Materials Chemistry Frontiers最新文献

Incorporating graphene into Ni-rich cathode materials, such as the LiNi_0.815Co_0.15Al_0.035O₂ (NCA) cathode, has been frequently reported as an effective strategy to improve the performance of lithium-ion batteries. However, the influence of the oxidation degree of graphene on the electrochemical performance of the mixed NCA/graphene cathode remains largely unexplored. In this work, the oxidation degree of graphene was tuned by varying the electrolyte concentration during the electrochemical exfoliation process, and its impact on the performance of NCA/graphene cathodes was evaluated. The results show that the exfoliated graphene (EG) synthesized using 0.3 M (NH₄)₂SO₄ (denoted as EG 0.3) possesses the lowest oxidation degree among all the samples, which leads to the highest electrical conductivity and the lowest moisture content. When incorporated into the NCA cathode, EG 0.3 produced a composite (NCA/EG 0.3) with the best rate capability and cycling stability owing to the low degree of cation mixing and the lowest charge-transfer resistance in the resulting cathode. Electrochemical measurements revealed that the NCA/EG 0.3 cathode delivers the highest specific capacity of 191.32 mA h g⁻¹ at 0.1C, 67.72% capacity retention rate at 5C compared with 0.1C, and good cycling stability (85.13% capacity retention after 100 cycles at 0.2C), which outperformed other composite cathodes. This study demonstrates that the oxidation degree of graphene can govern the cation mixing degree and charge-transfer resistance in Ni-rich cathodes, offering insights into the design of graphene-based additives and protective layers for lithium-ion battery cathodes.

Metal–organic frameworks (MOFs) and their derivatives have emerged as promising materials for membrane electrode assemblies (MEAs) in water electrolyzers. MOFs offer exceptional atomic-level tunability of metal centers and organic linkers, enabling precise control of active sites for the hydrogen evolution reactions (HER) and the oxygen evolution reactions (OER). This review presents a brief overview of state-of-the-art MOF synthesis techniques, including in situ and ex situ fabrication methods for integrating MOFs into MEAs, emphasizing scalability and interfacial engineering challenges. Strategies such as pyrolysis, defect engineering, composite formation, and multi-metal alloys are also highlighted for performance enhancements in various aspects of MEAs. This review discusses major challenges in terms of limitations of conductivity, interfacial resistance, and stability, to emphasize the importance of rational design and scalable fabrication for practical MEA production and operation. Finally, perspectives on future research directions and techno-economic considerations outline pathways to realize cost-effective, durable, and high-performance MOF-based MEAs for sustainable green hydrogen production.

In recent years, co-crystallization has emerged as an effective approach to designing room-temperature phosphorescent (RTP) materials. However, achieving long-wavelength-emissive RTP remains challenging, due to the non-radiative deactivation, which arises from the inherently small energy gap between the lowest excited triplet state (T₁) and the ground state (S₀). In this study, we constructed two orange-red RTP co-crystals based on 2,4′-bipyridine (24BD) and 1,4-diiodotetrafluorobenzene (DITF) or 1,3,5-trifluoro-2,4,6-triiodobenzene (TITF). The co-crystals exhibit distinct phosphorescence properties with main emission peaks at 570 nm, with lifetimes of 32.69 ms and 22.10 ms, respectively. Crystal structure analysis and theoretical calculations indicated that tight π–π stacking and abundant intermolecular interactions within the co-crystals are responsible for the long-wavelength RTP. Interestingly, the two co-crystals exhibit distinct acid–base stimulus-responsive properties. The phosphorescence of the 24BD-DITF crystals was quenched after acid fumigation, but recovered after subsequent alkali fumigation, owing to the cleavage and reformation of halogen bonds. In contrast, the phosphorescence of the 24BD-TITF co-crystal was quenched by acid treatment and could not be restored by alkali fumigation due to its weak halogen bond, instead showing orange fluorescence. This study introduces a new material system for achieving long-wavelength RTP in organic co-crystals, and provides a foundation for developing acid–base stimulus-responsive materials for future applications.

Hybrid reduced graphene oxide–poly(3,4-ethylenedioxythiophene) (rGO–PEDOT) nanocomposites were synthesized via green gamma-radiolysis under ambient conditions, without dopants or catalysts. Three distinct synthesis routes—including one-step simultaneous radiation induced reduction of aqueous graphene oxide (GO) and EDOT monomers and two-step approaches involving the reduction of GO in the presence of pre-formed PEDOT oligomers or polymers—were explored to assess the impact of absorbed dose and polymerization stage on the physicochemical and functional properties of the resulting materials. Extensive characterization techniques revealed that gamma-irradiation promotes effective GO reduction and controlled PEDOT polymerization, leading to significant band gap narrowing, enhanced structural ordering, and substantial increase in the carbon-to-oxygen atomic ratio (from 3.7 to 9.3) indicative of effective reduction and improved conjugation within the nanocomposites. Visual evolution confirmed kinetic-controlled composite formation, yielding hydrogel-like aggregates. Morphological analyses showed well-dispersed PEDOT on rGO sheets, contributing to improved thermal stability, enhanced optoelectronic properties and superior electrochemical performance. The composites exhibited enhanced specific capacitances up to ∼248 F g⁻¹, surpassing many reported PEDOT-based materials, attributed to the synergistic combination of rGO's conductive network and PEDOT's pseudocapacitance. This green, catalyst-free, and scalable methodology offers a promising platform for fabricating multifunctional hybrid materials with potential applications in flexible electronics, energy storage devices, and sensing technologies.

Two examples of molybdate phosphates, K₆Mo₈PO₂₉OH·H₂O and K₆Mo₅P₂O₂₃·7H₂O, were designed and synthesized using a hydrothermal method, introducing strongly distorted [MoO₆] octahedral groups. K₆Mo₈PO₂₉OH·H₂O crystallizes in the centrosymmetric space group Cmcm, where each [PO₄] combines [Mo₄O₁₅] and [Mo₄O₁₄(OH)] groups to form a unique [Mo₈PO₂₉(OH)] cluster. K₆Mo₅P₂O₂₃·7H₂O crystallizes in the non-centrosymmetric space group P2₁2₁2₁, where two [PO₄] link [Mo₅O₂₁] groups to form a closed hollow ellipsoidal [Mo₅P₂O₂₃] cluster. They possess wide experimental band gaps of 3.57 and 3.34 eV, respectively. Compared to K₃PO₄, the introduction of strongly distorted [MoO₆] octahedral groups enhances their birefringence from 0.006 to 0.127 and 0.077@1064 nm (about 21 × and 11 × K₃PO₄), with the source of the birefringence being dominated by the contribution of strongly distorted [MoO₆] octahedral groups. The relationship between its structure and optical properties is analyzed based on first-principles calculations. This work effectively enhances the birefringence properties of phosphate crystals by introducing highly distorted [MoO₆] groups, providing insights for designing and synthesizing ultraviolet optical crystal materials with superior performance.

Solid-state lithium batteries (SSLBs) hold promise for next-generation energy storage due to their high safety and energy density. However, challenges such as poor interfacial contact, high interfacial impedance, and lithium dendrite growth limit the practical application of garnet-type Li₇La₃Zr₂O₁₂ (LLZO) and its derivatives (Ta-doped Li₇La₃Zr₂O₁₂, LLZTO). This study investigates the effects of incorporating LiGaO₂ (LGO) into LLZTO to enhance grain-boundary bonding, reduce activation energy, and suppress lithium dendrite growth. LiGaO₂ powder was synthesized via a solid-state reaction and mixed with LLZTO to form composite ceramics. Structural characterization using XRD and SEM confirmed that LGO stabilizes the cubic garnet structure of LLZTO without forming impurity phases. The LLZTO-1 wt% LGO composition, sintered at 1260 °C, exhibited superior performance with a room-temperature ionic conductivity of 0.951 mS cm⁻¹ and a relative density of 96.3%. Electrochemical impedance spectroscopy shows that the interfacial resistance decreases by ∼50% (from ∼30 Ω to ∼15 Ω). The hybrid full cell retains 99.3% capacity after 200 cycles at 0.8C, showcasing practical applicability. These results highlight the effectiveness of LGO-mediated grain boundary engineering in improving the electrochemical performance of LLZTO-based solid electrolytes, paving the way for their large-scale preparation and application in SSLBs.

The transition to sustainable energy requires efficient storage technologies to manage the intermittency of renewables like solar and wind. Electrochemical devices such as supercapacitors, lithium-ion batteries, and redox flow batteries depend heavily on ion-conducting membranes for ionic transport, selectivity, and stability. Traditional membranes, including Nafion, SPEEK, and PVDF, face challenges like thermal instability and limited conductivity. To address these issues, organic framework materials have emerged as promising alternatives. This review focuses on four main classes: metal–organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic polymers (POPs), and hydrogen-bonded organic frameworks (HOFs). MOFs provide high porosity and tunability; COFs offer crystallinity and chemical stability; POPs support scalable synthesis and mechanical strength; and HOFs enable the fabrication of reversible, self-healing structures. This review explores synthesis methods, structure–property relationships, and electrochemical performance, outlining strategies to improve membrane functionality and durability in advanced energy storage systems.

Due to their excellent biocompatibility, outstanding water dispersibility, and multifunctional integration capability, carbon dots have emerged as highly promising materials for cancer phototherapy. In this study, nickel-doped carbon dots (Ni-CDs) were successfully synthesized via a one-step hydrothermal method, which enables efficient and uniform Ni incorporation within the carbon framework. Ni-CDs exhibit strong absorbance in the range of 840–1100 nm. They have a reactive oxygen species (ROS) production rate of 3.27% and a photothermal conversion efficiency of 61.33% under 1064 nm laser irradiation. The enhanced dual-mode performance can be attributed to Ni-induced nonradiative relaxation and improved electron transfer. They are the first reported nickel-doped carbon dots with synergistic therapeutic capabilities of PDT/PTT in the NIR-II region. In vitro and in vivo experiments demonstrated that Ni-CDs can effectively induce tumor cell death, with no significant toxic damage observed in normal tissues/organs. This study highlights the potential of Ni-CDs as a multifunctional nanoplatform for deep-tissue cancer treatment, providing a reference for the design of materials for the synergistic combination of photothermal and photodynamic therapy of deep tumors.

Efficient blue electroluminescent (EL) materials have been a continuing research topic for high-performance organic light-emitting diodes (OLEDs), particularly the blue emitters with the ability to utilize triplet excitons in their EL process. Herein, three donor–acceptor–donor (D–A–D) type blue fluorophores (mFS, pFS, and pPS) are systematically designed and synthesized by using diarylsulfones as acceptor cores (A) and the 1-phenyl-2-(m-tolyl)-phenanthroimidazole moiety as a π-conjugated donor (D). Different diarylsulfones (dibenzothiophene-5,5-dioxide (FS) and sulfonyldibenzene (PS)) are wisely functionalized with two donors at either meta- or para-positions. The photophysical studies and theoretical calculations verify that mFS, pFS, and pPS are blue hot exciton fluorophores with hybridized local and charge transfer (HLCT) states and decent photoluminescence quantum yields. They are effectively employed as non-doped and doped emitters in blue OLEDs with reasonable device EL performances. In particular, the doped mFS-OLED realized a deep blue emission (EL_max = 443 nm, CIE coordinates of (0.154, 0.088)) with a maximum external quantum efficiency (EQE_max) of 7.24%. Thereafter, a 2-stack white OLED is successfully fabricated using pPS as a sky-blue HLCT emitter and bis(4-phenylthieno[3,2-c]pyridinato-N,C2′)(acetylacetonate)iridium(III) (PO-01) as a complementary orange-yellow phosphorescent emitter. The white OLED achieves an EQE_max of 9.19% with CIE coordinates of (0.32, 0.31), a color-rendering index (CRI) of 79, and a correlated color temperature (CCT) of 6122 K. These results demonstrate the great potential of phenanthroimidazole–diarylsulfone-based fluorophores in developing blue organic multifunctional fluorescent materials and their OLED applications.