Search Results (14)

The rapid growth in population and industrialization have significantly increased global energy demand, placing immense pressure on finite and environmentally harmful conventional fossil fuel-based energy sources. In this context, the development of hybrid electrocatalysts presents a crucial solution for energy conversion and storage, addressing environmental challenges while meeting rising energy needs. In this study, the fabrication of a novel bifunctional catalyst, copper nickel aluminum spinel (Cu_0.5Ni_0.5Al₂O₄) supported on graphitic carbon nitride (GCN), using a solid-state synthesis process is reported. Because of its effective interface design and spinel cubic structure, the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, as synthesized, performs exceptionally well in electrochemical energy conversion, such as the oxygen evolution reaction (OER), the hydrogen evolution reaction (HER), and energy storage. In particular, compared to noble metals, Pt/C- and IrO₂-based water-splitting cells require higher voltages (1.70 V), while for the Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposite, a voltage of 1.49 V is sufficient to generate a current density of 10 mA cm⁻² in an alkaline solution. When used as supercapacitor electrode materials, Cu_0.5Ni_0.5Al₂O₄/GCN nanocomposites show a specific capacitance of 1290 F g⁻¹ at a current density of 1 A g⁻¹ and maintain a specific capacitance of 609 F g⁻¹ even at a higher current density of 5 A g⁻¹, suggesting exceptional rate performance and charge storage capacity. The electrode’s exceptional capacitive properties were further confirmed through the determination of the roughness factor (Rf), which represents surface heterogeneity and active area enhancement, with a value of 345.5. These distinctive characteristics render the Cu_0.5Ni_0.5Al₂O₄/GCN composite a compelling alternative to fossil fuels in the ongoing quest for a viable replacement. Undoubtedly, the creation of the Cu_0.5Ni_0.5Al₂O₄/GCN composite represents a significant breakthrough in addressing the energy crisis and environmental concerns. Owing to its unique composition and electrocatalytic characteristics, it is considered a feasible choice in the pursuit of ecologically sustainable alternatives to fossil fuels. Full article

Noble metals are still in high demand for exhaust control catalysts in mobile sources. Designing highly efficient and less costly catalysts for soot purification from engine emissions is a challenge. Herein, the Ni-Co spinel oxide catalyst made of earth-abundant elements was synthesized by a precipitation method. Based on the test results of powder X-ray diffraction (XRD), N₂ adsorption–desorption experiments, the temperature-programmed oxidation of soot (soot-TPO), the temperature-programmed oxidation of NO (NO-TPO), the temperature-programmed reduction in H₂ (H₂-TPR), and the advantages of Ni-Co synergistic catalysts relative to pure NiO and Co₃O₄ oxides were systematically investigated. The NiCo₂O₄ catalyst exhibits excellent catalytic performance and stability during soot oxidation compared with NiO and Co₃O₄ catalysts, i.e., its T₁₀, T₅₀, T₉₀ and S_CO2^m are 316, 356, 388 °C and 99.95%, respectively. The mechanism of the Ni-Co synergy effect for boosting soot oxidation on the spinel oxide catalyst is proposed according to the experimental results of in situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) and the theoretical knowledge of coordination chemistry of metal–NO. This study lays a good foundation for exhaust purification by non-noble metal catalysts for pollution control and sustainable environmental practices. Full article

Noble metals have become a research hotspot for the oxidation of light alkanes due to their low ignition temperature and easy activation of C-H; however, sintering and a high price limit their industrial applications. The preparation of effective and low-noble-metal catalysts still presents profound challenges. Herein, we describe how a Ru@CoMn₂O₄ spinel catalyst was synthesized via Ru in situ doping to promote the activity of propane oxidation. Ru@CoMn₂O₄ exhibited much higher catalytic activity than CoMn₂O₄, achieving 90% propane conversion at 217 °C. H₂-TPR, O₂-TPD, and XPS were used to evaluate the catalyst adsorption/lattice oxygen activity and the adsorption and catalytic oxidation capacity of propane. It could be concluded that Ru promoted synergistic interactions between cobalt and manganese, leading to electron transfer from the highly electronegative Ru to Co²⁺ and Mn³⁺. Compared with CoMn₂O₄, 0.1% Ru@CoMn₂O₄, with a higher quantity of lattice oxygen and oxygen mobility, possessed a stronger capability of reducibility, which was the main reason for the significant increase in the activity of Ru@CoMn₂O₄. In addition, intermediates of the reaction between adsorbed propane and lattice oxygen on the catalyst were monitored by in situ DRIFTS. This work highlights a new strategy for the design of a low-noble-metal catalyst for the efficient oxidation of propane. Full article

Electrospinning has revolutionized the field of semiconductor metal oxide (SMO) gas sensors, which are pivotal for gas detection. SMOs are known for their high sensitivity, rapid responsiveness, and exceptional selectivity towards various types of gases. When synthesized via electrospinning, they gain unmatched advantages. These include high porosity, large specific surface areas, adjustable morphologies and compositions, and diverse structural designs, improving gas-sensing performance. This review explores the application of variously structured and composed SMOs prepared by electrospinning in gas sensors. It highlights strategies to augment gas-sensing performance, such as noble metal modification and doping with transition metals, rare earth elements, and metal cations, all contributing to heightened sensitivity and selectivity. We also look at the fabrication of composite SMOs with polymers or carbon nanofibers, which addresses the challenge of high operating temperatures. Furthermore, this review discusses the advantages of hierarchical and core-shell structures. The use of spinel and perovskite structures is also explored for their unique chemical compositions and crystal structure. These structures are useful for high sensitivity and selectivity towards specific gases. These methodologies emphasize the critical role of innovative material integration and structural design in achieving high-performance gas sensors, pointing toward future research directions in this rapidly evolving field. Full article

Low-cost, sustainable hydrogen production requires noble metal-free electrocatalysts for water splitting. In this study, we prepared zeolitic imidazolate frameworks (ZIF) decorated with CoFe₂O₄ spinel nanoparticles as active catalysts for oxygen evolution reaction (OER). The CoFe₂O₄ nanoparticles were synthesized by converting agricultural bio-waste (potato peel extract) into economically valuable electrode materials. The biogenic CoFe₂O₄ composite showed an overpotential of 370 mV at a current density of 10 mA cm⁻² and a low Tafel slope of 283 mV dec⁻¹, whereas the ZIF@CoFe₂O₄ composite prepared using an in situ hydrothermal method showed an overpotential of 105 mV at 10 mA cm⁻² and a low Tafel slope of 43 mV dec⁻¹ in a 1 M KOH medium. The results demonstrated an exciting prospect of high-performance noble metal-free electrocatalysts for low-cost, high-efficiency, and sustainable hydrogen production. Full article

Electrocatalytic water splitting is a crucial area in sustainable energy development, and the development of highly efficient bifunctional catalysts that exhibit activity toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance. Co₃O₄ is a promising candidate catalyst, owing to the variable valence of Co, which can be exploited to enhance the bifunctional catalytic activity of HER and OER through rational adjustments of the electronic structure of Co atoms. In this study, we employed a plasma-etching strategy in combination with an in situ filling of heteroatoms to etch the surface of Co₃O₄, creating abundant oxygen vacancies, while simultaneously filling them with nitrogen and sulfur heteroatoms. The resulting N/S-V_O-Co₃O₄ exhibited favorable bifunctional activity for alkaline electrocatalytic water splitting, with significantly enhanced HER and OER catalytic activity compared to pristine Co₃O₄. In an alkaline overall water-splitting simulated electrolytic cell, N/S-V_O-Co₃O₄ || N/S-V_O-Co₃O₄ showed excellent overall water splitting catalytic activity, comparable to noble metal benchmark catalysts Pt/C || IrO₂, and demonstrated superior long-term catalytic stability. Additionally, the combination of in situ Raman spectroscopy with other ex situ characterizations provided further insight into the reasons behind the enhanced catalyst performance achieved through the in situ incorporation of N and S heteroatoms. This study presents a facile strategy for fabricating highly efficient cobalt-based spinel electrocatalysts incorporated with double heteroatoms for alkaline electrocatalytic monolithic water splitting. Full article

Developing an efficient multi-functional electrocatalyst with high efficiency and low cost to replace noble metals is significantly crucial for the industrial water electrolysis process and for producing sustainable green hydrogen (H₂) fuel. Herein, ultrathin CuCo₂S₄ nanosheets assembled into highly open three-dimensional (3D) nanospheres of CuCo₂S₄ (Cu/Co = 33:67) were prepared by a facile one-pot solvothermal approach and utilized as a bifunctional electrocatalyst for efficient overall water splitting. The as-prepared CuCo₂S₄ is characterized structurally and morphologically; the BET surface area of the CuCo₂S₄ (Cu/Co = 33:67) catalyst was found to have a larger specific surface area (21.783 m²g⁻¹) than that of other catalysts with a Cu/Co ratio of 67:33, 50:50, and 20:80. Benefiting from a highly open structure and ultrathin nanosheets with excellent exposure to catalytically active sites, CuCo₂S₄ (Cu/Co = 33:67) is identified as an efficient catalyst for the proton reduction and oxygen evolution reactions in 1 M KOH with an overpotential of 182 and 274 mV at 10 mA cm⁻², respectively. As expected, a low cell voltage of 1.68 V delivers a current density of 10 mA cm⁻². Stability and durability are also greatly enhanced under harsh alkaline conditions. Therefore, this work provides a simple strategy for the rational design of spinel-based transition metal sulfide catalysts for electrocatalysis. Full article

2,4-diaminotoluene (TDA) is one of the most important polyurethane precursors produced in large quantities by the hydrogenation of 2,4-dinitrotoluene using catalysts. Any improvement during the catalysis reaction is therefore of significant importance. Separation of the catalysts by filtration is cumbersome and causes catalyst loss. To solve this problem, we have developed magnetizable, amine functionalized ferrite supported palladium catalysts. Cobalt ferrite (CoFe₂O₄-NH₂), nickel ferrite (NiFe₂O₄-NH₂), and cadmium ferrite (CdFe₂O₄-NH₂) magnetic catalyst supports were produced by a simple coprecipitation/sonochemical method. The nanospheres formed contain only magnetic (spinel) phases and show catalytic activity even without noble metals (palladium, platinum, rhodium, etc.) during the hydrogenation of 2,4-dinitrotoluene, 63% (n/n) conversion is also possible. By decorating the supports with palladium, almost 100% TDA selectivity and yield were ensured by using Pd/CoFe₂O₄-NH₂ and Pd/NiFe₂O₄-NH₂ catalysts. These catalysts possess highly favorable properties for industrial applications, such as easy separation from the reaction medium without loss by means of a magnetic field, enhanced reusability, and good dispersibility in aqueous medium. Contrary to non-functionalized supports, no significant leaching of precious metals could be detected even after four cycles. Full article

We report a new occurrence of preiswerkite, the rare sodium analog of eastonite, the trioctahedral mica, from marble-hosted noble spinel deposits of the Luc Yen district, northern Vietnam. It is found in marble for the first time. The preiswerkite is anhedral and associated with phlogopite, aspidolite, sadanagaite, pargasite, spinel, corundum, dolomite and calcite. The average compositions of preiswerkite is (Na_0.88Ca_0.08K_0.01)_Σ0.97(Mg_2.29Al_0.72Fe_0.04)_Σ3.05)[(Al_1.95Si_2.05)_Σ4.00O₁₀](OH)₂. The compositions of preiswerkite have a narrow range of Mg# values (0.96–0.99) and define a preiswerkite-aspidolite solid-solution series. Compared with other occurrences, the Luc Yen preiswerkite has a low iron content, which attains 0.09 atoms per formula unit (1.53 wt.% FeO). The formation of preiswerkite is favored by the proportion of Mg, Al and Si in the precursor rocks and the increased activity of sodium and H₂O in the fluid phase. Full article

One of the practical efforts in the development of oxygen reduction reaction (ORR) catalysts applicable to fuel cells and metal-air batteries is focused on reducing the cost of the catalysts production. Herein, we have examined the ORR performance of cheap, non-noble metal based catalysts comprised of nanosized mixed Fe-Co spinels deposited on N,S-doped mesoporous carbon support (N,S-MPC). The effect of the chemical and phase composition of the active phase on the selectivity of catalysts in the ORR process in alkaline media was elucidated by changing the iron content. The synthesized materials were thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). Detailed S/TEM/EDX and Raman analysis of the phase composition of the synthesized ORR catalysts revealed that the dominant mixed iron-cobalt spinel is accompanied by minor fractions of bare cobalt and highly dispersed spurious iron oxides (Fe₂O₃ and Fe₃O₄). The contribution of individual phases and their degree of agglomeration on the carbon support directly influence the selectivity of the obtained catalysts. It was found that the mixed iron-cobalt spinel single phase gives rise to significant improvement of the catalyst selectivity towards the desired 4e⁻ reaction pathway, in comparison to the reference bare cobalt spinel, whereas spurious iron oxides play a negative role for the catalyst selectivity. Full article

Developing a highly stable and non-precious, low-cost, bifunctional electrocatalyst is essential for energy storage and energy conversion devices due to the increasing demand from the consumers. Therefore, the fabrication of a bifunctional electrocatalyst is an emerging focus for the promotion and dissemination of energy storage/conversion devices. Spinel and perovskite transition metal oxides have been widely explored as efficient bifunctional electrocatalysts to replace the noble metals in fuel cell and metal-air batteries. In this work, we developed a bifunctional catalyst for oxygen reduction and oxygen evolution reaction (ORR/OER) study using the mechanochemical route coupling of cobalt oxide nano/microspheres and carbon black particles incorporated lanthanum manganite perovskite (LaMnO₃@C-Co₃O₄) composite. It was synthesized through a simple and less-time consuming solid-state ball-milling method. The synthesized LaMnO₃@C-Co₃O₄ composite was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction spectroscopy, and micro-Raman spectroscopy techniques. The electrocatalysis results showed excellent electrochemical activity towards ORR/OER kinetics using LaMnO₃@C-Co₃O₄ catalyst, as compared with Pt/C, bare LaMnO₃@C, and LaMnO₃@C-RuO₂ catalysts. The observed results suggested that the newly developed LaMnO₃@C-Co₃O₄ electrocatalyst can be used as a potential candidate for air-cathodes in fuel cell and metal-air batteries. Full article

Low-energy wet milling was employed to activate commercial CoAl₂O₄ spinel and disperse mono- and multimetallic nanoparticles on its surface. This method yielded efficient Pt,Ni catalysts for soot oxidation in simulated diesel exhaust conditions. The characterization and activity results indicated that although Ni/CoAl₂O₄ was highly active, the presence of Pt was required to obtain a stable Ni(0.25 wt. %),Pt(0.75 wt. %)/CoAl₂O₄ catalyst under the operating conditions of diesel particulate filters, and that hot spots formation must be controlled to avoid the deactivation of the cobalt aluminate. Our work provides important insight for new design strategies to develop high-efficiency low-cost catalysts. Platinum-containing multimetallic nanostructures could efficiently reduce the amount of the costly, but to date non-replaceable, Pt noble metal for a large number of industrially important catalytic processes. Full article

To address aggravating environmental and energy problems, active, efficient, low-cost, and robust electrocatalysts (ECs) are actively pursued as substitutes for the current noble metal ECs. Therefore, in this study, we report the preparation of graphene flakes (GF) doped with S and N using 2-5-dimercapto-1,3,4-thiadiazole (S₃N₂) as precursor followed by the immobilization of cobalt spinel oxide (Co₃O₄) or manganese spinel oxide (Mn₃O₄) nanoparticles through a one-step co-precipitation procedure (Co/S₃N₂–GF and Mn/S₃N₂–GF). Characterization by different physicochemical techniques (Fourier Transform Infrared (FTIR), Raman spectroscopy, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD)) of both composites shows the preservation of the metal oxide spinel structure and further confirms the successful preparation of the envisaged electrocatalysts. Co/S₃N₂–GF composite exhibits the best ORR performance with an onset potential of 0.91 V vs. RHE, a diffusion-limiting current density of −4.50 mA cm⁻² and selectivity for the direct four-electron pathway, matching the results obtained for commercial Pt/C. Moreover, both Co/S₃N₂–GF and Mn/S₃N₂–GF showed excellent tolerance to methanol poisoning and good stability. Full article

Dry reforming of methane (DRM) is an eco-friendly method of syngas production due to the utilization of two main greenhouse gases—methane and carbon dioxide. An industrial application of methane dry reforming requires the use of a catalyst with high activity, stability over a long time, and the ability to catalyze a reaction, leading to the needed a hydrogen/carbon monoxide ratio. Thus, the aim of the study was to investigate the effect of support and noble metal particles on catalytic activity, stability, and selectivity in the dry reforming process. Ni and Ni–Ru based catalysts were prepared via impregnation and precipitation methods on SiO₂, ZrO₂, Al₂O₃, and MgAl₂O₄ supports. The obtained catalysts were characterized using X-ray diffractometry (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), Brunauer–Emmett–Teller (BET) specific surface area, and elemental carbon-hydrogen-nitrogen-sulphur analysis (CHNS) techniques. The catalytic activity was investigated in the carbon dioxide reforming of a methane process at 800 °C. Catalysts supported on commercial Al₂O₃ and spinel MgAl₂O₄ exhibited the highest activity and stability under DRM conditions. The obtained results clearly indicate that differences in catalytic activity result from the dispersion, size of an active metal (AM), and interactions of the AM with the support. It was also found that the addition of ruthenium particles enhanced the methane conversion and shifted the H₂/CO ratio to lower values. Full article