A hierarchical CoSx/Ni(OH)2 heterostructure as a bifunctional electrocatalyst for urea-assisted energy-efficient hydrogen production.

We report hierarchical CoSx/Ni(OH)2/NF heterostructure nanorod arrays, which manifest superior bifunctional catalytic activities for the HER and UOR due to amorphous Ni(OH)2, synergistic effect of multiple components and self-supported structure. The CoSx/Ni(OH)2/NF-based urea electrolyzer requires a low cell voltage of 1.485 V to deliver 10 mA cm-2, which is obviously lower than that needed in water electrolysis.

New crystalline 1D/2D/3D indium selenides directed by piperidine and auxiliary solvents.

The construction of cluster-based crystalline chalcogenide structures through the traditional solvothermal method relies on synergistic control of precursors, template cations and auxiliary solvents. Generally, the combination of metal precursors plays a crucial role in controlling the size of clusters, while organic templates and auxiliary solvents usually contribute to the type of clusters and architecture of the framework. Decades of synthetic efforts have been mainly devoted to expanding organic amine templates for constructing new structures. However, the important role of auxiliary solvents in enriching the chalcogenide family is usually disregarded. Reported here are several new crystalline In-Se compounds (ISP-1 to 4) with different dimensions, obtained by elaborately regulating auxiliary solvents under the direction of the same organic template, piperidine. Of these four structures, ISP-1 is constructed by irregular supertetrahedral clusters, giving a novel 2D structure with a corner-shared single Se atom and In2Se3 five-member ring as linkers; ISP-2 has a 1D structure composed by interlinked In2Se3 five-member rings; ISP-4 is constructed by supertetrahedral T2 clusters exhibiting an uncommon zeolite-like mog network.

Controllable incorporation of 1,2,4-triazolate into cluster-based metal-chalcogenide frameworks.

The first incorporation of the 1,2,4-triazolate ligand into metal-chalcogenide semiconductor frameworks resulted in the formation of two new supertetrahedral-cluster-based triazolate frameworks (SCTFs) with hybrid inter-cluster connection modes, namely, SCTF-1 with an inorganic/organic linker ratio of 3 : 1 and SCTF-2 with a linker ratio of 2 : 2. The optical properties of these two close models were investigated.

Enhanced Water Dispersibility of Discrete Chalcogenide Nanoclusters with a Sodalite-Net Loose-Packing Pattern in a Crystal Lattice.

Good aqueous dispersibility of metal chalcogenide nanoclusters with an atomically precise structure is desirable to achieve tiny and uniform cluster-based "quantum dots". However, there are big challenges toward this goal, especially for the large-sized nanoclusters without covalently bonded organic ligands, because the strong electrostatic interactions between closely packed negatively charged nanoclusters and protonated organic amine templates in the crystal lattice impede the dispersion of cluster-based bulk crystalline samples. Here, we report two iso-structured crystalline metal chalcogenides composed of discrete supertetrahedral T4-MInS nanoclusters with the formulas of [M4In16S35]14- (denoted ISC-16-MInS, M = Zn and Fe), which adopt a sodalite-net loose-packing pattern in the crystal lattice and display superior dispersibility in water and some organic solvents as compared to other cases composed of the same type of nanoclusters with close-packing pattern. The dispersed T4-MInS nanoclusters were unexpectedly stabilized by adsorbing a certain number of H+ ions on surface S sites and simultaneously dropping partial surface S2- ions, instead of being surrounded by protonated organic amines, which was clearly verified by electrospray ionization mass spectrometry analysis. Notably, ISC-16-ZnInS behaves with superior performance on photodegradation of rhodamine B dye to ISC-16-FeInS. This is attributed to their difference in divalent-metal-directed separation efficiency of the photogenerated electrons and holes. This work holds great promise for the potential functional applications of uniformly dispersed semiconductor nanoclusters, such as cluster-based thin film devices, photoelectrodes, and photocatalysis.

Two Copper-Rich Open-Framework Chalcogenides Built from Unusual [Cu5(SnxM1-x)Se10] Clusters and [(SnxM1-x)2Se6] Dimeric Linkers (M = In and Ga).

Reported here are two unprecedented copper-rich open-framework chalcogenides constructed from unusual [Cu5(SnxM1-x)Se10] clusters and [(SnxM1-x)2Se6] dimeric linkers (M = In and Ga). The photoresponsive properties in the IR range and the photocatalytic activity for degradation of methylene blue dye of these two isostructural semiconductors were proved to be effectively adjusted by trivalent metal ions in a cluster.

New Insights into Mn-Mn Coupling Interaction-Directed Photoluminescence Quenching Mechanism in Mn2+-Doped Semiconductors.

Strong Mn-Mn coupling interactions (dipole-dipole and spin-exchange), predominantly determined by statistically and apparently short Mn···Mn distances in traditional heavily Mn2+-doped semiconductors, can promote energy transfer within randomly positioned and close-knit Mn2+ pairs. However, the intrinsic mechanism on controlling Mn2+ emission efficiency is still elusive due to the lack of precise structure information on local tetrahedrally coordinated Mn2+ ions. Herein, a group of Mn2+-containing metal-chalcogenide open frameworks (MCOFs), built from [Mn4In16S35] nanoclusters (denoted T4-MnInS) with a precise [Mn4S] configuration and length-variable linkers, were prepared and selected as unique models to address the above-mentioned issues. MCOF-5 and MCOF-6 that contained a symmetrical [Mn4S] core with a D2d point group and relatively long Mn···Mn distance (∼3.9645 Å) exhibited obvious red emission, while no room-temperature PL emission was observed in MCOF-7 that contained an asymmetric [Mn4S] configuration with a C1 point group and relatively short Mn···Mn distance (∼3.9204 Å). The differences of Mn-Mn dipole-dipole and spin-exchange interactions were verified through transient photoluminescent spectroscopy, electron spin resonance (ESR), and magnetic measurements. Compared to MCOF-5 and MCOF-6 showing a narrower/stronger ESR signal and longer decay lifetime of microseconds, MCOF-7 displayed a much broader/weaker ESR signal and shorter decay lifetime of nanoseconds. The results demonstrated the dominant role of distance-directed Mn-Mn dipole-dipole interactions over symmetry-directed spin-exchange interactions in modulating PL quenching behavior of Mn2+ emission. More importantly, the reported work offers a new pathway to elucidate Mn2+-site-dependent photoluminescence regulation mechanism from the perspective of atomically precise nanoclusters.

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.

Hierarchical heterostructure of SnO2 confined on CuS nanosheets for efficient electrocatalytic CO2 reduction.

The direct electroreduction of CO2 to ratio-tunable syngas (CO + H2) is an appealing solution to provide important feedstocks for many industrial processes. However, low-cost, Earth-abundant yet efficient and stable electrocatalysts for composition-adjustable syngas have still not been realized for practical applications. Herein, new hierarchical 0D/2D heterostructures of SnO2 nanoparticles (NPs) confined on CuS nanosheets (NSs) were designed to enable CO2 electroreduction to a wide-range syngas (CO/H2: 0.11-3.86) with high faradaic efficiency (>85%), remarkable turnover frequency (96.12 h-1) and excellent durability (over 24 h). Detailed experimental characterization studies together with theoretical calculations manifest that the ascendant catalytic performance is not only attributed to the heterostructure of ultrasmall SnO2 NPs homogeneously confined on ultrathin CuS NSs, which endows the maximum exposure of active sites and faster charge transfer, but is also accounted by the strong interaction between well-defined SnO2 and CuS interfaces, which modulated reaction free-energies of reaction intermediates and hence improved the activity of CO2 electroreduction to highly ratio-tunable syngas. This work provides a better understanding and a new strategy for intermediate regulation by interface engineering of hereostructures for CO2 reduction and beyond.

Molecular Modulation of a Molybdenum-Selenium Cluster by Sulfur Substitution To Enhance the Hydrogen Evolution Reaction.

Many strategies to optimize molybdenum selenide based electrocatalysts for hydrogen evolution reaction (HER) have been explored; however, the modulation of molybdenum selenide on the molecular scale remains an ongoing challenge. Here, we synthesized a new molecular HER electrocatalyst based on a molybdenum-selenium cluster (Mo3Se13) and further realized its modulation by precise sulfur substitution at the molecular level to enhance the HER activity. The density functional theory (DFT) calculations demonstrated that the substituted sulfur could promote the hydrogen adsorption process and thus improve the HER performance. This work not only realizes the selective replacement of the bridging selenium atom with a sulfur atom in the molybdenum-selenium cluster for the first time but also provides a precise model for illustrating the structure-property relationship in electrocatalysis on the molecular level.

Highly open chalcogenide frameworks built from unusual defective supertetrahedral clusters.

Enlarging the openess of chalcogenide frameworks is of significance for functionalizing semiconducting open frameworks, which are usually limited by their own interpenetration due to the rigid clusters and monotonous linkers. Herein, we report two zeolite-like chalcogenide open frameworks constructed from unusual defective supertetrahedral clusters and various kinds of linkers. Both the structures exhibit impressive architecture and high extra-framework volume ratios.

Light-triggered evolution of molecular clusters toward sub-nanoscale heterojunctions with high interface density.

Herein, we report a simple, yet highly effective approach for constructing a new type of sub-nanoscale ZnS/ZnO heterojunction (∼2-4 nm) with highly rich interfaces by photoetching hybrid Zn-S-O molecular clusters. The obtained ZnS/ZnO heterojunctions with ZnS spheres decorated with ultrasmall amorphous ZnO dots exhibit superior photocatalytic performance (∼94.0 µmol g-1 h-1), compared to nanoscale homologous samples obtained via conventional heat treatment (∼17.0-21.4 µmol g-1 h-1). Such a light-triggered molecular-cluster-to-heterojunction strategy provides a synthetic approach to building other sub-nanoscale hetero-structured materials for further promoting the catalytic-related applications.

Three new metal chalcogenide open frameworks built through co-assembly and/or hybrid assembly from supertetrahedral T5-InOS and T3-InS nanoclusters.

Reported here are three new metal chalcogenide open frameworks built from supertetrahedral [In35S52O8] (denoted as T5-InOS or o-T5) and [In10S20] (denoted as T3-InS) nanoclusters of different sizes and compositions via co-assembly and/or hybrid assembly modes. Such a set of cluster-based superlattices with dia topological structures clearly exhibit quantum size effects and electronic coupling interaction of adjacent nanoclusters, which can effectively explain that the band gap of the T3-(o-T5) hybrid-assembled material lies in the middle of T3-T3 and (o-T5)-(o-T5) co-assembled materials.

Two Penta-Supertetrahedral Cluster-Based Chalcogenide Open Frameworks: Effect of the Cluster Spatial Connectivity on the Electron-Transport Efficiency.

High-degree connectivity of clusters in open-framework chalcogenide semiconductors conceptually facilitates electron mobility between clusters; however, no direct evidence was obtained to prove the prediction because of the shortage of suitable structure models among such systems. Herein, two open-framework chalcogenides built from the same types of heterometallic P2-CuInSnS clusters but with different spatial connectivities of clusters were obtained, in which 3-connected clusters are assembled into a 3D framework with SrSi2 topology (MCOF-1) and 4-connected clusters (µ4-P2) are arranged into diamond topology (MCOF-2). Compared to MCOF-1, MCOF-2 exhibits a relatively rapid photocurrent response, good reproducibility, and high electrocatalytic oxygen reduction reaction activity. This work substantially demonstrates that cluster-based chalcogenide frameworks with higher-degree cluster connectivity possess faster electron-transport efficiency between adjacent clusters relative to low-connected ones with the same building units.

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 semiconducting metal-chalcogenide-organic framework with square-planar tetra-coordinated sulfur.

We demonstrated here a novel semiconducting metal-chalcogenide-organic framework (MCOF-89) with an optical bandgap through the unlikely assembly between a metal chalcogenide unit and carboxylic acid. The elusive metal-chalcogenide unit [Mn4(µ4-S)] with square-planar tetra-coordinated sulfur (sptS) is for the first time observed in MOFs.

Stable Supersupertetrahedron with Infinite Order via the Assembly of Supertetrahedral T4 Zinc-Indium Sulfide Clusters.

A new family member of T p, q-based hierarchical chalcogenide architecture was created by assembling regular T4-ZnInS clusters into a periodically "hollowed-out" cubic ZnS-type structure framework (T4,∞) via the cross-linker of the tetracoordinated corner µ4-S2-. Ion-exchange and CO2 adsorption experiments suggest that such a structure with a corner µ4-S2- linker has structural stability superior to those of previously reported chalcogenide open frameworks composed of the same T4-ZnInS clusters with a bicoordinated (µ2-S2-) or a tricoordinated (µ3-S2-) cross-linker. Importantly, this case further demonstrates the feasibility of systematically engineering stable porous crystalline chalcogenide frameworks by a "hollow-out" strategy.

Metal Chalcogenide Imidazolate Frameworks with Hybrid Intercluster Bridging Mode and Unique Interrupted Topological Structure.

Constructing a hybrid connection mode between cluster-based building blocks is of particular importance in the pursuit of fascinating framework structures. Reported here are two new metal chalcogenide imidazolate frameworks (SCIF-11 and SCIF-12) with a hybrid intercluster bridging mode and a unique interrupted topological structure. SCIF-11 has a typical dia topology with a T3-InS supertetrahedral cluster as the node and an imidazolate (IM) ligand as the linker, but it for the first time combines two kinds of intercluster connecting modes: T3-S-T3 and T3-IM-T3. Interestingly, SCIF-12 composed of T4-CdInS supertetrahedral clusters and IM ligands possesses a unique 3,4-connected interrupted framework with ins topology, with this being the first case in the family of cluster-based metal chalcogenide frameworks. This work provides a new strategy on enriching the intercluster bridging modes and topological types of metal chalcogenide frameworks.

Hybrid Assembly of Different-Sized Supertetrahedral Clusters into a Unique Non-Interpenetrated Mn-In-S Open Framework with Large Cavity.

Reported here is a unique crystalline semiconductor open-framework material built from the large-sized supertetrahedral T4 and T5 clusters with the Mn-In-S compositions. The hybrid assembly between T4 and T5 clusters by sharing terminal µ2-S2- is for the first time observed among the cluster-based chalcogenide open frameworks. Such three-dimensional structure displays non-interpenetrated diamond-type topology with extra-large nonframework volume of 82%. Moreover, ion exchange, CO2 adsorption, as well as photoluminescence properties of the title compound are also investigated.

Nonlinear Variation in the Composition and Optical Band Gap of an Alloyed Cluster-Based Open-Framework Metal Chalcogenide.

Unexpected nonlinear variation in the composition and optical band gap was observed in an alloyed open-framework metal chalcogenide composed of supertetrahedral clusters. A tentative hypothesis was proposed to explain how the title compound [In28Se54(H2O)4]·24H+-PR· nH2O (PR = piperidine) exhibits a limitation in the S-alloying level and a large variation in the optical band gap.

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

The highly efficient and cheap non-Pt-based electrocatalysts such as transition-based catalysts prepared via facile methods for oxygen reduction reaction (ORR) are desirable for large-scale practical industry applications in energy conversion and storage systems. Herein, we report a straightforward top-down synthesis of monodisperse ultrasmall manganese-doped multimetallic (ZnGe) oxysulfide nanoparticles (NPs) as an efficient ORR electrocatalyst by simple ultrasonic treatment of the Mn-doped Zn-Ge-S chalcogenidometalate crystal precursors in H2O/EtOH for only 1 h at room temperature. Thus obtained ultrasmall monodisperse Mn-doped oxysulfide NPs with ultralow Mn loading level (3.92 wt %) not only exhibit comparable onset and half-wave potential (0.92 and 0.86 V vs reversible hydrogen electrode, respectively) to the commercial 20 wt % Pt/C but also exceptionally high metal mass activity (189 mA/mg at 0.8 V) and good methanol tolerance. A combination of transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical analysis demonstrated that the homogenous distribution of a large amount of Mn(III) on the surface of NPs mainly accounts for the high ORR activity. We believe that this simple synthesis of Mn-doped multimetallic (ZnGe) oxysulfide NPs derived from chalcogenidometalates will open a new route to explore the utilization of discrete-cluster-based chalcogenidometalates as novel non-Pt electrocatalysts for energy applications and provide a facile way to realize the effective reduction of the amount of catalyst while keeping desired catalytic performances.