Cobalt Carbide Research Articles

Cobalt Carbide–Nickel Carbide Nanosheets Supported on CoNi Basic Carbonates/Stainless Steel Mesh as a Trifunctional Catalyst for Water Splitting and Zn-Air Batteries

Cobalt Carbide–Nickel Carbide Nanosheets Supported on CoNi Basic Carbonates/Stainless Steel Mesh as a Trifunctional Catalyst for Water Splitting and Zn-Air Batteries

Co-Co6Mo6C2 heterostructure grown on carbon nanofibers as tri-functional electrocatalyst for overall water splitting and rechargeable Zn-air batteries

The advancement of cost-effective and efficient electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is crucial for the progress of clean energy conversion and storage technologies. In this work, cobalt (Co) and cobalt-molybdenum (Mo) bimetallic carbide (Co6Mo6C2) heterostructure grown on carbon nanofibers (denoted as Co-Co6Mo6C2/CNFs) as tri-functional electrocatalyst were prepared by a four-step method. Benefiting from the electronic structure modulation between the heterostructure to improve the catalytic activity, Co-Co6Mo6C2/CNFs exhibits high catalytic activity for HER (91 mV @ 10 mA cm−2), OER (293 mV @ 10 mA cm−2) and ORR (E1/2=0.80 V). Moreover, Co-Co6Mo6C2/CNFs assembled overall water splitting electrolyzer achieves a current density of 10 mA cm−2 with a battery voltage of only 1.70 V and has long-term durability. Zn-air batteries (ZABs) based on Co-Co6Mo6C2/CNFs has a power density of 156.6 mW cm−2 with good stability. This study contributes to the development of inexpensive and efficient transition metal-based multifunctional electrocatalysts.

Preparation of hard magnetic Co2C nanospheres as electrocatalysts for hydrogen evolution reaction

Cobalt carbide as a new type of transition metal carbides (TMACs) has received extensive attention in the field of magnetism and electrocatalysis. As one of the cobalt carbide materials, Co2C shows good hard magnetism. In this paper, we have designed a simple and efficient method to successfully prepare single-phase Co2C nanospheres. Co2C is synthesized by using Co3O4 as precursor and small molecule amino ethylenediamine as carbon source. The material exhibits excellent hard magnetic properties, with saturation magnetization up (Ms) to 32.19 emu/g and coercivity up to 1111 Oe at room temperature. Co2C also demonstrats excellent hydrogen evolution reaction performance in 1 M KOH solution. Using nickel foam as the working electrode, the overpotential of only 92 mV can reach the current density of 10 mA cm−2, and the Tafel slope is 104 mV dec−1. This provides a new idea for the further development of synthetic cobalt carbide and its composite materials.

Flexible multifunctional magnetic-conductive Janus nanocomposite films towards highly-efficient electromagnetic interference shielding and thermal management

The rapid development of aerospace, intelligent wearable electronics and 5G communications puts forward higher demands for electromagnetic interference (EMI) shielding materials. Herein, the flexible multifunctional magnetic-conductive Janus nanocomposite films with magnetic cobalt carbide nanowires/bacterial cellulose (Co@C NW/BC) blends as the upper side, and conductive Ti3C2Tx MXene as the bottom side are obtained via the layer-by-layer (LBL) vacuum assisted filtration-hot pressing method. The two magnetic and conductive sides endow the Janus nanocomposite films with distinctly different performances in EMI shielding and thermal management. When the electromagnetic waves are incident from Co@C NW/BC side, the films exhibit a high EMI shielding effectiveness (EMI SE) of 49.8 dB with an enhanced microwave absorption (SEA) of 33.9 dB at the ultralow thickness of 43 μm. Meanwhile, the Ti3C2Tx side exhibits improved electrical heating performances with a surface temperature of 120 °C at 6 V voltage, increased photothermal conversion temperature of 77.8 °C upon 2.0 kW/m2 light intensity, as well as excellent thermal stealth properties with a low radiation temperature of 88.4 °C on the 240 °C hot stage. Moreover, the Janus nanocomposite films show a high tensile strength of 80.0 MPa. The resultant Janus nanocomposite films possess great application prospects in highly-efficient EMI shielding and thermal management.

Hydrocarbon Formation from Syngas with In-Operando Monitoring of Cobalt- and Manganese-Based (pre)Catalysts Using X-ray Diffraction.

Two-layered metal oxides (LiCoO2 and cobalt-doped K n MnO2, n < 1) were explored as precatalysts for nanoconfined cobalt-based Fischer-Tropsch catalysts for conversion of syngas (CO and H2) to hydrocarbons. Ex situ, in situ, and PDF XRD analyses are presented. Based on in situ XRD analysis, LiCoO2 underwent reduction to predominantly cubic and hexagonal phases of cobalt metal. Reaction with syngas resulted in the generation of carbon, cobalt carbide, and lithium carbonate, in addition to the metallic cobalt phases. In the case of cobalt-doped birnessite, catalyst activation converted the birnessite phase to manganite and the cobalt to elemental cobalt, along with similar lithium and carbon phases. Conversion of syngas to C1 through C7 products was observed. The best conversions were observed for the LiCoO2 precursor catalyst, with generally a low olefin-to-paraffin ratio. While the conversions for the cobalt-doped birnessite precatalyst were generally lower, with lower chain lengths (up to C5), these catalysts gave a strikingly high olefin-to-paraffin ratio: in the best case, greater than 20:1.

Visualizing Phase Evolution of Co2C for Efficient Fischer-Tropsch to Olefins.

Cobalt carbide (Co2C) possesses high catalytic efficiency Fischer-Tropsch synthesis (FTS), while the products selectivity appears sensitive to crystallography geometry. Since the Anderson-Schulz-Flory (ASF) distribution in FTS is broken through fabricating facetted Co2C nanocrystals, yet the underlying mechanism of Co2C crystallization remains unclarified suffering from sophisticated catalyst composition involving promoter agents. Herein, the synthesis of high-purity single-crystal nanoprisms (Co2C-p) for highly efficient FTS is reported to lower olefins. Through comprehensive microstructure analysis, e.g., high-resolution TEM, in situ TEM and electron diffraction, as well as finite element simulation of gas flow field, for the first time the full roadmap of forming catalytic active cobalt carbides is disclosed, starting from reduction of Co3O4 precursor to CoO intermediate, then carburization into Co2C-s and subsequent ripening growth into Co2C-p. This gas-induced engineering of crystal phase provides a new synthesis strategy, with many new possibilities for precise design of metal-based catalyst for diverse catalytic applications.

Effects of Co3C formation on the catalytic performance for Fischer-Tropsch synthesis over Co/SiO2 catalysts

Cobalt carbides demonstrate higher selectivity towards light olefins and alcohols in the Fischer-Tropsch synthesis (FTS). In this study, we present an investigation of a series of supported cobalt catalysts that were carburized with CO for different time. The presence of Co3CCo, Co and Co2CCo phases in these catalysts was confirmed through Transmission Electron Microscopy (TEM). The Co/SiO2-RC-0.5 h catalyst with both Co3C and Co structure exhibits the highest CO conversion for the FTS reaction. By utilizing the chemisorption techniques, we studied the structure-performance relationships between the phase and activity, and confirmed that Co3C has the highest intrinsic activity, which is beneficial for CO activation. This study provides further insight into the positive effects of Co3C on the FTS reaction and guides us in the rational design of high active Co-based FTS catalysts.

The properties of the powder that makes the basis of hard alloys used in the crushing of underground resources

Today, many countries are extraction the underground resources (non-ferrous and rare metals) by having a leading processing plants. In Uzbekistan, metals such as gold, silver, copper, uranium, rhenium, and tungsten are mined from underground resources and produced as finished products. A significant part of the costs of the extraction of underground resources is spent on the processes of crushing and grinding crushing minerals. Hard alloys used in the process of crushing and grinding ores are produced based on metals such as tungsten and cobalt. This article presents scientific-practical research on the properties of powders that form the basis of tungsten carbide-cobalt-based hard alloys used in crushing underground resources. During the research, the chemical composition of tungsten and cobalt carbide powders chosen as raw materials, the location of the powders in the raw materials, the granulometric sizes of the powders, and their morphology were studied. In all conducted studies, tungsten carbide powders produced at the JSC “Almalyk MMC” were used as a raw material to prepare samples of tungsten carbide-cobalt-based hard alloys and also as a binder. Cobalt powder produced in this enterprise was selected. All studies were carried out on a scanning electron microscope, JSM-IT200 (JEOL, Japan), at the Uzbekistan-Japan Youth Innovation Center.

Effect of Pulse Conditions on Machining Characteristics in Bipolar-Pulse Electrochemical Machining of Cemented Carbide

Electrochemical machining was performed on two cemented carbides with different compositions using unipolar and bipolar short-pulse voltages to investigate the effects of the composition and pulse conditions on the machining characteristics. In the case of cemented carbides with high cobalt and low tungsten carbide (WC) contents, machining progressed even when a unipolar voltage was used. This is believed to be due to the dissolution of the binder, that is, Co, which causes the WC and WO3 particles to drop out. Machining progressed more easily when a bipolar voltage was used than when a unipolar voltage was used. This is attributed to the effective removal of WO3. The unevenness of the machined surface was also reduced with bipolar voltage. The negative pulse duration had to be sufficiently but appropriately long, because too long a duration increased the wear of the tool electrode. Even when bipolar pulse voltages were used, similar to the machining of general materials, a shorter positive pulse duration resulted in more precise machining. However, in the case of cemented carbide with low Co and high WC contents, the removal did not progress when a unipolar pulse voltage was applied. On the other hand, the machining progressed when a bipolar voltage was applied. However, if the positive pulse duration was excessively long, the amount of removal decreased. This is believed to be because the longer positive pulse duration increased the amount of WO3 generated, thereby inhibiting the current flow. Therefore, it is necessary to set an appropriate positive pulse duration to avoid the excessive production of WO3.

Controlled synthesis and photocatalytic hydrogen evolution activities of cobalt carbides with different phase compositions

Cobalt carbides are emerging as promising materials for various magnetic and catalytic applications. However, exploring dedicated cobalt carbides with optimal catalytic properties via adjusting phase compositions remains a significant challenge. Herein, three different cobalt carbides, Co x C (Co2C-Co3C), Co2C-Co, and Co3C, were successfully prepared using a facile one-pot green method. The phase compositions of cobalt carbides could be easily controlled by varying the cobalt-based precursors and carbon sources. More remarkably, three different cobalt carbides could serve as reduction cocatalysts decorated CdS for improved hydrogen production under visible light. Intriguingly, the obtained Co3C/CdS nanocomposite displayed the highest photocatalytic hydrogen evolution activity among the three composites and superior photocatalytic stability. This work provides a fundamental approach to tuning the photocatalytic properties of cobalt carbides for energy conversion fields.

Theoretical investigation of the selectivity of alcohols and aldehydes on Co-based catalysts in syngas conversion

Syngas conversion to long chain alcohols and aldehydes by Co-based catalysts offers green route for synthesizing value-added chemicals. Cobalt carbides (Co2C) has been proven promoting oxygenates formation, and the Co/Co2C interface exhibited synergetic effects on increasing selectivity of higher alcohols. However, the underlying mechanism that determines the ratio of aldehydes and alcohols in oxygenate products is less understood. In this work, the hydrogenation of oxygenate intermediate was studied from first principles on metallic Co, Co2C surfaces and Co/Co2C interface to investigate the formation processes of alcohols and aldehydes. First-principles calculations show that: On Co2C(111) facet of Co2C nanosphere, aldehyde desorption as the final product has a slight advantage over its subsequent hydrogenation to alcohol; hydrogenation of oxygenate on Co2C(020) facet of Co2C nanoprism is difficult, whereas aldehyde on Co2C(101) facet of Co2C nanoprism is very easy to be hydrogenated to alcohol; and the synergistic effect between metallic and carbide surfaces on the Co/Co2C interface model promotes the selectivity of alcohol as the final product during hydrogenation of oxygenate intermediates. This study provides theoretical insights into the rational design of catalysts for controlling the selectivity between aldehydes and alcohols in syngas conversion to oxygenates.

Manganese as a structural promoter in silica-supported cobalt Fischer-Tropsch catalysts under simulated high conversion conditions

Understanding the deactivation mechanism of cobalt-based Fischer-Tropsch catalysts is of significant practical importance. Herein, we explored the role of manganese as a structural promoter on silica-supported cobalt nanoparticles under simulated high CO conversion conditions, i.e., high relative humidity. The structural changes in cobalt dispersion and oxidation state were followed by in situ Mössbauer emission spectroscopy. Adding manganese oxide to silica-supported cobalt enhanced the dispersion of metallic cobalt in the reduced catalysts. This higher cobalt dispersion, however, led to a stronger tendency of cobalt silicate formation under humid conditions. Without manganese, the cobalt particles sintered, and the larger ones were prone to transformation into cobalt carbide under high conversion conditions. As such, silica is not preferred as a support for practical FTS.

Stabilizing Co2C with H2O and K promoter for CO2 hydrogenation to C2+ hydrocarbons.

The decomposition of cobalt carbide (Co2C) to metallic cobalt in CO2 hydrogenation results in a notable drop in the selectivity of valued C2+ products, and the stabilization of Co2C remains a grand challenge. Here, we report an in situ synthesized K-Co2C catalyst, and the selectivity of C2+ hydrocarbons in CO2 hydrogenation achieves 67.3% at 300°C, 3.0 MPa. Experimental and theoretical results elucidate that CoO transforms to Co2C in the reaction, while the stabilization of Co2C is dependent on the reaction atmosphere and the K promoter. During the carburization, the K promoter and H2O jointly assist in the formation of surface C* species via the carboxylate intermediate, while the adsorption of C* on CoO is enhanced by the K promoter. The lifetime of the K-Co2C is further prolonged from 35 hours to over 200 hours by co-feeding H2O. This work provides a fundamental understanding toward the role of H2O in Co2C chemistry, as well as the potential of extending its application in other reactions.

Toward understanding Fischer − Tropsch synthesis on cobalt carbides from first principles and microkinetic analysis

Cobalt carbides (Co2C) have been recognized as crucial active phases in emerging applications for direct producing high-value chemicals including oxygenates and olefins from syngas. A mechanistic understanding of the complex nature of the surface reactions on Co2C is vital but remains incompletely investigated. In this work, a comprehensive reaction network analysis on Co2C(111) facet by first-principles-based microkinetics modeling reveals pathways for generating methane, ethane, ethylene, acetaldehyde, ethanol and C3 + products, and the model-predicted product distribution as a function of temperature can reflect experimental observations. The competition between the formation of hydrocarbon and oxygenates was analyzed in detail, on both an energetic and microkinetic basis. The elementary reaction steps that control the selectivity of desired products were quantitatively determined using the concept of degree of selectivity control (DSC). Underlying mechanisms for chain growth and product formation were discussed, altogether to provide a better understanding of Fischer − Tropsch synthesis on cobalt carbides.

Tuning cobalt carbide wettability environment for Fischer-Tropsch to olefins with high carbon efficiency

Fischer-Tropsch synthesis to olefins (FTO) with high carbon efficiency is an important but challenging research target. Current routes for direct syngas conversion to olefins suffer from high CO2 selectivity and low olefin yields due to the inevitable water-gas shift (WGS) reaction. Herein, we report that product selectivity can be controlled by tuning the wettability of the environment around the active center through simple physical mixing of cobalt carbide (Co2C) with a hydrophobic SiO2 component. The suppressed WGS reactivity results in a greatly improved catalytic performance of Co2C, significantly decreased CO2 selectivity (from 47.8% to 16.8%), and increased olefin selectivity (by ~65%) and activity (by 30%). The local hydrophobic environment favors the rapid diffusion of water away from the Co2C active center, thus remarkably enhancing the linear adsorption of CO and suppressing the production of CO2via WGS. This work provides a simple yet effective strategy to modulate the product selectivity and improve the carbon efficiency of the FTO process.

Large-Scale Synthesis of Multifunctional Single-Phase Co2 C Nanomaterials.

Achieving scalable synthesis of nanoscale transition-metal carbides (TMCs), regarded as substitutes for platinum-group noble metals, remains an ongoing challenge. Herein, a 100-g scale synthesis of single-phased cobalt carbide (Co2 C) through carburization of Co-based Prussian Blue Analog (Co-PBA) is reported in CO2 /H2 atmosphere under mild conditions (230 °C, ambient pressure). Textural property investigations indicate a successful preparation of orthorhombic-phased Co2 C nanomaterials with Pt-group-like electronic properties. As a demonstration, Co2 C achieves landmark photo-assisted thermal catalytic CO2 conversion rates with photo-switched product selectivity, which far exceeds the representative Pt-group-metal-based catalysts. This impressive result is attributed to the excellent activation of reactants, colorific light absorption, and photo-to-thermal conversion capacities. In addition to CO2 hydrogenation, the versatile Co2 C materials show huge prospects in antibacterial therapy, interfacial water evaporation, electrochemical hydrogen evolution reaction, and battery technologies. This study paves the way toward unlocking the potential of multi-functional Co2 C nanomaterials.

Similarities and trends in adsorbate induced reconstruction – Structure and stability of FCC iron and cobalt surface carbides

Thin FCC (100) iron and cobalt carbide films were prepared on Cu(100) to study the connection between their structure, electronic properties and stability. We present the first detailed, real space experimental confirmation of the C-induced clock reconstruction on the FCC(100) surfaces of iron and cobalt. Both Fe and Co surface carbides show p4g (2 × 2) surface reconstruction with tetracoordinated square planar carbon and pure FCC (100) metal layers underneath. Combining tip-sample distance dependent STM imaging with theoretical calculations we present different imaging modes of Fe2C. Using a combination of angle-resolved x-ray photoelectron spectroscopy (AR-XPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and theoretical calculations we provide detailed electronic and structural models for Fe2C and Co2C p4g (2 × 2) surface carbides and other 2D Fe2X interstitial compound systems. In various Fe2X (X = B, C, N, O) surface compounds moving to the right in the periodic table with increasing electrons the reconstruction becomes less favorable, while iron carbide shows the highest stability.

Ni, Co and Ni-Co-Modified Tungsten Carbides Obtained by an Electric Arc Method as Dry Reforming Catalysts

Dry reforming of methane (DRM), to produce synthesis gas, is one of the most important chemical reactions used for the industrial production of hydrogen and leads to the synthesis of hydrocarbons (liquid fuels) and other valuable products. A cost-effective alternative to active and stable noble metal DRM catalysts, with comparable catalytic performance, can be composite materials based on nickel, cobalt and transition metal carbides. In this line, the present work proposes a non-standard way to obtain dry reforming catalysts of Ni, Co and Ni-Co-modified tungsten carbide (WC) produced by an electric arc method. Different amounts of nickel, cobalt and their mixtures were deposited on tungsten carbide by deposition-precipitation with NaOH (DP) and incipient wetness impregnation (IWI) methods. The resulting materials were characterized by N2 adsorption-desorption, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and their performance was evaluated in DRM. The composition and preparation method of catalysts predetermined their structural, textural and electronic properties, playing a decisive role in their activity for DRM. DP-prepared 20%Ni/WC material remained resistant to oxidation, both that of the active metal (nickel) and of the tungsten carbide, as well as to coking during DRM. This sample proved to be the most active and stable among all studied materials. Possibly, the resistance to oxidation and coking was due to a more efficient implementation of the oxidation/(re)carbonization cycle on the surface of this catalyst.

Direct conversion of syngas to alpha olefins via Fischer–Tropsch synthesis: Process development and comparative techno-economic-environmental analysis

Under the pressure of carbon peak and carbon neutrality, coal chemical industry urgently needs to transform to high energy efficiency, low carbon emissions, and high-added value. A coal-based Fischer-Tropsch to olefins route using a new cobalt carbide nanoprisms catalyst for directly converting syngas into olefins was proposed in this study. To evaluate the feasibility and competitiveness of this route, we designed an products separation process and conducted a process simulation via Aspen plus based on laboratory data. On top of that, the energy consumption, energy efficiency, carbon emission, and economic performance of the coal-based Fischer–Tropsch to olefins route were analyzed, in comparison with coal-based methanol to olefins route. The energy consumption of the proposed route is 10.1% lower than that of coal-based methanol to olefins, and its carbon emissions factor is 14.8% lower than that of coal-based methanol to olefins. When the mass weighted product price is 1504 US $/ton, the project's financial internal rate of return of 17.39% is significantly greater than the industry's benchmark internal rate of return of 12%, indicating that the proposed route has strong economic competitiveness. Finally, several suggestions are proposed to improve the comprehensive performance of the proposed route for its sustainable development.

Catalytic Performance of Alumina-Supported Cobalt Carbide Catalysts for Low-Temperature Fischer–Tropsch Synthesis

The determination of the catalyst’s active phase helps improve the catalytic performance of the Fischer–Tropsch (FT) synthesis. Different phases of cobalt, including cobalt oxide, carbide, and metal, exist during the reaction. The content of each phase can affect the catalytic performance and product distribution. In this study, a series of cobalt carbide catalysts were synthesized by exposure of Co/Al2O3 catalyst to CH4 at different temperatures from 300 °C to 800 °C. The physicochemical properties of the carbide catalysts (CoCx/Al2O3) were evaluated by different characterization methods. The catalytic performances of the catalysts were investigated in an autoclave reactor to determine the role of cobalt carbides on the CO conversion and product distribution during the reaction. XRD and XPS analysis confirmed the presence of Co2C in the prepared catalysts. The higher carbidation temperature resulted in the decomposition of methane into hydrogen and carbon, and the presence of graphitic carbon was confirmed by XRD, XPS, SEM, and Raman analysis. The Co2C also decomposed to metallic cobalt and carbon, and the content of cobalt carbide decreased at higher carbidation temperatures. Higher content of Co2C resulted in a lower CO conversion and higher selectivity to light alkanes, mainly methane. The higher carbidation temperature resulted in the decomposition of Co2C to metallic cobalt with higher activity in the FT reaction. The CO conversion increased by increasing the carbidation temperature from 300 °C to 800 °C, due to the higher content of metallic cobalt. In the presence of pure hydrogen, the Co2C could be converted mainly into hexagonal, close-packed (hcp) Co with higher activity for dissociative adsorption of CO, which resulted in higher catalyst activity and selectivity to heavier hydrocarbons.