Cobalt Molybdenum Nitride Research Articles

Synthesis of Cobalt Molybdenum Nitrides From Precursors Precipitated at Different pH

AbstractCobalt molybdenum nitrides can be obtained from the oxidic precursor by reaction with gaseous ammonia. Despite the large number of works regarding the catalytical properties of these compounds, there are relatively few reports about the initial transformation from oxide to nitride. In this work, the influence of the precursor structure on the active phase formation and catalytic properties of cobalt molybdenum nitrides is examined. Oxidic precursors were obtained by precipitation at different pH values controlled by the addition of aqueous ammonia. The parameters of the precipitation process affected the composition and properties of the materials. The ammonolysis of NH4Co2OH(MoO4)2 ⋅ H2O was investigated in situ with the use of X‐ray powder diffraction and thermogravimetry. The ammonia synthesis activity of the obtained catalysts was compared to the reference iron catalyst. The formation of the Co3Mo intermetallic phase was suggested as the factor governing high activity.

Surface Reconstruction on Metal Nitride during Photo-oxidation.

The efficient conversion and storage of solar energy for chemical fuel production presents a challenge in sustainable energy technologies. Metal nitrides (MNs) possess unique structures that make them multi-functional catalysts for water splitting. However, the thermodynamic instability of MNs often results in the formation of surface oxide layers and ambiguous reaction mechanisms. Herein, we present on the photo-induced reconstruction of a Mo-rich@Co-rich bi-layer on ternary cobalt-molybdenum nitride (Co3 Mo3 N) surfaces, resulting in improved effectiveness for solar water splitting. During a photo-oxidation process, the uniform initial surface oxide layer is reconstructed into an amorphous Co-rich oxide surface layer and a subsurface Mo-N layer. The Co-rich outer layer provides active sites for photocatalytic oxygen evolution reaction (POER), while the Mo-rich sublayer promotes charge transfer and enhances the oxidation resistance of Co3 Mo3 N. Additionally, the surface reconstruction yields a shortened Co-Mo bond length, weakening the adsorption of hydrogen and resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and POER. This work provides insight into the surface structure-to-activity relationships of MNs in solar energy conversion, and is expected to have significant implications for the design of metal nitride-based catalysts in sustainable energy technologies.

The Influence of Potassium Promotion on the Structural Properties of Cobalt Molybdenum Nitrides in Ammonia Synthesis

Cobalt molybdenum nitrides are one of the most promising ammonia-synthesis catalysts of the future. However, the selection of the optimal promoter composition is a challenging task. In this paper, the structure–property relationship of ternary cobalt molybdenum nitrides as ammonia synthesis catalysts promoted with potassium was studied. A series of catalysts containing 0.2–3.5 wt% potassium was analyzed by means of X-ray diffraction, volumetric gas adsorption, and activity tests in ammonia synthesis. The catalysts were subjected to thermal aging in the same catalytical reactor. The influence of the potassium promoter on the thermostability was determined. The observed loss of activity in catalysts with a high potassium content was related to the concentration of Co2Mo3N and Co3Mo3N phases, the mean crystallite sizes, the specific surface area, and the pore size distribution.

Synthesis of cobalt molybdenum nitrides by a gas-solid reaction – In situ XRPD study

The solid-gas reaction of the physical mixtures of cobalt(II) nitrate hexahydrate and ammonium molybdate tetrahydrate with gaseous ammonia was studied. The process was examined with the use of in situ X-ray powder diffraction (XRPD). Mixtures of cobalt molybdenum nitrides Co2Mo3N and Co3Mo3N were obtained at 700 °C. CoMoO4, Co2Mo3O8, Mo2N and metallic cobalt were identified as intermediates. The presented synthesis method allows the direct route of cobalt molybdenum nitrides formation without the wet preparation of oxidic precursor.

Enhancing ammonia catalytic production over spatially confined cobalt molybdenum nitride nanoparticles in SBA-15

Ternary Co3Mo3N nitrides are reported to exhibit high catalytic activity in ammonia synthesis. However, synthesis of ternary nitrides requires thermal treatments at elevated temperatures and reactive atmospheres that lead to unavoidable surface reduction (∼ 10 m2 g-1). In this work, we have developed a novel approach to improve the catalytic activity of Co3Mo3N through its dispersion into a high surface area silica-based support (SBA-15). During ammonolysis and ammonia synthesis conditions reaction, SBA-15 demonstrated good thermal and chemical stability maintaining an ordered porous structure and high surface area (> 500 m2 g-1). For application in ammonia synthesis, SBA-15 supported cobalt molybdenum catalysts with different metal loading (10, 20 and 30 wt%) were prepared by a modified impregnation-infiltration protocol and their catalytic activity studied. The dispersion of CoMo nitride nanoparticles into SBA-15 structures resulted in the improvement of their structural and textural properties of nitrides as evidenced by XRD analysis, STEM-EDS, and N2- physisorption (e.g. 10-CoMo-N/SBA-15: 348 m2 g-1). Nevertheless, the surface composition of CoMo-N/SBA-15 catalysts was found to be similar to the non-supported Co3Mo3N. Furthermore, supported CoMo-N/SBA-15 displayed enhanced catalytic activity in ammonia synthesis (1714, 1429 and 810 µmol gactivephase-1 h-1 corresponding to the CoMo oxide loadings of 10, 20, 30 wt% respectively) that outperform the classical Co3Mo3N catalyst (259 µmol gcatalyst-1 h-1). The results reported in this work highlights a novel approach for the design of nitride-based catalysts with superior catalytic properties in ammonia synthesis.

Cobalt Molybdenum Nitride-Based Nanosheets for Seawater Splitting.

The development of cost-effective bifunctional catalysts for water electrolysis is both a crucial necessity and an exciting scientific challenge. Herein, a simple approach based on a metal-organic framework sacrificial template to preparing cobalt molybdenum nitride supported on nitrogen-doped carbon nanosheets is reported. The porous structure of produced composite enables fast reaction kinetics, enhanced stability, and high corrosion resistance in critical seawater conditions. The cobalt molybdenum nitride-based electrocatalyst is tested toward both oxygen evolution reaction and hydrogen evolution reaction half-reactions using the seawater electrolyte, providing excellent performances that are rationalized using density functional theory. Subsequently, the nitride composite is tested as a bifunctional catalyst for the overall splitting of KOH-treated seawater from the Mediterranean Sea. The assembled system requires overpotentials of just 1.70 V to achieve a current density of 100 mA cm-2 in 1 M KOH seawater and continuously works for over 62 h. This work demonstrates the potential of transition-metal nitrides for seawater splitting and represents a step forward toward the cost-effective implementation of this technology.

Highly Efficient Hydrogen Evolution in Alkaline Medium by Ternary Cobalt Molybdenum Nitride on Self-standing Porous Copper Foam

Hydrogen is an ideal energy carrier, owning to high energy density and zero pollution emission. Hydrogen generation in an alkaline environment is desirable but challenging. A few electrocatalysts have been reported for alkaline hydrogen evolution reaction (HER), but are generally suffered from large over potentials and short durability. Herein, we constructed a self-standing ternary cobalt molybdenum nitride catalyst on copper foam using a simple hydrothermal method and treated under a H2 atmosphere subsequently. Remarkably, the CoN/Mo2N/Cu catalyst exhibits ultralow overpotentials of only 18 mV and 68 mV at current densities of 10 mA cm−2 and 100 mA cm−2 for HER in 1.0 M KOH, respectively. In addition, the ternary catalyst achieves superior durability for more than 100 h at the current density of 20 mA cm−2 without evident deterioration, indicating that the catalyst has an encouraging industrial perspective.

Thermal Stability of Potassium-Promoted Cobalt Molybdenum Nitride Catalysts for Ammonia Synthesis

The application of cobalt molybdenum nitrides as ammonia synthesis catalysts requires further development of the optimal promoter system, which enhances not only the activity but also the stability of the catalysts. To do so, elucidating the influence of the addition of alkali metals on the structural properties of the catalysts is essential. In this study, potassium-promoted cobalt molybdenum nitrides were synthesized by impregnation of the precursor CoMoO4·3/4H2O with aqueous KNO3 solution followed by ammonolysis. The catalysts were characterized with the use of XRD and BET methods, under two conditions: as obtained and after the thermal stability test. The catalytic activity in the synthesis of ammonia was examined at 450 °C, under 10 MPa. The thermal stability test was carried out by heating at 650 °C in the same apparatus. As a result of ammonolysis, mixtures of two phases: Co3Mo3N and Co2Mo3N were obtained. The phase concentrations were affected by potassium admixture. The catalytical activity increased for the most active catalyst by approximately 50% compared to non-promoted cobalt molybdenum nitrides. The thermal stability test resulted in a loss of activity, on average, of 30%. Deactivation was caused by the collapse of the porous structure, which is attributed to the conversion of the Co2Mo3N phase to the Co3Mo3N phase.

Highly Efficient Hydrogen Evolution in Alkaline Medium by Ternary Cobalt Molybdenum Nitride on Self-Standing Porous Copper Foam

Highly Efficient Hydrogen Evolution in Alkaline Medium by Ternary Cobalt Molybdenum Nitride on Self-Standing Porous Copper Foam

Enhancing Ammonia Catalytic Production Over Spatially Confined Cobalt Molybdenum Nitride Nanoparticles in Sba-15

Enhancing Ammonia Catalytic Production Over Spatially Confined Cobalt Molybdenum Nitride Nanoparticles in Sba-15

Sliver nanoparticles decorated Co-Mo nitride for efficient water splitting

Designing highly active and robust bifunctional electrocatalysts toward efficient overall water splitting using for novel renewable energy storage and conversion systems is still a challenging task. Here, self-supported bimetallic cobalt-molybdenum nitride with silver nanoparticles decoration (Co-Mo-N@Ag) growth in situ on carbon paper was rationally designed and fabricated for overall water splitting in alkaline media. By virtue of the admirable compositional and structural advantages of exposed enough active sites, regulated favorable electronic structure, and engineered powerful interface synergy effect, the Co-Mo-N@Ag electrode exhibits superior electrocatalytic performance in 1 M KOH. In the details, an excellent oxygen evolution reaction (OER) activity with an extremely low overpotential of 234 mV at 10 mA cm−2 and a small Tafel slope of 54 mV dec-1, as well as a remarkable hydrogen evolution reaction (HER) activity with a low overpotential of 90 mV at 10 mA cm−2 and Tafel slope of 73 mV dec-1 were acquired by Co-Mo-N@Ag. As a result, it takes a low voltage of 1.56 V to reach 10 mA cm−2 in alkaline overall water splitting. This work presents the heterogeneous interfacial structure decorated by silver and provides a feasible method to increase the OER and HER activity of metal nitrides.

Bimetallic Co-Mo nitride nanosheet arrays as high-performance bifunctional electrocatalysts for overall water splitting

Developing non-precious metal electrocatalysts with high activity and stability are of great significance to achieve overall water splitting. In this work, cobalt-molybdenum nitride nanosheet arrays grown on Ni foam (CoMoNx NSAs/NF) were prepared via a facile hydrothermal and nitridation process. The resulting CoMoNx NSAs/NF not only has a specific large surface area and provides more active sites but also possesses good electrical conductivity, contributing to the fast reaction kinetics. Furthermore, the synergistic effect between Co2N and Mo2N cooperatively enhance the charge transfer, thus further improving the electrocatalytic activity. Benefiting from these merits, the optimal CoMoNx-500 NSAs/NF exhibits excellent activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with overpotentials of 91 and 231 mV at the current density of 10 mA cm−2, respectively. Moreover, the CoMoNx-500 NSAs/NF||CoMoNx-500 NSAs/NF couple requires a low cell voltage of 1.55 V at the current density of 10 mA cm−2, which is much superior to many other reported transition metal nitrides catalysts. This present work provides a reference for the design of bimetallic nitrides with superior electrocatalytic performance foroverall water splitting.

Flexible Co-Mo-N/Au Electrodes with a Hierarchical Nanoporous Architecture as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

Designing highly active and robust electrocatalysts for oxygen evolution reaction (OER) is crucial for many renewable energy storage and conversion devices. Here, self-supported monolithic hybrid electrodes that are composed of bimetallic cobalt-molybdenum nitride nanosheets vertically aligned on 3D and bicontinuous nanoporous gold (NP Au/CoMoNx ) are reported as highly efficient electrocatalysts to boost the sluggish reaction kinetics of water oxidation in alkaline media. By virtue of the constituent CoMoNx nanosheets having large accessible CoMoOx surface with remarkably enhanced electrocatalytic activity and the nanoporous Au skeleton facilitating electron transfer and mass transport, the NP Au/CoMoNx electrode exhibits superior OER electrocatalysis in 1 m KOH, with low onset overpotential (166 mV) and Tafel slope (46 mV dec-1 ). It only takes a low overpotential of 370 mV to reach ultrahigh current density of 1156 mA cm-2 , ≈140-fold higher than free CoMoNx nanosheets. The electrocatalytic performance makes it an attractive candidate as the OER catalyst in the water electrolysis.

Impact of morphology on the oxygen evolution reaction of 3D hollow Cobalt-Molybdenum Nitride

The oxygen evolution reaction (OER) is an essential process for water electrolysis and to realize the scalability of renewable energy sources. In this work, a strategy is developed to fabricate anisotropic metallic Cobalt-Molybdenum Nitride materials combining hollow 3D structures and 2D nanosheets which result highly active OER electrocatalysts. The sample structure and morphology is investigated to derive its formation process following the synthesis strategy relying on the ligand-metal interactions of metal-organic framework (ZIF-67 and Mo-aMOF). Three different sample morphologies with large specific surface areas are obtained by changing the water and 2-methylimidazole contents. After ammonification in NH3, the morphologies and the specific surface areas of the samples are preserved. The electronic structure can also be adjusted to regulate electron density of Co and Mo by N-doping. These Co-Mo binary metals offer a viable way for realizing the electronic transfer between the different components, as demonstrated by XPS. Taking advantage from the above features, the as-obtained electrocatalyst exhibits a high catalytic activity and long-term cyclic stability for OER with low overpotential (η10 is 294 mV).

Chromium-modified cobalt molybdenum nitrides as catalysts for ammonia synthesis

AbstractThe influence of chromium compounds on the properties of cobalt molybdenum nitrides was studied. CoMoO4 obtained by precipitation from cobalt and molybdenum salts was modified by the addition of chromium(III) nitrate. A mixture of cobalt-molybdenum nitrides, Co2Mo3N and Co3Mo3N, was formed by ammonolysis of modified CoMoO4. The concentration of Co2Mo3N decreases with increasing chromium content. The specific surface area of cobalt molybdenum nitrides consisting of 2 wt% of Cr atoms increased by 50% in comparison to pure cobalt molybdenum nitrides. The catalytic activity of obtained catalysts in ammonia synthesis process decreases with rising of chromium concentration.

Thermal stability of catalyst for ammonia synthesis based on cobalt molybdenum nitrides

The formation and stability of an ammonia synthesis catalyst, based on cobalt molybdenum nitrides, were studied. The activation process of the catalyst was examined by in situ X-ray diffractometry. The thermal stability of obtained active phase of the catalyst was tested at 700 °C under ammonia atmosphere, N2/H2 mixture and under pure hydrogen. The presence of Co2Mo3N and Co3Mo3N phases in the catalyst was confirmed. The phase composition was stable in a long-term test performed under nitrogen/hydrogen atmosphere. Co3Mo3N phase decomposed into Co6Mo6N after exposure to pure hydrogen.

Cobalt molybdenum nitrides co-promoted by chromium and potassium as catalysts for ammonia synthesis

Chromium and potassium compounds were added to the ammonia synthesis catalyst based on cobalt molybdenum nitrides. A better developed porous structure was obtained together with the increase of the catalytic activity. In comparison to the non-promoted catalyst, the total surface area and the catalytic activity increased more than 50%. The behavior of the system is discussed in light of the double-layer model of the catalyst surface.

DFT-D3 Study of Molecular N2 and H2 Activation on Co3Mo3N Surfaces

Cobalt molybdenum nitride (Co3Mo3N) is one of the most active catalysts for ammonia synthesis, although the atomistic details of the reaction mechanism are currently unknown. We present a dispersion-corrected (D3) DFT study of the adsorption and activation of molecular nitrogen and hydrogen on Co3Mo3N-(111) surfaces to identify possible activation sites for ammonia synthesis. H2 was found to adsorb both molecularly on the Mo3N framework and dissociatively on Co8 clusters or Mo3 clusters that were exposed due to N-vacancies. We find that there are two possible activation sites for N2 where both N2 and H2 can coadsorb. The first is a Mo3 triangular cluster that resides at 3f nitrogen vacancies, and the second is a surface cavity where N2 is activated by a Co8 cluster, the second being a more efficient activation site. N2 was found to adsorb in three adsorption configurations: side-on, end-on, and an unusual tilt end-on (155°) configuration, and the existence of these three adsorption configurations is expla...

Structure and magnetic properties of chromium doped cobalt molybdenum nitrides

Four nanocomposites containing mixed phases of Co3Mo3N and Co2Mo3N doped with chromium have been prepared. A linear fit is found for relation between Co2Mo3N and chromium concentrations. The magnetization in ZFC and FC modes at different temperatures (2–300K) and in applied magnetic fields (up to 70kOe) have been investigated. It has been detected that many magnetic characteristics of the studied four nanocomposites correlate not with the chromium concentration but with nanocrystallite sizes. The obtained results were interpreted in terms of magnetic core-shell model of a nanoparticle involving paramagnetic core with two magnetic sublattices and a ferromagnetic shell related to chromium doping.

Alloyed Co–Mo Nitride as High-Performance Electrocatalyst for Oxygen Reduction in Acidic Medium

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of fuel cells. Herein, we report an alloyed Co–Mo nitride electrocatalyst supported on nitrogen-doped carbon nanocages (NCNCs) which combines the merits of cobalt nitride and molybdenum nitride, showing high activity comparable to that of cobalt nitride and progressively enhanced stability with the increase in the Mo ratio. The typical Co0.5Mo0.5Ny/NCNCs catalyst demonstrates excellent ORR performance in acidic medium with a high onset potential of 808 mV vs RHE, superior stability (>80% retention after 100 h of continuous testing in 0.5 mol L–1 H2SO4), a dominant four-electron catalytic process, and good immunity to methanol crossover. Together with the convenient and scalable preparation as well as the low cost, the alloyed Co–Mo nitride electrocatalyst shows great potential in application for fuel cells. This study also suggests a promising strategy to d...