Monodisperse Ultrasmall Manganese-Doped Multimetallic Oxysulfide Nanoparticles as Highly Efficient Oxygen Reduction Electrocatalyst

Synthesis and symmetry of perovskite oxynitride CaW(O,N)3

Perovskite oxynitrides, in addition to being promising electrocatalysts and photoabsorbers, present an interesting case study in crystal symmetry. Full or partial ordering of the O and N anions affects global symmetry and influences material performance and functionality; however, anion ordering is challenging to detect experimentally. In this work, we synthesize a novel perovskite oxynitride CaW(O,N)3 and characterize its crystal structure using both X-ray and neutron diffraction. Through co-refinement of the diffraction patterns with a range of literature and theory-derived model structures, we demonstrate that CaW(O,N)3 adopts an orthorhombic Pnma average structure and exhibits octahedral distortion with evidence for preferred anion site occupancy. However, through comparison with a large, low-symmetry unit cell, we identify the presence of disorder that is not fully accounted for by the high-symmetry model. We compare CaW(O,N)3 with SrW(O,N)3 to demonstrate the broader presence of such disorder and identify contrasting features in the electronic structures. This work signifies an updated perspective on the inherent crystal symmetry present in perovskite oxynitrides.

Metal-Organic Framework-Derived Ni-S/C Catalysts for Selective Alkyne Hydrogenation

A carbon matrix-supported Ni catalyst with surface/subsurface S species is prepared using a sacrificial metal-organic framework synthesis strategy. The resulting highly dispersed Ni-S/C catalyst contains surface discontinuous and electron-deficient Niδ+ sites modified by p-block S elements. This catalyst proved to be extremely active and selective for alkyne hydrogenation. Specifically, high intrinsic activity (TOF = 0.0351 s-1) and superior selectivity (>90%) at complete conversion were achieved, whereas an analogous S-free sample prepared by the same synthetic route performed poorly. That is, the incorporation of S in Ni particles and the carbon matrix exerts a remarkable positive effect on catalytic behavior for alkyne hydrogenation, breaking the activity-selectivity trade-off. Through comprehensive experimental studies, enhanced performance of Ni-S/C was ascribed to the presence of discontinuous Ni ensembles, which promote desorption of weakly π-bonded ethylene and an optimized electronic structure modified via obvious p-d orbital hybridization.

Ionothermal Access to Defined Oligomers of Supertetrahedral Selenido Germanate Clusters

Supertetrahedral chalcogenido (semi)metalate clusters have been in the focus of inorganic and materials chemistry for many years owing to a variety of outstanding physical and chemical properties. However, a critical drawback in the canon of studying corresponding compounds has been the lack of control in assembling the supertetrahedral units, which have been known as either highly charged monomeric cluster anions or lower charged, yet extended anionic substructures of linked clusters. The latter is the reason for the predominance of applications of such materials in heterogeneous environment, or their solubilization by organic shielding, which in turn was unfavorable regarding the optical properties. Recently, we reported a partial alkylation of such clusters, which allowed for a significantly enhanced solubility at a marginal impact on the optical gap. Herein we showcase the formation of finite cluster oligomers of supertetrahedral architectures by ionothermal syntheses. We were successful in generating the unprecedented dimers and tetramers of the [Ge₄Se₁₀]^4- anion in salts with imidazolium-based ionic liquid counterions. The oligomers exhibit lower average negative charges and thus reduced electrostatic interactions between anionic clusters and cationic counterions. As a consequence, the salts readily dissolve in common solvents like DMF. Besides, the tetrameric [Ge₁₆Se₃₆]^8- anion represents the largest discrete chalcogenide cluster of a group 14 element. We prove that undestroyed cluster oligomers can be transferred into solution by means of electrospray ionization (ESI) mass spectrometry and provide a full set of characteristics of the compounds including crystal structures and optical properties.

Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

This review introduces recent advances of various anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, (oxy)hydroxides, and borides) for efficient water electrolysis applications in detail. The challenges and future perspectives are proposed and analyzed for the anion-mixed water dissociation catalysts, including polyanion-mixed and metal-free catalyst, progressive synthesis strategies, advanced in situ characterizations, and atomic level structure-activity relationship. Hydrogen with high energy density and zero carbon emission is widely acknowledged as the most promising candidate toward world's carbon neutrality and future sustainable eco-society. Water-splitting is a constructive technology for unpolluted and high-purity H₂ production, and a series of non-precious electrocatalysts have been developed over the past decade. To further improve the catalytic activities, metal doping is always adopted to modulate the 3d-electronic configuration and electron-donating/accepting (e-DA) properties, while for anion doping, the electronegativity variations among different non-metal elements would also bring some potential in the modulations of e-DA and metal valence for tuning the performances. In this review, we summarize the recent developments of the many different anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, oxyhydroxides, and borides/borates) for efficient water electrolysis applications. First, we have introduced the general information of water-splitting and the description of anion-mixed electrocatalysts and highlighted their complementary functions of mixed anions. Furthermore, some latest advances of anion-mixed compounds are also categorized for hydrogen and oxygen evolution electrocatalysis. The rationales behind their enhanced electrochemical performances are discussed. Last but not least, the challenges and future perspectives are briefly proposed for the anion-mixed water dissociation catalysts.

Mixed Solvothermal Synthesis of Tn Cluster-Based Indium and Gallium Sulfides Using Versatile Ammonia or Amine Structure-Directing Agents

Metal chalcogenide supertetrahedral Tn clusters are of current interest for their unique compositions and structures, which rely highly on the structure-directing agents. Herein, we report four novel Tn cluster-based indium and gallium sulfides, namely, [NH(CH₃)₃]₄In₄S₁₀H₄ (1), (NH₃)₄Ga₄S₆ (2), [NH₃CH₂CH₃]₅(NH₂CH₂CH₃)₂Ga₁₁S₁₉ (3), and [NH₃CH₂CH₂OH]₆Ga₁₀S₁₈·2NH₂CH₂CH₂OH (4). All four compounds were solvothermally synthesized in mixed amine-ethanol solutions or deep eutectic solvent (DES), where ammonia/amine molecules play significant structure-directing roles in the speciation and crystal growth. (1) Being protonated, the trimethylamine and ethanolamine molecules surround the T2-[In₄S₁₀H₄]^4- clusters (for 1) and [Ga₁₀S₁₈]_n^6n- open framework (for 4), respectively, compensating for the negative charge of the inorganic moieties. (2) With the lone pair of electrons, the ammonia molecules in 2 coordinate directly to corner Ga³⁺ ions of the {Ga₄S₆} cage to give a neutral T2-(NH₃)₄Ga₄S₆ cluster. (3) For compound 3, part of the ethylamine molecules act as terminating ligands for the T1 and T3 units in the [Ga₁₁S₁₉(NH₂CH₂CH₃)₂]_n^5n- layer, while the rest act as interlamellar countercations upon protonation. Theoretical studies reveal the contributions of N, C, and H to the density of states (DOS) for 2 and 3 because of their hybrid structures that combine the ammonia/amine ligands with sulfide moieties together.

Metal Chalcogenide Supertetrahedral Clusters: Synthetic Control over Assembly, Dispersibility, and Their Functional Applications

ConspectusMetal chalcogenide supertetrahedral clusters (MCSCs) bear the closest structural resemblance to II-VI or I-III-VI semiconductor nanocrystals and can be considered as well-defined ultrasmall "quantum dots" (QDs). Compared to traditional colloidal QDs that are typically associated with size dispersity, irregular surface atomic structures, poorly defined core-ligand interfaces, and random defect/dopant sites, the nano- or subnano-sized MCSCs feature precise structural properties such as atomically uniform size, precise structure, and ordered dopant distribution, all of which offer ample opportunities for a broad and in-depth understanding of the correlation between the precise local structure and site- or size-dependent properties, which are critical to the exploitation of their functional applications. Our previous Account in 2005 provided a narrative on the efforts to expand the structural diversity of open-framework materials using different-sized and compositionally tunable clusters as building blocks with a primary objective of integrating the semiconducting properties with porosity in zeolite-type solids. Over the past 15 years, significant progress has been made, particularly in the synthetic control of discrete clusters, allowing the establishment of the composition-structure-property correlation of the MCSCs to guide the optimization of their properties for various applications. In the present Account, the recent progress in MCSC-based chemistry is reviewed from three aspects: (1) controllable synthesis of new members and types of MCSC models and the development of organic-ligand-directed hybrid assembly modes for MCSC-based open frameworks; (2) new synthetic strategies for the discretization of MCSCs in crystal lattice and their dispersibility in solvents, affording practical applications of pure inorganic MCSCs as nanomaterials; and (3) functionality of MCSC-based materials including photochemical and electrochemical properties triggered by precise dopant/defect sites, open-framework-related functional expansion via host-guest chemistry, and dispersed cluster-based composite materials with synergy from functional multimetallic components. All these advances show that MCSCs with well-defined structures and atomically precise dopant/defect sites are powerful model systems for establishing the precise structure-composition-property correlation and understanding the photophysical dynamic behaviors, both of which are difficult or impossible to achieve in the traditional QD system. Perspectives on their potential applications are presented in terms of the amorphous assemblies of monodispersed MCSCs, MCSC-based two-dimensional layered materials, and optical/electronic devices.

Direct observation of charge transfer between molecular heterojunctions based on inorganic semiconductor clusters

A deep understanding of the dynamics of photogenerated charge carriers is extremely important for promoting their germination in semiconductors to enhance the efficiency of solar energy conversion. In contrast to that of organic molecular heterojunctions (which are widely employed in organic solar cells), the charge transfer dynamics of purely inorganic molecular heterojunctions remains unexplored. Herein, we reveal the dynamics of charge transfer between inorganic semiconductor molecular heteroclusters by selecting a group of open-framework metal chalcogenides as unique structure models constructed from supertetrahedral T3-InS ([In₁₀S₂₀]) and T4-MInS ([M₄In₁₆S₃₅], M = Mn or Fe) clusters. The staggered band gap alignment in T3-T4-MInS molecular heterojunctions enables the photogenerated charge carriers to be directionally transferred from T3-InS clusters to adjacent T4-MInS clusters upon irradiation or application of an external electric field. The simultaneous independence of and interactions between such two heteroclusters are investigated by theoretical calculations, steady- and transient-state absorption/photoluminescence spectroscopy, and surface photovoltage analysis. Moreover, the dynamics of cluster-to-cluster-to-dopant photogenerated charge transfer is deliberately elucidated. Thus, this work demonstrates the direct observation of charge transfer between molecular heterojunctions based on purely inorganic semiconductor clusters and is expected to promote the development of cluster-based semiconductors for solar cells.

Charge transfer between inter-clusters is directly observed in inorganic molecular heterojunctions.

Synthesizing Crystalline Chalcogenidoarsenates in Thiol-Amine Solvent Mixtures

Thiol-amine solvent mixtures have been widely applied in the solution processing of binary chalcogenide thin films due to their excellent ability to dissolve various bulk binary chalcogenides. However, application of this solvent system in preparing new crystalline chalcogenidometalates has not been explored. In this work, by using a thiol-amine solvent mixture of n-butylamine (BA) and 1,2-ethanedithiol (EDT) as the reaction medium and protonated piperazine (pip) cation as the template, we synthesized a series of new chalcogenidoarsenates with structures ranging from discrete clusters to two-dimensional layers, namely, [pipH₂][pipH][AsS₄] (1), [pipH₂][pipH][As(Se_0.4S_0.6)₄] (2), [pipH₂]₂[pipH]₂[In₂As^III₂As^V₂S_13.3(S₂)_0.7] (3), [pipH₂]₂[pipH]₂[In₂As^III₂As^V₂S_10.2Se_3.1(Se₂)_0.7] (4), [pipH₂]_0.5[AsS(S₂)] (5), [pipH₂]_0.5[AsS₂] (6), [pipH]₂[AgAsS₄] (7), [pipH₂]_1.5[GaAs^IIIAs^VS₇] (8), and Cs₂[pipH]₂[InAs₆S₁₂]Cl (9). Particularly, compounds 3, 4, and 8 contain mixed-valent As^III and As^V ions in their discrete clusters and one-dimensional chain. In addition, compound 5 could thermodynamically transform to compound 6 with increasing reaction temperature, which may be attributed to the thermodynamically unstable S-S species in the chains of 5. The BA-EDT solvent mixture was crucial to the synthesis of these compounds, since no title crystals can be prepared by replacing the BA-EDT solvent mixture with other conventional solvents or removing one component of the BA-EDT solvent mixture from the reaction system. Our research demonstrates that thiol-amine solvent systems could be promising reaction media for growing novel crystalline chalcogenidometalates.

Effect of Thermally Induced Oxygen Vacancy of α-MnO2 Nanorods toward Oxygen Reduction Reaction

MnO₂ has been explored for various applications in environmental and energy aspects. However, the thermal sensitivity of the MnO₂ crystal structure never been studied. As a potential cathode material for fuel cell, α-MnO₂ has a higher specific activity than Pt/C based on per metals cost. In this work, the physical and electrochemical properties of α-MnO₂ nanorods were explored for the first time under thermal treatment with different temperatures (300, 400, and 500 °C). Under thermal treatment, oxygen vacancies were induced. The high-angle annular dark-field (HAADF) images and electron energy loss spectroscopy (EELS) have been taken to explore oxygen vacancies of α-MnO₂ materials. From EELS and X-ray photoelectron spectroscopy (XPS) analysis, the oxygen vacancies on the α-MnO₂ nanorods were strengthened with the temperature increasing. The sample with 400 °C treatment exhibited the best performance toward ORR, excellent methanol tolerance and higher stability compared to commercial Pt/C in alkaline media due to its combination of preferable growth on (211) plane and moderate oxygen vacancies as well as coexistence of Mn (IV)/ Mn (III) species. It was also observed the α-MnO₂ nanorods tended to become longer and thinner with increasing temperature. This work suggests that the α-MnO₂ nanorods are thermal sensitive materials and their performance for ORR can be boosted under certain temperatures.

Three-Dimensional Superlattices Based on Unusual Chalcogenide Supertetrahedral In-Sn-S Nanoclusters

Reported here are two novel metal chalcogenide superlattices built from unusual supertetrahedral TO2-InSnS clusters. With regard to only one previously reported case of a TO2-InS-based 2D-layered structure, such a combination of In-Sn-S components is thought to be reasonable for leading to the first observation of 3D superlattices based on TO2-InSnS clusters. Besides, these title semiconducting materials also display good performance on the electrocatalytic oxygen reduction reaction.

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle

A new cluster-based chalcogenide zeolite analogue with a large inter-cluster bridging angle.