Materials Chemistry Frontiers最新文献

Developing thermally activated delayed fluorescence (TADF) emitters showing high horizontal transition dipole orientation and molecular rigidity is crucial for enhancing the color purity and performance of deep-blue organic light-emitting diodes (OLEDs). Here, we report two linearly expanded TADF emitters, O-tsAC-BAsBP (1) and S-tsAC-BAsBP (2), based on a tri-spiral acridine donor and a spiro-fluorenyl B-heterotriangulene acceptor. These emitters exhibit deep-blue emissions, with peaks centered at 458–467 nm for 1 and 462–469 nm for 2, respectively, in the host films, with high photoluminescence quantum yields, small singlet–triplet energy splitting (ΔE_ST < 0.05 eV), and short delayed fluorescence lifetimes (τ_d < 2 μs). Theoretical studies demonstrate that effective spin–orbit coupling between the charge transfer singlet (¹CT) and acceptor-centered local triplet (³LE) excited states accelerates the reverse intersystem crossing (RISC) process, resulting in a high RISC rate constant of ∼10⁶ s⁻¹. Notably, both emitters exhibit very high horizontal dipole orientation ratios (Θ_‖) of ∼93% in their doped host films. Owing to the outstanding TADF characteristics and high Θ_‖ values, TADF-OLEDs incorporating emitters 1 and 2 achieve high maximum external quantum efficiencies of 27.4% and 31.5%, respectively, in the deep-blue region.

In this work, calixpyridinium was found to be a good building block for constructing an unusual artificial dissipative system with a proton donor by using an alkali as the fuel. Inspired by this, the structural evolution from disordered to fibrous assembly based on a calixpyridinium–indigo carmine system via a dual visual dissipative pathway with an alkali as the fuel was achieved. This was further applied in mimicking an alkaline biological molecule-driven dissipative process in real samples.

Covalent organic frameworks (COFs) have attracted much attention recently as potential photocatalysts for the hydrogen evolution reaction (HER). Linkage isomerism in COFs usually has an important effect on their physicochemical properties. However, the effect of linkage isomerism on the photocatalytic HER performance has been rarely studied. Herein, a pair of COFs with isomeric imine bonds was synthesized, and thus a pair of isomeric amide materials was obtained by oxidation. The photocatalytic HER experiments demonstrated that the photocatalytic HER rates of the isomeric imine COFs were 110.6 and 4.8 μmol h⁻¹, respectively, while those of the amide materials were 2.1 μmol h⁻¹ and negligible, respectively. This indicates that linkage isomerism does have a significant impact on the photocatalytic HER performance. The main reason for this effect is that linkage isomerism leads to prominent differences in light absorption, charge carrier separation and transport, and interfacial reactivity of the two pairs of isomeric materials. Evidently, this work provides a new strategy for designing high-performance COF catalysts.

The development of high-performance proton-conducting materials with outstanding chemical/physical stability is critical for the fabrication of proton-exchange membrane fuel cells (PEMFCs), and remains a significant challenge. Herein, a one-pot in situ oxidation strategy is developed to construct a pyrazine-linked conjugated microporous polymer (HD-CMP) at the gram scale from hexahydroxy triphenylene and benzenetetramine tetrahydrochloride in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in the autoclave. The obtained HD-CMP not only exhibits extended π-conjugated structures and exceptional chemical stability under harsh conditions, but also nitrogen sites on the pyrazine functional groups could serve as binding sites for anchoring H₃PO₄ as proton carriers. Furthermore, contact angle measurements and water adsorption isotherms indicate the high water uptake capacity and hydrophilic properties of H₃PO₄@HD-CMP. Attributed to these features, the resulting H₃PO₄@HD-CMP exhibits a high proton conductivity of 1.05 × 10⁻¹ S cm⁻¹ at 80 °C under 100% RH, which can be comparable to those of most materials currently reported.

Electrochemical reduction of CO₂ into fuel/high-value chemicals using electricity generated from renewable energy is one of the most promising ways to achieve carbon neutrality. Recently, metal–organic frameworks (MOFs)-derived materials, originating from the MOF architecture, show competitive performance as electrocatalysts in CO₂ reduction. This review systematically summarizes several synthesis strategies to fabricate diverse and functional MOF-derived materials including pyrolysis, precursor regulation, post-modification and other synthesis. Additionally, the application of MOF-derived materials in the ECO₂RR is classified in detail according to the reduction products. Eventually, some challenges and prospects of the synthesis of MOF-derived electrocatalysts and their application in ECO₂RR are presented.

Polymer-based electrolytes have high interface compatibility, good safety, and remarkable processability and are ideal for solid-state lithium batteries. However, the electrochemical performance of solid-state lithium batteries deteriorates severely at high or low temperatures, resulting in dramatic energy and power loss, cycling lifetime degradation, and safety issues. Herein, the latest advances of polymer-based electrolytes for solid-state lithium batteries are reviewed for wide temperature applications. The limitations for battery developments under high or low temperatures are systematically analyzed, with special focus on the ion transport kinetics and the interfacial stability between electrodes and the electrolyte. Applications of polymer-based electrolytes in solid-state lithium batteries that can work over a wide temperature range are summarized. Moreover, perspectives of polymer-based electrolytes for solid-state lithium batteries are also outlined.

Hydrogen energy has been regarded as a potential energy source for the future economy. In order to realize the clean and efficient utilization of hydrogen energy, sustainable energy conversion technology needs to be developed. Overall water splitting (OWS) and zinc–air batteries (ZAB), which involve the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), are two typical energy storage and conversion techniques. However, they are limited by slow reaction kinetics and high thermodynamic overpotential, and thus require highly active, stable and low-cost catalysts to overcome this energy barrier. In recent years, carbon-based electrocatalysts have attracted increasingly more attention due to their various advantages, among which fullerene is regarded as a promising material due to its definite molecular structure and excellent electron acceptability. In this study, the synthesis methods of fullerene-based electrocatalysts commonly used in recent years are first summarized. Then, their applications are reviewed from the aspects of HER, OER, ORR, OWS, and ZAB, as well as carbon dioxide reduction reaction (CO₂RR) and methanol oxidation reaction (MOR). Finally, a brief outlook and prospective for future investigations on the design and construction of novel fullerene-based electrocatalysts and related mechanism analysis is also provided.

Water electrolysis is a possible method for producing ultrapure hydrogen (H₂). However, the typical water electrolysis process has significant overpotential, mostly because of the slow kinetics in the oxygen evolution reaction (OER). The OER that produces reactive oxygen species weakens the proton exchange membrane in the water electrolyzer. Besides, oxygen can interact with cathodic H₂ to create explosive gaseous mixtures. These issues can be solved using the hybrid water electrolysis (HWE) method, replacing the OER with an alternative oxidation reaction. The oxidizing chemical agent helps in electrochemical hydrogen production at extremely low voltage while oxidizing the substance to value-added products in the HWE process. Electrocatalysts are used to power the chemical species-assisted hydrogen generation in the HWE process. Quaternary metal sulfide, a highly electrochemically active material, has attracted attention as a promising platform for effective application in various redox reactions. In this work, we reported quaternary copper–iron–tin sulfide with the chemical formula Cu₂FeSnS₄ (CFTS) in the form of nanosheets and evaluated the HWE with the ammonia oxidation reaction at the anode. The CFTS nanosheets were synthesized by a facile one-step solvothermal method using carbon cloth (CC) as the substrate. To evaluate the effect of solvents used in the synthesis process on the morphology and electrochemical performance of the material, deionized water (DI), ethanol (EtOH), and ethylene glycol (EG) were applied, and their effects were studied thoroughly. A feasible formation mechanism has been presented in which the viscosity and dielectric constants of the solvents play key roles in determining the morphology of CFTS nanosheets. The CFTS nanosheets synthesized in EG showed a porous and rougher surface than those produced using other solvents. As expected, the EG-mediated CFTS exhibited remarkable H₂ production with ammonia oxidation at the anode due to better electron and electrolyte ion transmission. Our results describe the effect of solvents used for solvothermal reactions and that the CFTS material can be deliberated as a potential alternative for divergent energy conversion device applications.

Discrete molecular cages, as artificial mimics of protein cavities, are central to various applications. Anionocages have emerged in the past two decades as a new type of molecular cage, utilizing anion coordination (hydrogen-bonding in nature) as the driving force of self-assembly rather than the widely utilized metal coordination. In this Chemistry Frontiers paper, we will introduce the historical background of anionocages and summarize their critical features, highlighting the high sensitivity of the assemblies in response to external stimuli. Finally, advances of anionocages are introduced in terms of the coordination nodes and critical features of organophosphate-directed anionocages.

Acidification of traditional commercial electrolytes arising from LiPF₆ degradation severely affects the long-term durability of lithium-ion batteries. In particular, the moisture introduced during battery fabrication and operation leads to hydrogen fluoride generation and triggers a series of parasitic reactions, resulting in the decomposition of a solid electrolyte interphase and the structure destruction of electrodes. Acid-scavenging separators are a promising option to solve the above problems without changing the existing electrode and electrolyte preparation industries, especially for widely applied lithium-ion batteries using LiPF₆-containing electrolytes. So far, various advanced acid-scavenging separators have been developed, but there is no comprehensive review that systematically elucidates the importance of acid-scavenging separators. In this review, the mechanism of LiPF₆ degradation on the acidification of traditional commercial electrolytes is firstly discussed from the perspective of internal battery components. Subsequently, the acid removal mechanism, electrochemical characteristics, and long-cycle performance of the acid-removing separators are summarized. Further developments and challenges of the acid-scavenging separators are outlined. Finally, future applications and research directions of the acid-scavenging separators are proposed.