Chemistry of Materials最新文献

Hard carbons are the leading anode material in Na-ion batteries due to their considerable ability to store Na, and the ease with which they can be produced from inexpensive precursors such as cellulose through pyrolysis in inert atmospheres. Here, we report a rapid one-step conversion of cellulose to hard carbons in under 15 min in a modified domestic microwave oven. This is in contrast to more conventional furnace-based pyrolysis which can take several hours. From optical pyrometry, we find that under different microwave power conditions, the hard carbons can be tunably formed at temperatures between 900 to 1250 °C under the conditions employed. The hard carbons produced here have been characterized by Raman spectroscopy, wide and small-angle X-ray diffraction, porosimetry, X-ray photoelectron spectroscopy, and X-ray pair distribution function analysis. As a function of increasing microwave power, the carbons are found to exhibit comparable local structure but enhanced crystallinity and evidence of an increased proportion of closed pores. The formation of closed pores appears to directly contribute to significant gains in Na storage capacity throughout the plateau region during electrochemical cycling. These results demonstrate a convenient and scalable strategy for rapidly producing hard carbons with tunable porosity.

We present a systematic first-principles screening of metal fluorides reported in polar crystallographic point groups to identify new candidates for ferroelectric materials. From an initial set of 57 distinct polar structure types collected from crystallographic databases, we classified each entry by crystallographic group-subgroup analysis, hybrid density functional theory (DFT) calculations, and machine-learning-based similarity search into one of the three categories: potentially ferroelectric structures, pyroelectric but nonferroelectric compounds, and structures likely based on wrong polar structure models. Our analysis yields 20 potentially ferroelectric compounds, including 14 new structure types that are further ranked by a one-class support vector machine (SVM) similarity analysis. Promising ferroelectric candidates include KNaSnF₆, NaSrAlF₆, KYF₄ and the possibly multiferroic RbCrF₅. With tetragonal antiprismatic coordinated Hf atoms the compound Pb₂HfF₈ introduces a new structural motive for ferroelectricity, whereas Mn₃F₈ is a new candidate for a charge-ordered ferroelectric. Together, these compounds expand the structural chemistry of fluoride ferroelectrics beyond the classical BaZnF₄ type. We further report 14 pyroelectric candidates that lack centrosymmetric reference phases and are therefore structurally precluded from ferroelectric switching. In addition, we identified 23 structure types based on possibly wrong polar models. For these compounds, DFT structure optimizations systematically relax into centrosymmetric crystal structures, in line with earlier corrections reported in the literature. Among them, Sr₄Zn₃F₁₄, NaMn₃F₁₀, RbTlF₄ and δ-Na₂UF₆ remain uncorrected in crystallographic databases and require experimental reinvestigation. Our findings highlight that about 40% of the reported polar fluorides are likely misassigned, underlining the need for critical crystal structure validation prior to high-throughput searches. At the same time, the newly identified ferroelectric candidates offer promising directions for expanding the family of fluoride-based functional materials.

Developing electrocatalysts for CO₂ reduction is essential for the effective use of renewable energy. Materials containing molecules such as coordination polymers have strong potential to exhibit high activity and selectivity. However, a critical shortcoming is that they often decompose into metals or metal oxides during reactions, thereby preventing the manifestation of functions unique to molecular structures. In this study, we compare a series of Pb–S-based coordination polymers, [Pb(x-SPhOMe)₂]_n (HSPhOMe = methoxybenzenethiol, x = ortho (KGF-32), meta (KGF-33), and para (KGF-34)), as model electrocatalysts to investigate the design guidelines. They have different crystal structures in terms of dimensionality and coordination environment. Among them, KGF-32 shows the highest Faradaic efficiency for formate production: 96.6 ± 2.9% at −1.0 V vs RHE with a partial current density of −9.76 ± 2.1 mA cm^–2. By contrast, KGF-33 and -34 show lower Faradaic efficiencies for formate production, along with more pronounced decomposition to PbCO₃. We use scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to confirm that KGF-32 retains much of its crystal structure during operation, whereas KGF-33 and -34 decompose extensively. In addition, density functional theory calculations reveal that the energy barrier for formate production on KGF-32 is lower than that on PbCO₃, which explains its superior catalytic activity. Our work demonstrates the inherent advantages of coordination-polymer-based electrocatalysts and provides valuable guidelines for designing more efficient and stable systems for CO₂ reduction.

The rapid advancement of flexible electronic technologies, including wearable electronics, implantable medical devices, and smart textiles, has spurred a growing interest in developing biocompatible, high-performance, and flexible energy-storage systems. Among these, fiber-shaped supercapacitors have emerged as promising candidates for next-generation flexible power sources due to their high power density, long cycle life, and excellent flexibility. In this regard, nanomaterial-based composites have been developed to further enhance their performance and practical applicability. This review systematically summarizes recent research progress in fibrous supercapacitors, with a special emphasis on design strategies and performance optimization related to established fabrication methods (such as wet spinning and coating), typical structural configurations (parallel, twisted, and coaxial designs), and key electrode materials (including metal wires, carbon-based substances, graphene, and MXene). Furthermore, this article highlights cutting-edge applications of fibrous supercapacitors in self-powered systems, wearable electronics, and biomedical devices, and discusses the prevailing challenges and future directions for their large-scale fabrication, system integration, and practical deployment.