Industrial Chemistry & Materials最新文献

High temperature proton exchange membrane fuel cells (HT-PEMFCs) operating at elevated temperatures above 120 °C take advantage of feasible anode fuels and simplified water/heat management. A high temperature polymer electrolyte membrane (HT-PEM) is the core material for HT-PEMFCs. In this work, a series of phosphoric acid (PA) doped HT-PEMs based on poly(terphenyl piperidine) (PTP) tailored with alkyl groups are synthesized. Five different pendant alkyl groups (including methyl, propyl, pentyl, heptyl and decyl) are grafted onto the piperidine group through the Menshutkin reaction between PTP and alkyl halides. Compared with PTP and methyl grafted PTP (PTP-C1) membranes, the PTP-Cx membranes with long alkyl side chains exhibit improved PA doping contents and conductivities. The optimized pentyl-substituted PTP membrane (PTP-C5) possessed a reasonable PA doping content (202% after immersing in 85 wt% PA at 60 °C), high proton conductivity (96 mS cm⁻¹ at 180 °C) and good tensile strength (4.6 MPa at room temperature). A H₂–air single cell equipped with PTP-C5/PA consequently achieved a high peak power density of 676 mW cm⁻² at 210 °C without any humidification or backpressure. Thus, this work provides a simple method for preparing high-performance HT-PEMs.

Keywords: High temperature polymer electrolyte membrane; Fuel cell; Grafted membrane.

Electrochemical water splitting has been considered a clean and continual way for hydrogen (H₂) production. Direct seawater electrolysis is a potentially attractive technology due to the ample access to seawater and scarce freshwater resources in some regions. However, the presence of impurities (e.g., Cl⁻, Mg²⁺) and the resulting corrosion and side reactions, such as the chloride oxidation reaction (ClOR), makes seawater electrocatalysis more challenging than that of fresh or alkaline water due to competition with the oxygen evolution reaction (OER) at the anode. Consequently, much effort has been devoted to developing approaches to enhance OER performance and suppress the ClOR. In this minireview, we summarize three general strategies for enhancing OER activity and selectivity in seawater electrolysis based on three different concepts: (1) the sole development of robust and high-performance OER catalysts in pure seawater electrolytes, (2) the introduction of additives to seawater electrolytes (e.g., alkalis and/or salts without chloride) to enhance the potential equilibrium gap between the ClOR and OER in combination with regular highly active OER catalysts, and (3) a combination of approaches (1) and (2). Finally, the current challenges and potential opportunities for green H₂ production from seawater electrolysis are briefly presented.

Keywords: Electrochemical seawater splitting; Alkaline seawater electrolysis; Oxygen evolution reaction; Hydrogen production; Electrocatalysts.

Palladium-catalyzed carbonylation is an efficient approach to prepare carbonyl-containing compounds with high atomic economy in synthetic organic chemistry. However, in comparison with aryl halides, carbonylation of alkyl halides is relatively challenging due to the decreased stability of the palladium intermediates. Carbonylation of activated alkyl halides is even more difficult, as nucleophilic substitution reactions with nucleophiles occur more easily with them. In this article, we summarize and discuss recent achievements in palladium-catalyzed carbonylative reactions of activated alkyl halides. The transformations proceed through radical intermediates which are generated in various manners. Under a relatively high pressure of carbon monoxide, the corresponding aliphatic carboxylic acid derivates were effectively prepared with various nucleophiles as the reaction partners. Besides alcohols, amines and organoboron reagents, four-component reactions in combination with alkenes or alkynes were also developed. Case-by-case reaction mechanisms are discussed as well and a personal outlook has also been provided.

Keywords: Carbonyl group; Palladium catalysis; Carbonylation; Activated alkyl halides; Radical intermediates.

Metal patterning from a modified tannic acid (TA-Boc-MA) photoresist and the processes are designed using protection of hydroxyl groups in tannic acid, formulation into a photoresist, an exposure and pattern treatment process, and metallization by electroless Ag deposition with silver ion solution.

Keywords: Tannic acid; Positive photoresist; Metallization method; Metal patterning; Ag pattern.

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MEAs with various cathode Pt loadings were elaborated and aged using a multiple-stressor accelerated stress test (AST) in a segmented PEMFC. The thinnest (lowest Pt loading) cathodes have lower initial activity, owing to larger oxygen reduction reaction hindrance and oxygen transport resistance. Although the lowest cathode Pt loadings initially degrade faster, the overall loss of ECSA at end-of-test is nearly similar whatever the cathode Pt loading, with no local heterogeneities of aging detected along the gas channels. The cathode Pt/C catalyst degrades mostly by Ostwald ripening (which seems more pronounced for lower cathode Pt loading) and nanoparticles agglomeration, owing to superficial carbon functionalization and related Pt crystallite migration: no consequent carbon corrosion is witnessed in this AST. Also, the oxidized Pt²⁺ ions formed by Pt corrosion diffuse/migrate roughly in a similar manner through the membrane for all cathode Pt loadings, and are re-deposited by crossover H₂ close to the cathode|membrane interface. Overall, the mechanisms of Pt/C degradation are not depending on the cathode Pt loading for the chosen AST.

Keywords: Proton exchange membrane fuel cells (PEMFC); Cathode catalyst layer (CL); Platinum loading; Durability.

To develop graphene-based nanomaterials as reliable catalysts for electrochemical energy conversion and storage systems (e.g. PEM fuel cells, metal–air batteries, etc.), it is imperative to critically understand their performance changes and correlated material degradation processes under different operational conditions. In these systems, hydrogen peroxide (H₂O₂) is often an inevitable byproduct of the catalytic oxygen reduction reaction, which can be detrimental to the catalysts, electrodes, and electrolyte materials. Here, we studied how the electrocatalytic performance changes for a heterogeneous nanocatalyst named nitrogen-doped graphene integrated with a metal–organic framework (N-G/MOF) by the effect of H₂O₂, and correlated the degradation process of the catalyst in terms of the changes in elemental compositions, chemical bonds, crystal structures, and morphology. The catalyst samples were treated with five different concentrations of H₂O₂ to emulate the operational conditions and examined to quantify the changes in electrocatalytic performances in an alkaline medium, elemental composition and chemical bonds, crystal structure, and morphology. The electrocatalytic performance considerably declined as the H₂O₂ concentration reached above 0.1 M. The XPS analyses suggest the formation of different oxygen functional groups on the material surface, the breakdown of the material's C–C bonds, and a sharp decline in pyridinic-N functional groups due to gradually harsher H₂O₂ treatments. In higher concentrations, the H₂O₂-derived radicals altered the crystalline and morphological features of the catalyst.

Keywords: Nitrogen-doped graphene-based electrocatalyst; Metal–organic framework; Hydrogen peroxide effect on catalyst; Electrocatalytic performance; Material degradation.

The widespread application of polymer electrolyte membrane water electrolyzers (PEMWEs) remains a tough challenge to date, as they rely on the use of highly scarce iridium (Ir) with insufficient catalytic performance for the oxygen evolution reaction (OER). Therefore, exploring the degradation and activation mechanism of Ir-based catalysts during the OER and searching for highly efficient Ir-based catalysts are essential to achieve large-scale hydrogen production with PEMWEs. This minireview briefly describes the adsorbate evolution mechanism and lattice oxygen oxidation mechanism for Ir-based catalysts to complete the OER process. Then, the valence change of Ir during the OER is discussed to illustrate the origin of the favorable stability of Ir-based catalysts. After that, different modification strategies for IrO₂, such as elemental doping, surface engineering, atom utilization enhancing, and support engineering, are summarized in the hopes of finding some commonalities for improving performance. Finally, the perspectives for the development of Ir-based OER catalysts in PEMWEs are presented.

Keywords: Polymer electrolyte membrane water electrolyzers; Oxygen evolution reaction; Iridium catalysts; Degradation mechanism; Hydrogen production.

In this work, platinum group metal-free (PGM-free) electrocatalysts were synthesized, characterized, and tested for hydrogen evolution reaction (HER). These materials were mono-, bi- and trimetallic Ni-based electrocatalysts with the addition of a second or a third transition metal (TM), such as iron and cobalt. TM–phthalocyanine (TMPc) was used as a metal precursor, mixed with a conductive carbon backbone and subjected to pyrolysis under controlled temperature and atmosphere conditions. Two temperatures of pyrolysis (600 °C and 900 °C) were used. The effect of TM loading in the precursors, different pyrolysis temperatures on the surface chemistry and morphology, and electrocatalytic activity towards HER were evaluated. The increase of NiPc in the initial mixture is beneficial to improving the electrocatalytic activity. The addition of a second and a third metal reflects positively on the HER performance. Interestingly, the pyrolysis temperature influences both the formation and growth of the nanoparticles, and this information is supported by high-resolution transmission electron microscopy (HR-TEM) and light synchrotron X-ray absorption spectroscopy (XAS) measurements.

Keywords: Hydrogen evolution reaction; PGM-free electrocatalyst; Hydrogen production; Ni-based electrocatalyst.

Hydrogen peroxide (H₂O₂) is a green oxidant that has been widely used. The direct synthesis of hydrogen peroxide (DSHP) offers significant advantages in terms of high atomic economy and environmentally friendly effects. However, due to the inevitable side reactions and severe mass transfer limitations, it is still challenging to balance the selectivity and activity for the DSHP. Combining theoretical understanding with the controllable synthesis of nanocatalysts may significantly facilitate the design of “dream catalysts” for the DSHP. In this work, the main factors affecting the reaction performance of catalysts and the active sites of catalysts have been reviewed and discussed in detail. The development and design of catalysts with high efficiency were introduced from three aspects: the catalyst support, active component and atomic impurity. In addition, the coupling of DSHP and other oxidation reactions to realize one-pot in situ oxidation reactions was comprehensively emphasized, which showed essential guiding significance for the future development of H₂O₂.

Keywords: Direct synthesis of H₂O₂; Pd-based catalyst; Selectivity and activity; Catalytic mechanism; In situ oxidation reactions.