Mechanistic Studies for Palladium Catalyzed Copolymerization of Ethylene with Vinyl Ethers

Multivalent Sulfur Vacancy-Rich NiCo2S4@MnO2 Urchin-Like Heterostructures for Ambient Electrochemical N2 Reduction to NH3

Innovative advances in the exploitation of effective electrocatalytic materials for the reduction of nitrogen (N2) to ammonia (NH3) are highly required for the sustainable production of fertilizers and zero-carbon emission fuel. In order to achieve zero-carbon footprints and renewable NH3 production, electrochemical N2 reduction reaction (NRR) provides a favorable energy-saving alternative but it requires more active, efficient, and selective catalysts. In current work, sulfur vacancy (Sv)-rich NiCo2S4@MnO2 heterostructures are efficaciously fabricated via a facile hydrothermal approach followed by heat treatment. The urchin-like Sv-NiCo2S4@MnO2 heterostructures serve as cathodes, which demonstrate an optimal NH3 yield of 57.31 µg h-1 mgcat -1 and Faradaic efficiency of 20.55% at -0.2 V versus reversible hydrogen electrode (RHE) in basic electrolyte owing to the synergistic interactions between Sv-NiCo2S4 and MnO2. Density functional theory (DFT) simulation further verifies that Co-sites of urchin-like Sv-NiCo2S4@MnO2 heterostructures are beneficial to lowering the energy threshold for N2 adsorption and successive protonation. Distinctive micro/nano-architectures exhibit high NRR electrocatalytic activities that might motivate researchers to explore and concentrate on the development of heterostructures for ambient electrocatalytic NH3 generation.

Highly Stretchable Polyurethane Porous Membranes with Adjustable Morphology for Advanced Lithium Metal Batteries

A highly flexible, tunable morphology membrane with excellent thermal stability and ionic conductivity can endow lithium metal batteries with high power density and reduced dendrite growth. Herein, a porous Polyurethane (PU) membrane with an adjustable morphology was prepared by a simple nonsolvent-induced phase separation technique. The precise control of the final morphology of PU membranes can be achieved through appropriate selection of a nonsolvent, resulting a range of pore structures that vary from finger-like voids to sponge-like pores. The implementation of combinatorial DFT and experimental analysis has revealed that spongy PU porous membranes, especially PU-EtOH, show superior electrolyte wettability (472%), high porosity (75%), good mechanical flexibility, robust thermal dimensional stability (above 170 °C), and elevated ionic conductivity (1.38 mS cm-1) in comparison to the polypropylene (PP) separator. The use of PU-EtOH in Li//Li symmetric cell results in a prolonged lifespan of 800 h, surpasing the longevity of PU or PP cells. Moreover, when subjected to a high rate of 5 C, the LiFePO4/Li half-cell with a PU-EtOH porous membrane displayed better cycling performance (115.4 mAh g-1) compared to the PP separator (104.4 mAh g-1). Finally, the prepared PU porous membrane exhibits significant potential for improving the efficiency and safety of LMBs.

Recent Advancements in Mechanistic Studies of Palladium- and Nickel-Catalyzed Ethylene Copolymerization with Polar Monomers

The introduction of polar functional groups into polyolefin chain structures creates opportunities to enhance specific properties, such as adhesion, dyeability, printability, compatibility, thermal stability, and electrical conductivity, which widen the range of potential applications for these modified materials. Transition metal catalysts, especially late transition metals, have proven to be highly effective in copolymerization processes due to their reduced Lewis acidity and electrophilicity. However, when compared to the significant progress and summary of synthetic methods, there is a distinct lack of a comprehensive summary of mechanistic studies pertaining to the catalytic systems involved in ethylene copolymerization catalyzed by palladium and nickel catalysts. In this review, we have provided a comprehensive summary of the latest developments in mechanistic studies of ethylene copolymerization with polar monomers catalyzed by late-transition-metal complexes. Experimental and computational methods were employed to conduct a detailed investigation of these organic and organometallic systems. It is mainly focused on ligand substitution, changes in binding modes, ethylene/polar monomer insertion, chelate opening, and β-H elimination. Factors that control the catalytic activity, molecular weight, comonomer incorporation ratios, and branch content are analyzed, these include steric repulsions between ligands and monomers, electronic effects arising from both ligands and monomers, and so on.

Mechanistic Study on Steric Activity Interplay of Olefin/Polar Monomers for Industrially Selective Late Transition Metal Catalytic Reactions

A significant issue in developing metal-catalyzed plastic polymer materials is obtaining distinctive catalytic characteristics to compete with current plastics in industrial commodities. We performed first-principle DFT calculations on the key insertion steps for industrially important monomers, vinyl fluoride (VF) and 3,3,3-trifluoropropene (TFP), to explain how the ligand substitution patterns affect the complex's polymerization behaviors. Our results indicate that the favorable 2,1-insertion of TFP is caused by less deformation in the catalyst moiety of the complexes in contrast to the 1,2-insertion mode. In contrast to the VF monomer, the additional interaction between the fluorine atoms of 3,3,3-trifluoropropene and the carbons of the catalyst ligands also contributed to favor the 2,1-insertion. It was found that the regioselectivity of the monomer was predominated by the progressive alteration of the catalytic geometry caused by small dihedral angles that were developed after the ligand-monomer interaction. Based on the distribution of the 1,2- and 2,1-insertion products, the activity and selectivity were influenced by the steric environment surrounding the palladium center; thus, an increased steric bulk visibly improved the selectivity of the bulkier polar monomer (TFP) during the copolymerization mechanism. In contrast, better activity was maintained through a sterically less hindered Pd metal center; the calculated moderate energy barriers showed that a catalyst with less steric hindrance might provide an opportunity for a wide range of prospective industrial applications.

Mechanistic study to reveal steric and electronic aspects involved in the formation of microstructures during Pd-catalyzed olefin/divinyl formal copolymerization: reactivity to catalyst choice

The advancement of metal-catalyzed copolymers is a formidable challenge for achieving distinct catalytic properties to compete with existing plastic polymers in industrial commodities. Herein, we reveal the roles of electronic and steric environments in the thermodynamic preference of microstructures in ethylene/divinyl formal (DVF) co-polymerization using a Pd catalyst under mild conditions to accommodate the respective industrial applicabilities. The insertion products of DVF result in the alteration of the steric crowding, ultimately favoring the efficient formation of cyclic units having potential applications in the manufacture of high-strength fibers. More specifically, to achieve an improved yield of the end copolymer, we tuned the catalytic activity and regioselectivity through a variety of catalysts during ethylene-DVF co-polymerization. The naphthalene-bridged (P^O)PdMe catalyst was found to be promising in terms of the least hindered (buried volume of 47.8%) environment with the thermodynamic preference of 2,1-insertion with an energy of 5.1 kcal mol^-1 among all the Pd-metal based catalysts. The highest activity with moderate energy barriers of the proposed catalyst will open new avenues for achieving a variety of potential applications, which is typically not possible using existing polymerization techniques.

Poly(ether imide) Porous Membrane Developed by a Scalable Method for High-Performance Lithium-Sulfur Batteries: Combined Theoretical and Experimental Study

Lithium-sulfur (Li-S) batteries are one of the emerging candidates for energy storage systems due to their high theoretical energy density and the abundance/nontoxicity/low cost of sulfur. Compared with conventional lithium-ion batteries, multiple new challenges have been brought into this advanced battery system, such as polysulfide shuttling in conventional polyolefin separators and undesired lithium dendrite formation of the Li metal anode. These issues severely affect the cell performance and impede their practical applications. Herein, we develop a poly(ether imide) (PEI)-based membrane with a sponge-like pore morphology as the separator for the Li-S battery by a simplified phase inversion method. This new separator can not only alleviate the new challenges in Li-S batteries but also exhibit excellent ion conductivity, better thermal stability, and higher mechanical strength compared to those of the conventional polypropylene (PP) separator. A combined experimental and theoretical study indicates that the sponge-like morphology of the PEI membrane and its good wettability toward the electrolyte can facilitate uniform ion transportation and suppress dendrite growth. Meanwhile, the PEI molecules exhibit a strong interaction with polysulfides and avoid their shuttling effectively. As a result, the PEI-based Li-S battery shows a much better performance from various aspects (capacity, rate capability, and cycling stability) than that of the PP-based Li-S battery, especially at high charge/discharge current densities and high sulfur loadings. Since the developed PEI membrane can be easily scaled up, this work may accelerate the practical applications of Li-S batteries from the point of separators.

Bridging 1D Inorganic and Organic Synthesis to Fabricate Ultrathin Bismuth-Based Nanotubes with Controllable Size as Anode Materials for Secondary Li Batteries

The growth of ultrathin 1D inorganic nanomaterials with controlled diameters remains challenging by current synthetic approaches. A polymer chain templated method is developed to synthesize ultrathin Bi₂ O₂ CO₃ nanotubes. This formation of nanotubes is a consequence of registry between the electrostatic absorption of functional groups on polymer template and the growth habit of Bi₂ O₂ CO₃ . The bulk bismuth precursor is broken into nanoparticles and anchored onto the polymer chain periodically. These nanoparticles react with the functional groups and gradually evolve into Bi₂ O₂ CO₃ nanotubes along the chain. 5.0 and 3.0 nm tubes with narrow diameter deviation are synthesized by using branched polyethyleneimine and polyvinylpyrrolidone as the templates, respectively. Such Bi₂ O₂ CO₃ nanotubes show a decent lithium-ion storage capacity of around 600 mA h g^-1 at 0.1 A g^-1 after 500 cycles, higher than other reported bismuth oxide anode materials. More interestingly, the Bi materials developed herein still show decent capacity at very low temperatures, that is, around 330 mA h g^-1 (-22 °C) and 170 mA h g^-1 (-35 °C) after 75 cycles at 0.1 A g^-1 , demonstrating their promising potential for practical application in extreme conditions.

Multivariate Linear Regression Models to Predict Monomer Poisoning Effect in Ethylene/Polar Monomer Copolymerization Catalyzed by Late Transition Metals

This study combined density functional theory (DFT) calculations and multivariate linear regression (MLR) to analyze the monomer poisoning effect in ethylene/polar monomer copolymerization catalyzed by the Brookhart-type catalysts. The calculation results showed that the poisoning effect of polar monomers with relatively electron-deficient functional groups is weaker, such as ethers, and halogens. On the contrary, polar monomers with electron-rich functional groups (carbonyl, carboxyl, and acyl groups) exert a stronger poisoning effect. In addition, three descriptors that significantly affect the poisoning effect have been proposed on the basis of the multiple linear regression model, viz., the chemical shift of the vinyl carbon atom and heteroatom of polar monomer as well as the metal-X distance in the σ-coordination structure. It is expected that these models could guide the development of efficient catalytic copolymerization system in this field.

Computational study of the copolymerization mechanism of ethylene with methyl 2-acetamidoacrylate catalyzed by phosphine-sulfonate palladium complexes

In this research, a computational study is carried out to describe the insertion of a vital monomer, methyl 2-acetamidoacrylate (MAAA), into catalyst A (A = [(POOMe,OMe)PdMe]) (POOMe,OMe = 2[2-MeOC6H4](2-SO3-5-MeC6H4)P).