Industrial Chemistry & Materials最新文献

Carbon-supported platinum nanoparticles (Pt/C) are widely used electrocatalysts in proton exchange membrane fuel cell and electrolyzer applications and represent a substantial part of the capital expenditure of these devices. Platinum being a critical raw material, its recovery is critical for the deployment of these technologies. In this contribution, the first step of a recycling protocol, i.e. the leaching of Pt/C, is studied. To avoid the use of concentrated acids and oxidants, the focus of the present study is on the design of an efficient electrochemical protocol. In particular, the values of the upper and lower potential limits have an impact on Pt dissolution efficiency. The upper potential limit should avoid (or at least limit) Pt particles' detachment from the carbon support and the lower potential limit should take into account the competition between the platinum dissolution and the unwanted platinum redeposition. The evolution of the particle morphology and dissolution rate were monitored by coupling a statistical analysis of TEM images and ICP-MS concentration measurements. The cycling potential window was first optimized for a model commercial Pt/C catalyst in a low-chloride concentration electrolyte, leading to a full Pt leaching efficiency (99%). A similar protocol was transferred to more technological objects: MEA aged under realistic conditions. The MEAs were electrochemically treated without any prior GDL separation and the efficiency of the process was demonstrated.

Keywords: MEA recycling; Platinum electrodissolution; Platinum recovery.

The binder adheres to each component of the electrode to maintain the structural integrity and plays an irreplaceable role in a battery despite its low content. Polyvinylidene difluoride (PVDF), as the dominant binder in commercial battery systems (for cathodes), has acceptably balanced properties between chemical/electrochemical stability and adhesive ability. However, in the pursuit of high-specific-energy batteries featuring high mass loading, high voltage, and large volume changes, the PVDF binder is unable to satisfy the versatile electrode demands and extreme operation conditions. Therefore, developing novel binders with task-specific functionality is of urgent need. Herein, we review the recently developed design strategies of functional binders from the insight of molecular design. The functions and failure mechanisms of the binders are elucidated first. Starting from the basic moiety (functional group) of the polymer molecule, how the constituents, molecular structure, and assembly into a supramolecule will affect the properties of the binders, and furthermore the performance of the electrodes, is discussed at length. Finally, we summarize and provide a future outlook on the opportunities and challenges of functional binders towards future high-specific-energy lithium-ion batteries.

Keywords: Functional binders; Molecular design; High-specific-energy electrodes; Lithium-ion batteries.

Control over the pore structure of zeolite is very important, so researchers are trying to regulate the pore structure of zeolite through various methods to endow it with better performance in industrial applications. Here, a confined etching route that could selectively increase the microporous structure of zeolite is developed using ethanol/amine buffer solution. Ethanol is introduced into an aqueous amine solution, where it could decrease the migration rate and concentration of hydroxyl ions which can etch the framework atoms of zeolite to fabricate various porous structures, consequently developing a confined etching route that could selectively increase the microporous structure of zeolite, unlike conventional approaches that generally increase mesoporous and macroporous architectures. In addition, ethanol enhances the solubility of amine in water, and a buffer solution (ethanol/amine) is formed, which is able to release hydroxyl ions continuously. Based on the above confined etching route, a micropore-increased beta crystal is synthesized and when used as a carrier in ZnLaY/beta catalysts, it achieves excellent ethanol conversion of 96.04% and butadiene selectivity of 64.22% in 20 h time-on-stream in an ethanol to butadiene reaction.

Keywords: Ethanol; Confined etching route; Micropore-increased; Beta zeolite; Ethanol to butadiene.

In this study, an ultrasonic assisted natural deep eutectic solvent (DES) was used to extract hydroxytyrosol (HT) from olive leaves. The optimal extraction conditions of the MaPa-4 concentration, extraction time and solid–liquid ratio were obtained by single factor experiments. The formation mechanism of MaPa and its interaction with HT were analyzed by FTIR, ¹H-NMR and density functional theory (DFT) calculation. Then, MaPa-4 and water extracts obtained under the optimal extraction conditions were selected for a series of efficacy tests. MaPa-4 extract demonstrated low cytotoxicity, good biocompatibility, and excellent anti-inflammatory and bacteriostatic properties. Overall, MaPa-4, as an environmentally friendly and efficient solvent, was combined with ultrasound treatment to develop an efficient, green and feasible method to extract HT from olive leaves.

Keywords: Hydroxytyrosol; Deep eutectic solvent; Single-factor experiment; Bacteriostatic; Anti-inflammatory; Antioxidant.

Nickel–iron-oxide catalysts were synthesized by a liquid-phase method, through the oxalate route, and used, as anodes, in an anion exchange membrane electrolyzer. The effect of the heating treatments (performed at 350 °C, 450 °C, and 550 °C) on the structure, composition, particle size, and catalytic activity was analyzed. The morphological features were investigated by transmission electron microscopy (TEM), showing an increased particle size for the catalysts treated at higher temperatures (from ≈4 nm at 350 °C to ≈10 nm at 550 °C). The structure and surface composition were evaluated by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The electrochemical characterization was performed in a 5 cm² single-cell setup. The highest performance was obtained with the sample treated at 450 °C, reaching current density values equal to 3.25 A cm⁻² at 2.2 V. The catalysts' behavior was also compared, under the same conditions, with NiO and IrO₂ commercial catalysts, demonstrating a higher activity of this class of compounds. The time-stability test of ca. 100 h showed a more constant behavior for the catalyst treated at 350 °C.

Keywords: Electrolyser; Nickel–iron oxides; Anion exchange membrane; Oxygen evolution reaction; Calcination temperature.

Research on anion exchange membrane fuel cells (AEMFCs) mainly focuses on the membrane module, and improving its performance has always been the focus of researchers. To create high-performance anion exchange membranes (AEMs), a series of side chain type AEMs were prepared by introducing different proportions of side chains containing anisotropic poly cations with relatively stable piperidinium ring cations and side quaternary ammonium cations as cation groups, using poly(p-terphenyl isatin) (PTI), a main chain polymer without aryl ether bonds. The dense surface of the PTI-N-n series membranes is shown by SEM images; TEM images show that the ion domains are clearly distributed in the membrane, so a continuous ion transport channel is constructed. PTI-N-100 has the highest hydroxide conductivity at 80 °C, reaching 96.83 mS cm⁻¹ due to multiple transport sites. The PTI-N-100 membrane has a peak power density of 180 mW cm⁻² based on the highest ionic conductivity. Therefore, we believe that the introduction of multi-cations contributes to the performance of anion exchange membranes.

Keywords: Multi-cation; Ether-free polymer; Alkaline resistance; Microphase separation.

The ammonia electrooxidation reaction (AmER) has attracted considerable attention due to its potential for hydrogen storage and transportation, as well as its possible application in direct ammonia fuel cells. In the present work, we studied ammonia electrooxidation on carbon-supported Pt/C nanoparticles (NPs) of four average sizes of 1.3, 2.2, 2.8, and 4.2 nm. Carbon-supported Pt NPs with a 20 wt% metal loading were synthesized using the polyol method, and the control of the synthesis solution pH allowed the formation of Pt NPs of different average sizes, which was confirmed by TEM. The onset potential was more negative for the smallest nanoparticles (1.3 nm) compared to those for the larger ones. Pt/C with a mean particle size of 2.2 nm showed better stability while exhibiting comparable activity to the 1.3 nm particles. As revealed by in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), the oxidation products included N–H species, azide ions, and nitrate and nitrite compounds. The N–H stretching peak was observed at about 2800 cm⁻¹ on the Pt surface and in the bulk of the electrolyte. However, the intensity of peaks corresponding to the reaction products was different on the surface of Pt and in the bulk of the electrolyte. NO₂⁻ was mostly observed in the bulk of the electrolyte. In contrast, NO₃⁻ was present on the Pt surface. PM-IRRAS demonstrated that the particle size affected the catalytic activity of Pt/C NPs but not their selectivity. In addition, the PM-IRRAS technique allowed, for the first time, distinguishing both symmetric and asymmetric N–O bonds that were not observed previously using IR spectroscopy during ammonia electrooxidation.

Keywords: Ammonia electrooxidation; Carbon-supported Pt nanoparticle; Catalyst; PM-IRRAS; In situ infrared spectroscopy.

Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media is important for fuel cell applications. Herein, we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8 (ZIF-8) and carbon nanotube (CNT) composite catalysts (ZIF-8@CNT) prepared via high-temperature pyrolysis at 900 °C. The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells (AEMFC). The prepared metal-free (ZNT-900), single-metal-doped (Fe-ZNT-900, Co-ZNT-900) and binary-metal-doped (Fe₁Co₁-ZNT-900, Fe₁Co₂-ZNT-900) catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials. N₂ adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900, while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts. Binary-metal-doped catalysts showed the highest number of ORR-active sites (pyridinic-N, pyrrolic-N, graphitic-N, M–N_x) and exhibited a half-wave potential (E_1/2) of 0.846 and 0.847 V vs. RHE for Fe₁Co₁-ZNT-900 and Fe₁Co₂-ZNT-900, respectively, which surpassed that of the commercial Pt/C catalyst (E_1/2 = 0.834 V). In H₂–O₂ AEMFCs, the Fe₁Co₂-ZNT-900 catalyst delivered a maximum power density (P_max) of 0.171 W cm⁻² and current density at 0.5 V (j_0.5) of 0.326 A cm⁻², which is very close to that of the Pt/C catalyst (P_max = 0.215 W cm⁻² and j_0.5 = 0.359 A cm⁻²). The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.

Keywords: Rotating disk electrode; Anion exchange membrane fuel cell; Zeolitic imidazolate framework; Non-precious metal catalyst; Oxygen reduction reaction.

Single-atom catalysts (SACs) attract significant attention owing to their high catalytic activity, high metal atom utilization efficiency, and well-defined and configurable active sites. However, achieving single-atom dispersion of active metals at high metal loadings remains challenging, limiting the performance of SACs in many practical applications. Herein, we provide a comprehensive review of recent methods developed for synthesizing high-loading SACs, critically exploring their advantages, limitations, and wider applicability. Additionally, we showcase the benefits of high-loading SACs in the oxygen reduction reaction (ORR), water electrolysis, photocatalytic hydrogen production and CO oxidation. Although great recent progress has been made in the synthesis of high loading SACs, simple and universal routes that allowed the pre-programmed preparation of single metal and multi-metal SACs with specific metal coordination need to be discovered.

Keywords: Single atom catalyst; High-loading; Synthesis methods; ORR; Water electrolysis; CO oxidation.

Zeolites-encapsulated metal and metal oxide species are important heterogeneous catalysts. They give performances that steadily outperform traditional supported catalysts in many important reactions and have become a research hotspot. Remarkable achievements have been made with respect to the synthesis, characterization, and performances of metal species (typically metal and metal oxide clusters) confined in zeolites. The development in the strategies for the encapsulation of metal species including post-treatment and in situ synthesis method are introduced and compared. For the characterization of zeolite-encapsulated metal catalysts, the structural and surface properties of metal species are studied by several useful techniques, such as electron microscopy, X-ray absorption (XAS), Fourier transform infrared spectroscopy of CO (FTIR-CO), and chemisorption, which confirm the successful confinement of metal species in zeolites and their unique physiochemical properties. In addition, the encapsulation fraction can be determined by a probe molecular titration reaction. For the catalytic performance of zeolite-encapsulated metal catalysts, the activity, selectivity, and stability are emphasized. Finally, applications of zeolite-encapsulated metal catalysts in hydrogen-related reactions are summarized.

Keywords: Zeolite; Encapsulation; Metal species; Synthesis; Characterization; Catalytic performance.