Ling Lin

This study explores high-entropy sulfides (HESs) as potential electrocatalysts for the hydrogen evolution reaction (HER). Novel Pa-3 and Pnma structured HESs containing Fe, Mn, Ni, Co and Mo, were synthesized via a facile mechanochemical method. Structural and chemical properties were extensively characterized using x-ray diffraction, transmission electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The electrocatalytic performance of four as-prepared HESs in alkaline electrolyte for HER reveals the remarkable outperformance compared to medium-entropy and conventional sulfides. Particularly, (Fe_0.2Mn_0.2Ni_0.2Co_0.2Mo_0.2)S₂ demonstrated outstanding activities, with minimal overpotentials (187 mV at 10 mA cm^–2) and outstanding durability under harsh alkaline conditions (a mere polarization increase ΔE = 17 mV after 14 h via chronopotentiometry). The remarkable catalytic activities can be attributed to synergistic effects resulting from the cocktail effects within the high-entropy disulfide. The introduction of Mo contributes to the formation of a layered structure, which leads to an increased surface area and thus to a superior HER performance compared to other HES and conventional sulfides. This work demonstrates the promising potential of HES and underscores that further development for catalytic applications paves the way for innovative routes to new and more efficient active materials for HER catalysis.

Elektron‐Phonon‐Wechselwirkungen, die in kondensierter Materie von entscheidender Bedeutung sind, werden in metallorganischen Gerüstverbindungen (MOFs) selten beobachtet. In Lanthanoid‐ oder Actinoid‐basierten Verbindungen gelingt der Nachweis dieser Wechselwirkungen typischerweise über die Analyse der Lumineszenz. Frühere Studien zu Ln‐ und Ac‐basierten MOFs bei hohen Temperaturen ergaben zusätzliche Lumineszenzsignale, die jedoch zu schwach für eine gründliche Analyse waren. Im Rahmen unserer Untersuchungen haben wir mithilfe eines Schicht‐für‐Schicht‐Verfahrens eine hochgeordnete, kristalline uranbasierte MOF‐Dünnschicht (KIT‐U‐1) hergestellt. Unter UV‐Licht zeigte diese Schicht zwei ausgeprägte „heiße Banden“, die auf eine starke Elektron‐Phonon‐Wechselwirkung hinweisen. Während bei 77 K keine Emissionsbanden sichtbar waren, erschien bei 300 K eine Emissionsbande mit der halben Intensität der Hauptbande. Überraschenderweise tauchte oberhalb von 320 K eine zweite, sogenannte heiße Bande auf, die von früheren Ergebnissen aus Seltenerd‐Verbindungen abweicht. Wir haben eine detaillierte ab initio‐Analyse mithilfe der zeitabhängigen Dichtefunktionaltheorie durchgeführt, um dieses ungewöhnliche Verhalten zu verstehen und die für die starke Elektron‐Phonon‐Kopplung verantwortliche Gitterschwingung zu identifizieren. Die heißen Emissionsbanden der KIT‐U‐1‐Schicht wurden dann dazu genutzt, ein hochempfindliches optisches Einkomponenten‐Thermometer zu entwickeln. Diese Ergebnisse belegen das Potenzial hochwertiger MOF‐Dünnschichten bei der Nutzung der einzigartigen Lumineszenz von Lanthanoiden und Actinoiden für neuartige Anwendungen.

Electron‐phonon interactions, crucial in condensed matter, are rarely seen in Metal–Organic Frameworks (MOFs). Detecting these interactions typically involves analyzing luminescence in lanthanide‐ or actinide‐based compounds. Prior studies on Ln‐ and Ac‐based MOFs at high temperatures revealed additional peaks, but these were too faint for thorough analysis. In our research, we fabricated a high‐quality, crystalline uranium‐based MOF (KIT‐U‐1) thin film using a layer‐by‐layer method. Under UV light, this film showed two distinct “hot bands,” indicating a strong electron‐phonon interaction. At 77 K, these bands were absent, but at 300 K, a new emission band appeared with half the intensity of the main luminescence. Surprisingly, a second hot band emerged above 320 K, deviating from previous findings in rare‐earth compounds. We conducted a detailed ab‐initio analysis employing time‐dependent density functional theory to understand this unusual behaviour and to identify the lattice vibration responsible for the strong electron‐phonon coupling. The KIT‐U‐1 film's hot‐band emission was then utilized to create a highly sensitive, single‐compound optical thermometer. This underscores the potential of high‐quality MOF thin films in exploiting the unique luminescence of lanthanides and actinides for advanced applications.

With respect to efficient use of diminishing or harder to reach energy resources, the catalysis of processes that will otherwise require high overpotentials is a very important application in today's world. As a newly developed class of materials, high‐entropy sulfides (HESs) are promising electrocatalysts for a variety of different reactions. In this report, HESs containing five or six transition metals are synthesized in a one‐step mechanochemical process. Seven HESs of Pnma (M:S≈1:1) and three Pa‐3 (M:S = 1:2) structures are investigated as electrocatalysts for the oxygen evolution reaction (OER). The performances and properties of the HESs with different compositions and structures are compared with each other and with commercial IrO₂ as reference material, in terms of OER overpotential, Tafel slope, electrochemically active surface area, ionic conductivity, and durability. The structural and chemical properties of these HESs are determined by X‐ray diffraction, transmission electron microscopy, scanning electron microscopy, X‐ray photoelectron spectroscopy, and energy‐dispersive X‐ray spectroscopy. Most of the HESs show excellent and promising performance as OER electrocatalysts under alkaline conditions, and outperform the reference OER catalyst IrO₂.

Oxygen vacancy-rich high-entropy (Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2)₃O₄ oxide nanofibres with granular structure are good candidates for the preparation of electrocatalytic inks.

High‐entropy sulfides (HESs) containing 5 equiatomic transition metals (M), with different M:S ratios, are prepared by a facile one‐step mechanochemical approach. Two new types of single‐phase HESs with pyrite (Pa‐3) and orthorhombic (Pnma) structures are obtained and demonstrate a homogeneously mixed solid solution. The straightforward synthesis method can easily tune the desired metal to sulfur ratio for HESs with different stoichiometries, by utilizing the respective metal sulfides, even pure metals, and sulfur as precursor chemicals. The structural details and solid solution nature of HESs are studied by X‐ray diffraction, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, electron energy loss spectroscopy, X‐ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, and Mössbauer spectroscopy. Since transition metal sulfides are a very versatile material class, here the application of HESs is presented as electrode materials for reversible electrochemical energy storage, in which the HESs show high specific capacities and excellent rate capabilities in secondary Li‐ion batteries.

A facile mechanochemical reaction at ambient temperature was successfully applied to synthesize novel single-phase rock-salt-structured high-entropy oxides, containing five, six and seven metal elements in equiatomic amounts. This synthesis approach overcomes the limitations of the commonly known synthesis procedures, which would result in multiple-phase compounds. Redox-sensitive elements, such as Fe²⁺ and Mn²⁺, can now be considered. The corresponding single-phase Li-containing high-entropy oxyfluorides were obtained by introducing LiF into the lattice using the same strategy. All materials show single-phase rock-salt structures with lattice parameters depending on the incorporated ion sizes. Solid solution states result in high configurational entropies, and all elements appear homogenously distributed over the whole cationic and anionic sublattice. The straightforward synthesis technique, combined with utilized simple binary oxide precursors, paves the way for a multitude of novel high-entropy oxide and oxyfluoride compounds. The compounds were studied by means of X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Mössbauer spectroscopy.

Porous metal–organic frameworks (MOFs) with an extensive range of pore sizes have great potential for efficient separation of small organic molecules. Herein, we report a new stable porous metal–organic framework {Cu₃L₂(4,4′-BPD)[NH(CH₃)₂]·7DMA·12H₂O}_n (YCZ-1), which was fabricated from a Cu-paddlewheel metal node and a new linker, namely 3,6-bis(4-benzoic acid)-N-(4-benzoic acid) carbazole (H₃L). YCZ-1 possesses a doubly interpenetrated 3,5,6-connected three-dimensional (3D) framework with a Schläfli symbol of {5¹²·8³}·{5²·8}₄·{5⁶·8⁴}₂, which is a new topology. The crystalline size of YCZ-1 could be controlled by adding different doses of dimethylamine, which would also be generated from DMA dissociated during the solvothermal reaction. Meanwhile, with excellent structural stability and outstanding surface area, the crystalline material YCZ-1 could be utilized as a stationary phase for high performance liquid chromatography (HPLC) separations during the separation of small organic molecules.

A novel tetranuclear Ag(I) complex, [Ag₄(μ-DMPTP)₂(POP)₃][BF₄]₂ (Ag₄N₂P₃), has been designed to achieve highly efficient thermally activated delayed fluorescence (TADF). Photophysical investigations show that the compound exhibits highly efficient TADF (Φ = 76%) and has a very short ambient-temperature TADF decay time of only 0.65 μs, corresponding to a radiative decay rate of k = Φ/τ = 1.2 × 10⁶ s⁻¹, a value belonging to the fast radiative rates in TADF materials.