Search Results (74)

Developing cost-effective, sustainable, and high-performance air electrode catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a significant challenge in the advancement of rechargeable zinc–air batteries (ZABs). Herein, we successfully construct a vacancy-rich heterogeneous perovskite La_0.85Y_0.15Ni_0.7Fe_0.3O₃ (LYNF) hybridized with Co₃O₄ spinel nanoparticles using a simple chemical bath-assisted method. The Co₃O₄ composite LYNF material is systematically evaluated as the bifunctional catalyst for ZABs in the proportion of 25 wt%, 50w t%, and 75 wt% (denoted as LYNF-xCo₃O₄, x = 0.25, 0.5, 0.75). The results confirm an intimate coupling between the perovskite and spinel phases, along with a significant increase in oxygen vacancy concentration. Among the composites, LYNF-0.5Co₃O₄ exhibits the best performance, achieving an ORR onset potential of 0.813 V vs. RHE at −0.1 mA cm⁻² and a lower OER overpotential of 441 mV at 10 mA cm⁻². When applied as the air electrode catalyst in ZABs, LYNF-0.5Co₃O₄ displays the highest discharge voltage and a peak power density of 115 mW cm⁻², representing a 20% improvement over pristine LYNF. The enhanced performance of the LYNF-0.5Co₃O₄ composite is attributed to the accumulation of Co₃O₄ nanoparticles within the LYNF matrix, which introduces numerous electrochemically active sites and facilitates the charge and mass transport during the catalytic process in ZABs. Full article

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

The development of efficient platinum group metal-free (PGM-free) catalysts for the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR) is essential for advancing hydrogen-based energy technologies. In this study, Ni_xMo_100−x composites supported on Carbon Ketjenblack EC-300J (CK) were synthesized via thermal reduction under a controlled Ar/H₂ (95:5) atmosphere to investigate the effect of the Ni/Mo molar ratio on electrocatalytic performance. Structural and morphological analyses by XRD and TEM confirmed the formation of the NiMo alloys and carbide phases with controlled particle size distributions (~18 nm), while BET measurements revealed specific surface areas up to 124.69 m² g⁻¹ for the Pt-loaded samples. Notably, the 3% Pt/Ni₉₀Mo₁₀-CK catalyst exhibited outstanding bifunctional activity in a half-cell configuration, achieving an overpotential of 65.2 mV and a Tafel slope of 41.6 mV dec⁻¹ for the HER, and a Tafel slope of 32.9 mV dec⁻¹ with an exchange current density of 1.03 mA cm⁻² for the HOR. These results demonstrate that compositional tuning and minimal Pt incorporation synergistically enhance the catalytic efficiency, providing a promising platform for next-generation hydrogen electrocatalysts. Full article

Crystalline–amorphous core–shell-like heterostructures have attracted considerable attention in electrocatalysis due to their unique electronic and structural properties; however, tuning the surface composition of the amorphous shell remains a major challenge. In this work, we report a simple, low-cost, one-pot hydrazine-assisted chemical deposition method for synthesizing a series of Co-doped Ni@Ni(OH)₂ catalysts with a crystalline Ni core and an amorphous Ni(OH)₂ shell. Among the prepared catalysts, the sample containing 10 wt.% cobalt (denoted as b-Co-doped Ni@Ni(OH)₂) exhibited the highest electrocatalytic activity toward both the oxygen evolution reaction (OER) and the urea oxidation reaction (UOR). In 1.0 M KOH, the b-Co-doped Ni@Ni(OH)₂ catalyst achieved a 40 mV lower overpotential at 50 mA·cm⁻² compared to undoped Ni@Ni(OH)₂ for the OER. For the UOR in 0.33 M urea/1.0 M KOH, it delivered approximately twice the anodic current density relative to the undoped sample, along with improved reaction kinetics as evidenced by a Tafel slope of 70.7 mV·dec⁻¹. This performance enhancement is attributed to the optimized core–shell-like architecture, cobalt doping-induced electronic modulation, increased electrochemically active surface area, and improved charge transfer efficiency. Overall, this study demonstrates a promising and scalable strategy for designing advanced Ni-based bifunctional catalysts for sustainable energy conversion and wastewater treatment applications. Full article

In this study, a Brönsted–Lewis bifunctional acidic catalyst PW/UiO/CNTs-OH was synthesized via the hydrothermal method. The parameters for the esterification reaction of oleic acid with methanol catalyzed by PW/UiO/CNTs-OH were optimized using central composite design-response surface methodology (CCD-RSM). A biodiesel yield of 92.9% was achieved under the optimized conditions, retaining 82.3% biodiesel yield after four catalytic cycles. The enhanced catalytic performance of PW/UiO/CNTs-OH can be attributed as follows: the [Zr₆O₄(OH)₄]¹²⁺ anchored on the surface of multi-walled carbon nanotubes (MWCNTs) can serve as nucleation sites for UiO-66, not only encapsulating H₃[P(W₃O₁₀)₄] (HPW) but also reversing the quadrupole moment of MWCNTs to generate Lewis acid sites. In addition, introduction of HPW during synthesis of UiO-66 decreases the solution pH, inducing the protonation of p-phthalic acid (PTA) to disrupt the coordination with the [Zr₆O₄(OH)₄] cluster, thereby creating an unsaturated Zr⁴⁺ site with electron pair-accepting capability, which generates Lewis acid sites. EIS analysis revealed that PW/UiO/CNTs-OH has higher electron migration efficiency than UiO-66 and PW/UiO. Furthermore, NH₃-TPD and Py-IR analyses showed that PW/UiO/CNTs-OH possessed high densities of Lewis acidic sites of 83.69 μmol/g and Brönsted acidic sites of 9.98 μmol/g. Full article

The conversion of CO₂ into light olefins over bifunctional catalysts is a promising route for producing high-value-added products. This approach not only mitigates excessive CO₂ emissions but also reduces the chemical industry’s reliance on fossil fuels. Among bifunctional catalysts, ZnZrO_x is widely used due to its favorable oxide composition. In this work, ZnZrO_x solid solution was synthesized by calcining an MOF precursor, resulting in a large specific surface area and a small particle size. Characterization studies revealed that ZnZrO_x prepared via MOF calcination exhibited an enhanced CO₂ activation and H₂ dissociation capacity compared to that synthesized using the co-precipitation method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ adsorption on ZnZrO_x led to the formation of carbonate species, while HCOO* and CH₃O* intermediates were generated upon exposure to the reaction gas. When ZnZrO_x was combined with SAPO-34 molecular sieves under reaction conditions of 380 °C, 3 MPa, and 6000 mL·g_cat⁻¹·h⁻¹, the CO₂ conversion reached 34.37%, with a light olefin yield of 15.13%, demonstrating a superior catalytic performance compared to that of the co-precipitation method. Full article

In the present study, self-assembled hierarchical CoMn-LDH, CoMn@CuZnS, and CoMn@CuZnFeS heterostructured composites were synthesized for bifunctional applications. As an electrode for a supercapacitor, CoMn-LDH demonstrated superior areal and specific capacitance of 5.323 F cm⁻² (279.49 mAh/g) at 4 mA cm⁻², comparable to or even higher than other LDHs. The assembled AC//CoMn-LDH hybrid supercapacitor device further demonstrated better stability with 63% original capacitance over 20,000 cycles. Later, as a catalyst, CoMn-LDH, CoMn@CuZnS, and CoMn@CuZnFeS electrodes revealed better performance, with overpotentials of 340, 350, and 366 and −199, −215, and −222 mV to attain 10 mA cm⁻² of current density for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Moreover, for CoMn-LDH, small Tafel slopes of 102 and 128 mV/dec were noticed for OER and HER with good stability compared to heterostructured electrodes. Full article

To address the detrimental effects of the residue of catalysts on the tribological performances of ester lubricants, a novel and efficient bi-functional ionic liquid 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methylimidazole di(2-ethylhexyl) phosphate ([(BHT-1)MIM][DEHP]) was prepared. The catalyst not only facilitates the synthesis of pentaerythritol tetra-hexanoate (PETH) through the catalytic esterification reaction—achieving up to 96% conversion with a 94% yield—but also enhances the tribological performance of ester oil PETH when used as a lubricant additive. The tribological property has been improved remarkably: the mean friction coefficient for PETH + [(BHT-1)MIM][DEHP] is notably lower, at 0.110, compared to the PETH, which has a coefficient of 0.180. Meanwhile, the wear scar diameter of the steel ball, when lubricated with PETH + [(BHT-1)MIM][DEHP], is notably smaller than that of a steel ball lubricated solely with PETH. Especially, the reduction in the wear volume at 100 °C is up to 81.46% compared with the base oil PETH. [(BHT-1)MIM][DEHP], PETH + [(BHT-1)MIM][DEHP], and the worn track of the upper running ball and lower disc were systematically characterized by using Nuclear Magnetic Resonance (NMR) spectra, a Fourier Transform Infrared Spectrometer (FT-IR), a field emission scanning electron microscope (FESEM), Thermal gravity analysis (TG), X-ray photoelectron spectroscopy (XPS), and an optical microscope (OM). The wear mechanism of the tailored lubricant oil was discussed in terms of the chemical composition of the worn surface. Full article

This paper studies the catalytic hydrogenation reduction of lignin-derived phenolic compounds, such as catechol, guaiacol (O-methoxyphenol), phenol, P-methylphenol, O-ethylphenol, O-ethoxyphenol, etc. The reaction system focuses on the catalytic performance of hydrodeoxygenation reactions involving the phenolic derivatives of the lignin depolymerization products catechol and guaiacol. A series of Al₂O₃-TiO₂ composite oxide supports with different Al/Ti ratios were prepared by a co-precipitation method, and a 5% Pd/Al₂O₃-TiO₂ bifunctional catalyst was prepared by an impregnation method and characterized with XRD, SEM, BET, NH₃-TPD, etc. Among these, the Pd/Al₂Ti₁ catalyst had the most excellent catalytic performance. At 100 °C and 2 MPa hydrogen pressure, the conversion of catechol was as high as 100%, and at 100 °C and 5 MPa hydrogen pressure, the conversion of guaiacol reached 90%. Full article

The development of effective bifunctional catalysts demonstrating high performance in both photocatalytic hydrogen evolution and selective hydrogenation of unsaturated compounds is of great interest for photocatalytic transfer hydrogenation. In this work, TiO₂ and Pd@TiO₂ catalysts were studied in two separate processes: photocatalytic H₂ evolution and conventional hydrogenation reactions. Photocatalytic properties of titanium dioxide synthesized by a simple precipitation method were compared with those of commercial ones. Commercial anatase with a lower agglomeration degree showed better activity in H₂ evolution. Further modification of the commercial anatase with Pd resulted in increasing its activity, achieving an H₂ evolution rate of 760 μmol/h g_cat. The Pd catalysts supported on different TiO₂ samples were tested in hydrogenation of acetylenic compounds. The activity of the Pd@TiO₂ catalysts was found to be dependent on the photocatalytic properties of TiO₂ supports. XPS studies of Pd catalysts indicated that commercial anatase with better photocatalytic properties provided easier reduction of Pd²⁺ to active Pd⁰ particles. The Pd catalyst supported on commercial anatase demonstrated the highest activity in the hydrogenation process. The W_C≡C rate achieved 2.6 × 10⁻⁶, 9.0 × 10⁻⁶ and 35.7 × 10⁻⁶ mol/s for hydrogenation of 2-hexyne-1-ol, 5-hexyne-1-ol and 2-hexyne, respectively. The selectivity of the catalyst to target olefinic compounds was 94–96%. In addition, the hydrogenation rate was found to be significantly affected by reaction conditions such as hydrogen concentration and solvent composition. The W_C≡C rate decreased linearly with decreasing hydrogen concentration in a H₂:He gas mixture (30–100 vol%). Performing the reaction in 0.10 M NaOH ethanolic solution resulted in increasing the W_C≡C rate and selectivity of the process. The Pd catalyst was reused in an alkali medium (NaOH in ethanol) for 35 runs without significant degradation in its catalytic activity. Thus, the results obtained in this work can be useful in photocatalytic transfer hydrogenation. Full article

The scalable fabrication of cost-efficient bifunctional catalysts with enhanced hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance plays a significant role in overall water splitting in hydrogen production fields. MoSe₂ is considered to be one of the most promising candidates because of its low cost and high catalytic activity. Herein, hierarchical nitrogen-doped carbon networks were constructed to enhance the catalytic activity of the MoSe₂-based materials by scalable free-drying combined with an in situ selenization strategy. The rationally designed carbonaceous network-encapsulated MoSe₂ composite (MoSe₂/NC) endows a continuous honeycomb-like structure. When utilized as a bifunctional electrocatalyst for both HER and OER, the MoSe₂/NC electrode exhibits excellent electrochemical performance. Significantly, the MoSe₂/NC‖MoSe₂/NC cells require a mere 1.5 V to reach a current density of 10 mA cm⁻² for overall water splitting in 1 M KOH. Ex situ characterizations and electrochemical kinetic analysis reveal that the superior catalytic performance of the MoSe₂/NC composite is mainly attributed to fast electron and ion transportation and good structural stability, which is derived from the abundant active sites and excellent structural flexibility of the honeycomb-like carbon network. This work offers a promising pathway to the scalable fabrication of advanced non-noble bifunctional electrodes for highly efficient hydrogen evolution. Full article

To address issues of global energy sustainability, it is essential to develop highly efficient bifunctional transition metal-based electrocatalysts to accelerate the kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, the heterogeneous molybdenum and vanadium codoped cobalt carbonate nanosheets loaded on nickel foam (VMoCoCOx@NF) are fabricated by facile hydrothermal deposition. Firstly, the mole ratio of V/Mo/Co in the composite is optimized by response surface methodology (RSM). When the optimized composite serves as a bifunctional catalyst, the water-splitting current density achieves 10 mA cm⁻² and 100 mA cm⁻² at cell voltages of 1.54 V and 1.61 V in a 1.0 M KOH electrolyte with robust stability. Furthermore, characterization is carried out using field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations reveal that the fabricated VMoCoCOx@NF catalyst synergistically decreases the Gibbs free energy of hydrogen and oxygen-containing intermediates, thus accelerating OER/HER catalytic kinetics. Benefiting from the concerted advantages of porous NF substrates and clustered VMoCoCOx nanosheets, the fabricated catalyst exhibits superior electrocatalytic performance. This work presents a novel approach to developing transition metal catalysts for overall water splitting. Full article

New bifunctional cobalt catalysts for combined Fischer–Tropsch synthesis and hydroprocessing of hydrocarbons containing Pt were developed. To prepare catalysts in the form of a composite mixture, the FT synthesis catalyst Co-Al₂O₃/SiO₂ and ZSM-5 zeolite in the H-form were used as metal and acid components, respectively, with boehmite as a binder. The catalysts were characterized by various methods, such as XRD using synchrotron radiation, SEM, EDS, TEM and TPR. The effect of the Pt introduction method on the particle size and conditions for cobalt reduction was studied. The testing of catalysts in Fischer–Tropsch synthesis was carried out at a pressure of 2.0 MPa, a temperature of 240 and 250 °C, an H₂/CO ratio of 2 and a synthesis gas volumetric velocity of 1000 h⁻¹. It is shown that the method of introducing a hydrogenating metal by adjusting the nano-sized spatial structure of the catalyst determined the activity in the synthesis and group and fractional composition of the resulting products. It is established that the presence of Pt intensified the processes of synthesis and hydrogenation, including isomeric products, and reduced the content of unsaturated hydrocarbons. The application of Pt by impregnation onto the surface of the metal component of the catalysts provided the highest productivity for C₅₊ hydrocarbons, and for the acidic component, it enabled maximum cracking and isomerizing abilities. Full article

Hydrogen, one of the most promising forms of new energy sources, due to its high energy density, low emissions, and potential to decarbonize various sectors, has attracted significant research attention. It is known that electrocatalytic hydrogen production is one of the most widely investigated research directions due to its high efficiency in the conversion of electricity to H₂ gas. However, given the limited reserves and high cost of precious metals, the search for non-precious metal-based catalysts has been widely explored, for example, transition metal phosphides, oxides, and sulfides. Despite this interest, a detailed survey unveils that the surface and internal structures of the alternative catalysts, including their surface reconstruction, composition, and electronic structure, are poorly studied. As a result, a disconnection in the structure–property relationship severely hinders the rational design of efficient and reliable non-precious metal-based catalysts. In this review, by focusing on Ni₅P₄, a bifunctional catalyst for water splitting, we systematically summarize the material motifs pertaining to the different synthetic methods, surface characteristics, and hydrolysis properties. It is believed that a cascaded correlation may provide insights toward understanding the fundamental catalytic mechanism and design of robust alternative catalysts for hydrogen production. Full article

Recently, perovskite (ABO₃) nanomaterials have been widely explored as a class of versatile electrocatalysts for oxygen evolution reactions (OER) due to their remarkable compositional flexibility and structural tunability, but their poor electrical conductivity hinders hydrogen evolution reaction (HER) activity and further limits the large-scale application of perovskite oxide in overall water splitting (OWS). In this study, hollow-nanotube-structure La_xCo_0.4Fe_0.6O_3−δ (x = 1.0, 0.9, and 0.8) perovskites with superior HER/OER activity were synthesized on nickel-iron alloy foam (denoted La_xCoFe/NFF) using hydrothermal with a subsequent calcination strategy. Among them, La_0.9CoFe/NFF not only exhibited extraordinary HER electrocatalytic performance (160.5 mV@10 mA cm⁻² and 241.0 mV@100 mA cm⁻²) and stability (20 h@10 mA cm⁻²), but also displayed significant OER electrocatalytic activity (234.7 mV@10 mA cm⁻² and 296.1 mV@100 mA cm⁻²) and durability (20 h@10 mA cm⁻²), outperforming many recently reported HER/OER perovskite catalysts. The increase in oxygen vacancies caused by the introduction of La deficiency leads to the expansion of the lattice, which greatly accelerates the HER/OER process of La_0.9CoFe/NFF. Additionally, the naturally porous skeleton can prevent catalysts from aggregating as well as delay the corrosion and dissolution of catalysts in the electrolyte under high applied potentials. Furthermore, the assembled two-electrode configuration, utilizing La_0.9CoFe/NFF (cathode and anode) electrodes, only requires a low cell voltage of 1.573 V at 10 mA cm⁻² for robust alkaline OWS, accompanied by remarkable durability over 20 h. This work provides inspiration for the design and preparation of high-performance and stable bifunctional perovskite electrocatalysts for OWS. Full article