weakening the competition with C3H6 for O2. A higher PdO content enhances the C3H6 oxidation capability. Moreover, CO can more readily reduce PdO than Pd2+ in solid solution with the support, which consequently further enhances co-oxidation activity. Therefore, the addition of Sn is a simple and effective strategy for enhancing the performance of Pd/CeO2 catalysts in CO and C3H6 co-oxidation reactions. Furthermore, the promotional effect of CO achieved in this study contributes to a deeper understanding of the interactions that occur during the co-oxidation of C3H6 and CO.

Unveiling the Electrolyte Cations Dependent Kinetics on CoOOH-Catalyzed Oxygen Evolution Reaction.

The electrolyte cations-dependent kinetics have been widely observed in many fields of electrocatalysis, however, the exact mechanism of the influence on catalytic performance is still a controversial topic of considerable discussion. Herein, combined with operando X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), we verify that the electrolyte cations could intercalate into the layer of pristine CoOOH catalyst during the oxygen evolution reaction (OER) process, while the bigger cations lead to enlarged interlayer spacing and increased OER activity, following the order Cs+ >K+ >Na+ >Li+ . X-ray absorption spectroscopy (XAS), in situ Raman, in situ Ultraviolet-visible (UV/Vis) spectroscopy, in situ XAS spectroscopy, cyclic voltammetry (CV), and theoretical calculations reveal that the intercalation of electrolyte cations efficiently modify the oxidation states of Co by enlarging the Co-O bonds, which in turn enhance the d-band center of Co, optimize the adsorption strength of oxygen intermediates, facilitate the formation of OER active Co(IV) species, and reduce the energy barrier of the rate-determing step (RDS), thereby enhancing the OER activity. This work not only provides an informative picture to understand the complicated dependence of OER kinetics on electrolyte cations, but also sheds light on understanding the mechanism of other electrolyte cation-targeted electrocatalysis.

Unveiling the Electrolyte Cations Dependent Kinetics on CoOOH‐Catalyzed Oxygen Evolution Reaction

AbstractThe electrolyte cations‐dependent kinetics have been widely observed in many fields of electrocatalysis, however, the exact mechanism of the influence on catalytic performance is still a controversial topic of considerable discussion. Herein, combined with operando X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM), we verify that the electrolyte cations could intercalate into the layer of pristine CoOOH catalyst during the oxygen evolution reaction (OER) process, while the bigger cations lead to enlarged interlayer spacing and increased OER activity, following the order Cs+&gt;K+&gt;Na+&gt;Li+. X‐ray absorption spectroscopy (XAS), in situ Raman, in situ Ultraviolet‐visible (UV/Vis) spectroscopy, in situ XAS spectroscopy, cyclic voltammetry (CV), and theoretical calculations reveal that the intercalation of electrolyte cations efficiently modify the oxidation states of Co by enlarging the Co−O bonds, which in turn enhance the d‐band center of Co, optimize the adsorption strength of oxygen intermediates, facilitate the formation of OER active Co(IV) species, and reduce the energy barrier of the rate‐determing step (RDS), thereby enhancing the OER activity. This work not only provides an informative picture to understand the complicated dependence of OER kinetics on electrolyte cations, but also sheds light on understanding the mechanism of other electrolyte cation‐targeted electrocatalysis.

Superior performance of an anion exchange membrane water electrolyzer: Sequential electrodeposited Co-based oxygen evolution catalyst

Green hydrogen production in the anion exchange membrane water electrolysis (AEMWE) field requires catalysts for the oxygen evolution reaction (OER) with high performance, low cost, and ease of fabrication. Here, we report a sequential electrodeposited Co-based electrode supported on FeOxHy (Fe@Co) as a superior anode in alkaline media. The Fe@Co electrode exhibited an overpotential of 184 mV at 10 mA cm−2 with a Tafel slope of 44 mV per decade in 1 M KOH solution. In an AEMWE single-cell, it showed a current density of 1,780 mA cm−2 at 1.8 V at 50 °C, outperforming the state-of-the-art OER catalysts. This notable OER performance was attributed to the Fe-based support, which not only increased the active sites and oxidation state of Co but also formed Fe active sites. By comparing with other support materials and adjusting the method for synthesizing Fe, it was confirmed that Fe@Co has the highest OER activity. Our discovery and analysis of the sequential electroplating strategy provide an innovative perspective in the field of non-noble-metal AEMWE, which is a step forward toward cost-effective green hydrogen generation for the oncoming hydrogen economy.

Investigation on Reaction Mechanism in an SOFC Composite Cathode by Using Patterned Thin Film Electrodes

Introduction For the further commercial use of solid oxide fuel cells (SOFCs), operating at intermediate temperatures is demanded. When reducing the operating temperature, the degradation of cathodic activity occupies the largest part of degradation of cell performance. Therefore, to improve the performance of SOFCs at intermediate temperature, the activity of cathodic reaction has to be improved.The cathodic reaction of SOFCs proceeds not only at triple phase boundaries (TPBs) of electrode, electrolyte and gas but also at double phase boundaries (DPBs) of electrode and gas, when a mixed ionic and electronic conductor (MIEC) is used. Thus, increasing the DPB area is considered as the best way to improve the cathodic performance. However, it was reported that composite cathodes of MIEC and electrolyte particles showed better performance than simple MIEC cathodes, despite the DPB area decreased [1]. Possible reasons for such performance enhancement can be considered as (i) promotion of oxide ion diffusion and/or (ii) the increase of TPB concentration. However, the reason for the performance enhancement by making a composite cathode are not-well understood so far.In this study, we aimed to understand the cathodic reaction in a composite cathode of MIEC and electrolyte. For this purpose, we proposed new types of original model electrodes to simulate the reaction in actual porous composite electrodes. From electrochemical and the operando X-ray absorption spectroscopic measurements of the model electrodes, we tried to separately evaluate the contribution of ion diffusion and TPB reactions on the performance improvement of composite cathode. Methods When using a porous electrode, it is difficult to investigate the reaction mechanism because of its complicated microstructures. Our research group proposed so-called “patterned thin film model electrode” like Figure 1(a) as a model electrode to reproduce the reaction in a porous electrode while removing the influence of microstructure [2]. In this model electrode, the contact area of electrode and electrolyte was limited by partially inserting an insulating layer, and thus the reaction distribution was formed in the electrode as a function of the distance from the electrode/electrolyte interface.In this study, we proposed two new types of model electrodes as Figure 1(b) and 1(c) to simulate the porous composite electrode. In the patterned composite electrode (b), an electrolyte layer was inserted between the electrode and insulator. On the other hand, in the patterned composite electrode (c), a part of electrode was removed to introduce TPBs. From the difference between the model electrodes (a) and (b), the contribution of oxide ion diffusion in composite electrode was estimated. From the difference between the model electrodes (b) and (c) the contribution of the TPB reaction was estimated. In this study, we selected La0.6Sr0.4CoO3-δ (LSC64) as an MIEC cathode and Gd0.1Ce0.9O2-δ (GDC10) as an electrolyte material. Operando micro X-ray absorption spectroscopy (μ-XAS) measurement was conducted with the model electrodes to investigate the effective reaction area of the model electrode. In this measurement, a change in the oxygen chemical potential can be detected as a change of X-ray absorbance at the fixed energy near the Co K-edge accompanying a change of the oxidation state of Co in the LSC64 [3]. Thus, the reaction distribution could be evaluated by measuring the change of the X-ray absorbance due to the polarization as a function of the distance from the electrode/electrolyte interface. Results and Discussion Figure 2 shows the results of μ-XAS measurement at 973 K under 1 bar O2 with cathodic polarization. The area where the ratio of absorbance is larger than 1 corresponds to the area where the oxygen chemical potential is changed due to the polarization, i.e. the effective reaction area. The reaction area of the model electrode (b) was longer than that of the model electrode (a). This suggested oxide ion diffusion was improved by inserting the GDC layer. On the other hand, the reaction area of the model electrode (c) was longer than that of the model electrode (b). Generally, the reaction on the mixed conducting LSC64 electrode is supposed to proceed DPB reaction mainly. However, the longer reaction area of model electrode (c) indicated that the contribution of TPB reaction was also significant in the LSC64 composite electrode. As a conclusion, both promotion of oxide diffusion and the increase of TPB effective for the enhancement of the cathodic reaction in MIEC composite electrode.[1] Y. T. Kim, et al., Solid State Ionics, 309, 77-85 (2017).[2] K. Amezawa, et al., ECS transactions, 62(2), 129-135 (2015).[3] Y. Orikasa, et al., Journal of Physical Chemistry C, 115, 16433–16438 (2011). Figure 1

Understanding the Catalytic Active Sites of Crystalline CoSbxOy for Electrochemical Chlorine Evolution.

The chlorine evolution reaction (CER) is a key reaction in electrochemical oxidation (EO) of water treatment. Conventional anodes based on platinum group metals can be prohibitively expensive, which hinders further application of EO systems. Crystalline cobalt antimonate (CoSbxOy) was recently identified as a promising alternative to conventional anodes due to its high catalytic activity and stability in acidic media. However, its catalytic sites and reaction mechanism have not yet been elucidated. This study sheds light on the catalytically active sites in crystalline CoSbxOy anodes by using scanning electrochemical microscopy to compare the CER catalytic activities of a series of anode samples with different bulk Sb/Co ratios (from 1.43 to 2.80). The results showed that Sb sites served as more active catalytic sites than the Co sites. The varied Sb/Co ratios were also linked with slightly different electronic states of each element, leading to different CER selectivities in 30 mM chloride solutions under 10 mA cm-2 current density. The high activity of Sb sites toward the CER highlighted the significance of the electronic polarization that changed the oxidation states of Co and Sb.

Deciphering structural changes in LiNixMnyCozO2 cathodes of Li ion batteries during cycling: Experimental and theoretical investigations

Layered oxide material LiNixMnyCozO2 is emerging out as promising cathode for new generation of Li-ion batteries, especially as power sources for electric vehicles and plug-in hybrid vehicles. In this work, structural and electronic changes occurring in LiNixMnyCozO2 (LNMC) cathode materials during charge/discharge cycle of the battery is studied over a wide composition range using in-situ X-ray diffraction (XRD) and in-situ X-ray absorption spectroscopy (XAS) techniques. While in-situ XRD measurements decipher the overall structural changes during the charging/discharging cycles, in-situ element specific XAS measurements reveal site specific information on electronic and local structural changes. It has been found that for the LNMC samples the major charge compensation at the metal site during charging or Li ion de-intercalation is achieved by oxidation of Ni2+ ions without significant change in the oxidation state of Co or Mn ions. It is also found that local structure around Ni undergoes reversible change during charging and discharging cycles whereas local structure around Co or Mn sites show no significant change. Moreover, it has been found that local structural changes at Ni sites in the samples with higher Ni concentrations are much less compared to that in the samples with lower Ni concentrations during charging/discharging cycles, the result being corroborated by ab-initio theoretical simulations also. This is a new finding and would have significant implications in determining the optimum composition of LNMC electrodes of Li ion batteries for commercial applications.

Dewetting Transition of CoO/Pt(111) in CO Oxidation Conditions Observed In Situ by Ambient Pressure STM and XPS

Dewetting Transition of CoO/Pt(111) in CO Oxidation Conditions Observed In Situ by Ambient Pressure STM and XPS

Structural and Composition Evolution of Palladium Catalyst for CO Oxidation under Steady-State Reaction Conditions

Understanding how the composition and structure of heterogeneous catalysts change during in situ reaction is of critical importance but greatly challenging because of the complexity of multiple time–space scale. Herein, we propose a self-adaptive simulation strategy driven by the first-principles microkinetic modeling and genetic-algorithm-based global structural search accelerated by machine learning that allows the interplay of surface reaction and catalyst evolution, and uncover the structural/compositional evolution of a Pd(111) single-crystal catalyst under the reaction conditions for CO oxidation, which is a classic open problem lasting for decades. The possible active phases at the kinetically steady state are identified and their common nature is unraveled. We show that, in the presence of CO/O2 reaction mixtures, a dynamically stable partially oxidized nonstoichiometric palladium oxide (PdO0.44 layer) grown on Pd(111) is formed with the O adatoms inserted into the Pd(111) sublayer that drives the formation of the surface oxide. Remarkably, the first-principles microkinetic analyses demonstrate that this self-evolved PdO0.44 surface at the steady state exhibits higher catalytic activity for CO oxidation as compared with Pd(111) and overoxidized PdO catalyst, which may explain the long-standing puzzle of the “PdOx” active phase for Pd catalyst during CO oxidation.

Comparison of lithium sulphate borate glass cathode materials with single Mn and Co doping and dual Mn–Co doping

Single Mn and Co doping to dual Co and Mn ions in lithium sulphate (Li2S) borate-based glasses system is carefully studied as new glass cathode for future Li-ion battery. The B–O bonding in glass network and the oxidation states of Co, Mn and S ions in glass structure are investigated using synchrotron-based IR spectroscopy and XANES. The pseudo-capacitance behavior of the CV curves indicates and confirms that Co2+/Co3+ and Mn2+/Mn3+ are in mixed oxidation states. Surprisingly, in this work, the 3Mn5Co glass composition exhibits the highest specific capacitance value of 121.12 F g−1. This shows a better enhancement of electrochemical properties using dual Mn–Co doping in glass structure rather than a single doping.

Identification of high ionic conducting members (M(III) = Co, Ni) in the new lithium rich Li4.50M0.50TeO6 (M(III) = Co, Ni, In) series.

Many new lithium-excess compounds with rock-salt related structures have been extensively studied in recent years to discover high-capacity electrode materials for lithium-ion batteries. In the present work, lithium rich layered tellurates, Li4.50M0.50TeO6 (M(III) = Co, Ni, In), are added to the existing series of Li4.50M0.50TeO6 (M(III) = Cr, Mn, Fe, Al, and Ga) oxides. Structural investigations revealed their stabilization in the space group C2/m with a new cationic ordering. The structure consists of (Li1.50M0.50TeO6)3- honeycomb arrays along the ab plane by the edge sharing of TeO6 with (Li/M)O6 octahedra. The honeycomb arrays are separated by the intermediate layer of Li alone in Li4.50Co0.50TeO6. On the other hand, in the Ni and In analogues, the interlayer region consists of Li with Te, and Li with In ions, respectively. XPS studies confirmed the +3 oxidation state of Co and Ni ions. The appearance of a strong band at 680 nm resulting from LMCT (O → Co) in the UV-vis DRS data of the Li4.50Co0.50TeO6 sample further indicated the presence of Co3+ (d6, low spin) ions. The absence of characteristic Ni2+ bands at around ∼650 and 740 nm supported Ni3+ ions. Li4.50Co0.50TeO6 showed diamagnetic behaviour, while Li4.50Ni0.50TeO6 displayed paramagnetic nature. A negative θ (-14(2)) K has been obtained in the temperature region of 300-100 K for Li4.50Ni0.50TeO6 representing dominant antiferromagnetic interactions. At 2 K, Li4.50Ni0.50TeO6 unveiled a non-linear trend with no significant hysteresis and nearly saturation at 5 T field indicating the existence of additional interactions. Li4.50Co0.50TeO6 and Li4.50Ni0.50TeO6 exhibited significant conductivity values of 0.016 and 0.003 S cm-1, respectively, at 300 °C, thereby opening up further studies in this direction.

Rational design of cobalt catalysts embedded in N-Doped carbon for the alcohol dehydrogenation to carboxylic acids

In this work, a series of Co catalysts (namely Co@NC) was designed and developed from the thermal treatment of ZIF-67. Through extensive screening of various parameters, Co@NC700-H2/Ar exhibited the best catalytic performance in the acceptorless alcohol dehydrogenation to carboxylic acids. It was worth noting that Co@NC700-H2/Ar enabled the efficient synthesis of various aromatic and aliphatic carboxylic acids in moderate to high yields. Besides, it was recyclable for 9 consecutive cycles without activity decay. Moreover, the effects of pyrolysis conditions on the catalytic performance of the resulting materials were thoroughly examined, and the rationale for the superiority of Co@NC700-H2/Ar over the other prepared materials was also provided. Specifically, the pyrolysis atmosphere applying 95% of Ar gas and 5% of H2 gas (H2/Ar) resulted in the generation of ideal porosity and carbon nanotubes (CNTs), while utilizing 700 °C as the optimized pyrolysis temperature was ascribed to the comprehensive evaluation of materials crystallinity and defective structures. Furthermore, additional insights were gained by systematically exploring the oxidation states of Co in different catalysts. It was proposed that the Co–N species played a crucial role in this catalysis, while the contribution of other Co species, including Co0 and Co–O, could not be neglected. Finally, a plausible reaction mechanism was proposed based on the above observations and related literature reports.

Transformation of Waste Toner Powder into Valuable Fe2O3 Nanoparticles for the Preparation of Recyclable Co(II)-NH2-SiO2@Fe2O3 and Its Applications in the Synthesis of Polyhydroquinoline and Quinazoline Derivatives.

Ecological recycling of waste materials by converting them into valuable nanomaterials can be considered a great opportunity for management and fortification of the environment. This article deals with the environment-friendly synthesis of Fe2O3 nanoparticles (composed of α-Fe2O3 and γ-Fe2O3) using waste toner powder (WTP) via calcination. Fe2O3 nanoparticles were then coated with silica using TEOS, functionalized with silane (APTMS), and immobilized with Co(II) to get the desired biocompatible and cost-effective catalyst, i.e., Co(II)-NH2-SiO2@Fe2O3. The structural features in terms of evaluation of morphology, particle size, presence of functional groups, polycrystallinity, and metal content over the surface were determined by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (P-XRD), field emission gun-scanning electron microscopy (FEG-SEM), energy-dispersive X-ray analysis (EDX), high resolution-transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET) analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) studies. XPS confirmed the (II) oxidation state of Co, and ICP-AES and EDX supported the loading of Co(II) over the surface of the support. P-XRD proved the polycrystalline nature of the Fe2O3 core and even after functionalization. In comparison to previously reported methods, Co(II)-NH2-SiO2@Fe2O3 provides an eco-friendly procedure for the synthesis of polyhydroquinoline and quinazoline derivatives with several advantages such as a short reaction time and high yield. Polyhydroquinoline and quinazoline derivatives are important scaffolds in pharmacologically active compounds. Moreover, the developed nanocatalyst was recyclable, and HR-TEM and P-XRD confirmed the agglomeration in the recycled catalyst resulted in a decrease in yield after the fifth run. The present protocol provides a new strategy of recycling e-waste into a heterogeneous nanocatalyst for the synthesis of heterocycles via multicomponent reactions. This made the synthesized catalyst convincingly more superior to other previously reported catalysts for organic transformations.

Electrocatalytic behaviour of Cu-substituted La0.5Sr0.5Co0.8Fe0.2-xCuxO3-δ (x = 0–0.2) perovskite oxides

In this study, a series of La0.5Sr0.5Co0.8Fe0.2-xCuxO3-δ (x ​= ​0–0.2) perovskite oxides were synthesized following solution combustion technique. This elucidation highlights the role of partly substituted Cu on the OER performance of perovskite in alkaline media. XRD, BET surface area analysis, and XPS techniques were used to investigate the physio-chemical properties of the synthesized samples. XPS results revealed that partial substitution of Fe with Cu changed the oxidation states of Co and Fe (B-site) and substantially enhanced oxygen nonstoichiometry. Among the studied oxides, La0.5Sr0.5Co0.8Cu0.2O3-δ oxide showed the highest catalytic activities in 1 ​M KOH for OER with a lower onset potential, over potential, and Tafel slope of 1.51 ​V, 500 ​mV, and 60.54 ​mV dec−1 respectively with better long-term stability. Our findings indicate that La0.5Sr0.5Co0.8Cu0.2O3-δ perovskite amends intrinsic properties providing efficient OER performance and may act as a more suitable electrocatalyst for OER application.