In Situ Anchoring Polymetallic Phosphide Nanoparticles within Porous Prussian Blue Analogue Nanocages for Boosting Oxygen Evolution Catalysis.

The controllable synthesis of metal-based nanoclusters for heterogeneous catalytic reactions has received considerable attention. Nevertheless, manufacturing these architectures, while avoiding aggregation and retaining surface activity, remains challenging. Herein, for the first time we designed NiCoFe-Prussian blue analogue (PBA) nanocages as a support for in situ dispersion and anchoring of polymetallic phosphide nanoparticles (pMP-NPs). Benefiting from the porous surfaces and the synergistic effects between pMP-NPs and the cyano groups in PBA, the NiCoFe-P-NP@NiCoFe-PBA nanocages exhibit a significantly enhanced catalytic activity for oxygen evolution reaction (OER) with an overpotential of 223 mV at 10 mA cm-2 and a Tafel slope of 78 mV dec-1, outperforming the NiCoFe-PBA nanocubes, NiCoFe-P nanocages, NiFe-P-NP@NiFe-PBA nanocubes, and CoFe-P-NP@CoFe-PBA nanoboxes. This work not only offers the synthesis strategy of in situ anchoring pMP-NPs on PBA nanocages but also provides a new insight into optimized Gibbs free energy of OER by regulating electron transfer from metallic phosphides to PBA substrate.

Synthesis, Crystal Structure, Electronic Structure, and Electrocatalytic Hydrogen Evolution Reaction of Synthetic Perryite Mineral.

Recently, it has been reported that the enstatite chondrite (EC) meteorite may contain enough hydrogen to provide a plausible explanation for water's initial existence on Earth. Perryite mineral is one of the key components of EC, but its detailed chemical composition and phase width remain elusive compared with other minerals found in EC. Therefore, we embark on a series of investigations of the synthesis, crystal structure, and electronic structure of the synthetic perryite mineral (NixFe1-x)8(TyP1-y)3 (T = Si and Ge; 1 ≥ x, y ≥ 0). Its crystal structures were established based on single-crystal and powder X-ray diffraction techniques. It is realized that its structural and phase stabilities are highly dependent on the nature of the doping element (i.e., Fe and Si). The inclusion of Si and Fe elements can greatly alter the bonding scheme near the Fermi level (Ef), which is vital to the phase stability and accounts for the chemical composition of the natural perryite mineral (quaternary compound) in EC meteorites. Furthermore, this phase exhibits good electrocatalytic activity toward the hydrogen evolution reaction (HER). The best and the worst HER performances are for the Ni8Ge2P and Ni8Si2P samples, respectively, which suggests that the long bond length and high polarity of the covalent bond are the preferred criteria to enhance the electrocatalytic HER in this series.

A novel promising infrared nonlinear optical selenide KAg3Ga8Se14 designed from benchmark AgGaQ2 (Q = S, Se).

Obtaining fresh nonlinear optical (NLO) materials is an attractive and challenging topic for the development of laser techniques. Using benchmark AgGaQ2 (Q = S, Se) as the template, new KAg3Ga8Se14 is obtained by a solid-state reaction. Its structure can be built by the intergrowth of 2 : 1 AgGaSe2 and Ga2Se3-like slabs if the K site is occupied by Ag. Powdery KAg3Ga8Se14 demonstrates moderate phase-matchable NLO responses, and a LDT of ca. 2 × AgGaS2. DFT calculations reveal that both AgSe4 and GaSe4 tetrahedral motifs contribute a lot to the NLO performance. This work reveals a new class of promising infrared NLO materials, and the design strategy may apply to other systems.

Lanthanide contraction regulates the HER activity of iron triad intermetallics in alkaline media.

In this work, we have systematically investigated the HER activity of the RE2Co17 (RE = Y, Pr, Gd, Tb, Ho and Er) series and revealed that their HER activities are highly correlated with the averaged Co-Co bond length of each compound. The HER performance follows the order of Gd2Co17 > Tb2Co17 > Pr2Co17 > Y2Co17 > Ho2Co17 > Er2Co17. This suggests that the unique feature of rare-earth metals, lanthanide contraction, can effectively alter the interatomic spacing and impact the corresponding HER activity. Additionally, Gd2Fe17 and Gd2Ni17 with different d electron density in the system were synthesized and comparison of their HER efficiencies is also discussed. Gd2Ni17 demonstrates the highest HER efficiency among all samples, and it only requires an overpotential (η) of 44 mV to acquire a current density of 10 mA cm-2. The theoretical calculation offers a clue that the H adsorption energy (GHad) for H atoms on Ni is lower than that on Co and Fe due to the high electron population in the antibonding state of the Ni atom. This well explains the origin of the synergistic effect for the high electrocatalytic HER of these iron triad intermetallics.

Electronic structure inspired a highly robust electrocatalyst for the oxygen-evolution reaction.

We demonstrated that the electronic-band structure holds the key to electrocatalytic durability towards the oxygen-evolution reaction (OER). Density functional theory (DFT) revealed the characteristic of Ni-Ni bonding interactions within Ni5P4, Ni5P2 and Ni3P were different and could influence their phase stabilities during the OER. Ni5P2 and Ni3P exhibited very robust OER performances at high current density (>350 mA cm-2) over 12 h whereas, for Ni5P4, obvious deterioration was observed. In situ/ex situ X-ray near-edge structure, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy indicated the phase stability of Ni5P4, Ni5P2 and Ni3P behaved differently during the OER. These materials transformed to Ni oxyhydroxide but the process for Ni5P2 and Ni3P was much slower even under high anodic potential 1.6 V (V vs. RHE). These results supported the theoretical prediction and provide a refreshing viewpoint for designing reliable electrocatalysts for the OER.

Second-Order Nonlinear-Optical-Active Selenide Borate YSeBO2: Featuring a [YSeBO2]n Planar Belt.

Chalcogenide borates were very rarely investigated in the past. As the second selenide borate, YSeBO2 obtained by a high-temperature solid-state reaction crystallizes in the noncentrosymmetric orthorhombic space group Cmc21 with a novel structure type. Its structure consists of two basic building units, [BO3]3- planar triangles and [YO3Se4]11- pentagonal bipyramids, and features the [YSeBO2]n planar belt. Second-harmonic-generation measurement shows its phase-matchable activity. YSeBO2 has an optical energy gap of 3.45 eV. Density functional theory calculation is also performed, addressing the electronic structure and nonlinear-optical property.

Hexagonal In2Se3: A Defect Wurtzite-Type Infrared Nonlinear Optical Material with Moderate Birefringence Contributed by Unique InSe5 Unit.

The balance between second harmonic generation (SHG) intensity and laser-induced damage threshold (LIDT), together with phase-matchable behavior, is the key point for exploration of novel nonlinear optical (NLO) materials. In this work, the NLO property of defect wurtzite-type hexagonal-In2Se3 (γ) is extensively explored first. It exhibits a strong SHG intensity of 2.6 × AgGaS2 (AGS) at 2.1 µm, and a high powder LIDT of 7.3 × AGS. From wurtzite to γ-In2Se3, the birefringence changes from 0.003 to 0.075, resulting in the phase-matchable phenomenon of γ-In2Se3. This is well ascribed to the contribution of the unique InSe5 unit in γ-In2Se3 from the result of birefringence calculation and analysis.

Designing Sulfide Borate as a Novel Type of Second-Order Nonlinear-Optical Material.

Designing second-order nonlinear-optical (NLO) materials with new structures is an attractive topic. Here, a novel type of sulfide borate, Eu2B5O9S, and one of its derivatives combining S2-, I-, and borate anions in one structure (three in one), viz., Eu4.5(B5O9)2SI, are designed and synthesized with a high-temperature solid-state method. They crystallize in the noncentrosymmetric space group Pnn2. As the first sulfide borate being NLO-active, Eu4.5(B5O9)2SI demonstrates good NLO behavior, namely, a moderate powder NLO response of ca. 0.5 times and a high laser-induced damage threshold (LIDT) of ca. 15 times those of AgGaS2, and is phase-matchable. The design strategy and experimental results are verified and explained by density functional theory calculations.

Enhanced Electrochemiluminescence of Porphyrin-Based Metal-Organic Frameworks Controlled via Coordination Modulation.

Precise control over the composition, morphology, and size of porphyrin-based metal-organic frameworks is challenging, but the extension of these hybrid materials will enable the creation of novel electrochemiluminescence (ECL) emitters. The coordination of various entities is made from Zn2+ ions and meso-tetra(4-carboxyphenyl)porphine (TCPP), modulated by both solvent and bathophenanthrolinedisulfonic acid disodium salt (BPS) as capping agent, resulting in limited crystal growth of Zn-TCPP in DMF/H2O (v/v, 1:1) and the formation of nanoscale TCPP-Zn-BPS. The role of BPS is also evaluated using Zn-TCPP and BPS-Zn-TCPP as controls, prepared in the absence of BPS and different coordinating sequences of ligands, respectively. The newly obtained TCPP-Zn-BPS exhibits a variety of different morphologies, as well as spectral and optoelectronic properties. The ECL behavior of TCPP-Zn-BPS is investigated by using H2O2 as co-reactant. The amplification of ECL is further studied by ECL spectroscopies and cyclic voltammetry, with the corresponding mechanism proposed.

Intermetallic compounds with high hydrogen evolution reaction performance: a case study of a MCo2 (M = Ti, Zr, Hf and Sc) series.

Noble metals (e.g., Ru, Ir and Pt) or their derivatives exhibit very appealing activity toward the hydrogen evolution reaction (HER), but their high price and low reserves impede their wide use. Herein, we propose a strategy in which, through the manipulation of crystal and electronic structure, one can convert a common metal to have a Pt-like performance for HER. To achieve this goal, a series of MCo2 (M = Ti, Zr, Hf and Sc) has been synthesized by using a rapid arc-melting method. TiCo2 exhibits comparable HER activity to that of Pt/C, for which it requires only -70 mV (V vs. RHE) to reach 10 mA cm-2 with a Tafel slope of 33 mV decade-1 in 1.0 M KOH. Moreover, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) indicate that the lower adsorption energy (ΔGH*) of H on the Co atom in TiCo2, due to the change in Co electronic state, is another key factor to account for its high HER activity. This case study offers a good illustration of how to transform a non-noble metal so it behaves like a noble metal toward HER and can potentially be applied under other conditions.

Triple-Kagomé-Layer Slabs of Mixed-Valence Rare-Earth Ions Exhibiting Quantum Spin Liquid Behaviors: Synthesis and Characterization of Eu9MgS2B20O41.

We prepared a new rare-earth compound, Eu9MgS2B20O41 (EMSBO), and characterized its structural and physical properties. EMSBO consists of triple-Kagomé-layer slabs separated by nonmagnetic ions and groups. Within each slab, intervalence charge transfer has been found to occur between the Eu2+ and Eu3+ Kagomé layers, a new channel for quantum fluctuation of magnetic moments. The measured magnetic susceptibilities and the specific heat capacity exhibit very similar features characteristic of quantum spin liquid behaviors observed in other materials.

Large Second Harmonic Generation (SHG) Effect and High Laser-Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2 Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59-25 µm is also significantly wider than that of AGS (ca. 0.48-≈11.4 µm). The occurrence of the strong SHG responses and good phase-matching indicate that the structure of the new Ga2 Se3 phase can only be non-centrosymmetric and have a lower symmetry than the cubic γ-phase. The observed excellent SHG and phase-matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Balanced Second-Order Nonlinear Optical Properties of Adducts CHI3·(S8)3 and AsI3·(S8)3: A Systematic Survey.

Two isostructural adducts CHI3·(S8)3 (1) and AsI3·(S8)3 (2) are synthesized by a simple solution method. Both of them crystallize in noncentrosymmetric R3 m, featuring van der Waals interaction linked CHI3 tetrahedra or SbI3 trigonal pyramids with crown-like S8 molecules. Both 1 and 2 show strong SHG responses and phase matchability under either 1.064 or 2.1 µm. The results of DFT calculations indicate that the electron transfer happens from S-3p to I-5p orbitals, and both of them demonstrate indirect band gaps. The NLO effects of 1 and 2 are almost fully contributed from the CHI3 or AsI3 units. Compared with AgGaS2, their powder laser damage thresholds are ca. 15 and 51 times higher.

Transition Metal Free Monoclinic Eu8In17.33S34 and Its Anisotropic Photoelectronic Responses.

Novel Eu8In17.33S34 (1) is obtained by a solid state reaction and its structure features three parallel slabs of [In9.33S18]∞, [Eu8]∞, and [In8S16]∞, together with defects in specific lattice sites. It is the first monoclinic ternary M8- mIn18- n Q34 ( M = Pb, Sn, Eu; Q = S, Se) phase member, and the modulation from the ultralong In-S bond and lattice site with strong antibonding effect results in the unique structure feature. Its single crystals show anisotropic conductivity and photoconductivity.

The first investigation of europium silicate melilite for second-order nonlinear optical application: experimental and theoretical studies.

A europium pyrosilicate, Eu2MgSi2O7 (1), is obtained using a high-temperature solid-state reaction. It crystallizes in the tetragonal noncentrosymmetric space group P4[combining macron]21m, and its structure features a 2D structure built by SiO4 and MgO4 tetrahedra, resulting in interlayer cavities occupied by Eu2+ ions. It has a SHG intensity around 0.7 times that of KTP in the particle size range of 45-75 µm under 2.1 µm radiation, demonstrating a relatively strong effect among the silicates. A typical photoluminescence phenomenon of Eu2+ can be observed at 482 nm. Calculations on the electronic structure and optical properties of 1 are performed. Moreover, to discuss the potential of pyrosilicates and related compounds as NLO crystals, the theoretical analysis on other A2BM2O7 compounds is also addressed.

Adduct-Type IR Nonlinear-Optical Crystal SbI3·(S8)3 with a Large Second-Harmonic Generation and a High Laser-Induced Damage Threshold.

A noncentrosymmetric adduct, SbI3·(S8)3, is obtained by a facile solution method. It crystallizes in the trigonal space group R3 m, and its structure features van der Waals force connected, isolated trigonal-pyramidal SbI3 and chairlike S8 units. SbI3·(S8)3 exhibits strong second-harmonic-generation responses around 4 times that of KH2PO4 (1.064 µm) and 1 times that of AgGaS2 (AGS; 2.1 µm) at 210-250 µm, respectively. Under both laser-radiation wavelengths, it exhibits type I phase-matching behavior. Its laser-induced damage threshold is measured to be around 26 times that of AGS under 1.064 µm. To better understand these optical data, theoretical calculations are performed to address its electronic structure and optical properties.

SnI4 ⋠(S8 )2 : A Novel Adduct-Type Infrared Second-Order Nonlinear Optical Crystal.

A simple adduct from tin tetraiodide SnI4 and octasulfur S8 , SnI4 ⋅(S8 )2 (1), is obtained employing a facile reaction. The combination of Sn4+ ions with d10 electron configuration, acentric SnI4 tetrahedra, and lone-pair effects of S8 , makes 1 a phase-matchable infrared NLO crystal with a moderate second-harmonic generation (SHG) response and a very high laser-induced damage threshold (LIDT), which is well confirmed by the DFT calculations.

Crystal Chemistry and Photocatalytic Properties of RE4S4Te3 (RE = Gd, Ho, Er, Tm): Experimental and Theoretical Investigations.

Reported are the synthesis and structural characterization of a new series of ternary rare-earth mix-chalcogenides RE4S4Te3 (RE = Gd, Ho, Er, Tm) that have been obtained from high-temperature solid state reactions. These compounds crystallize in Ho4S4Te2.68 structure types with monoclinic C2/ m and/or orthorhombic Immm space groups. The space group variation within this series is due to the position disorder along the Te plane (Te to TeA and TeB). The structural relationship and change between these two space groups are analyzed. It is realized that these compounds are all photocatalytic active under simulated sunlight. The trend of their photocatalytic activities and photocurrent responses is well-explained by using theoretical calculation as well as dipole moment analysis.

Fe3S4 Nanoparticles Wrapped in an rGO Matrix for Promising Energy Storage: Outstanding Cyclic and Rate Performance.

Iron sulfides/oxides/fluorides have been profoundly investigated as electrodes for rechargeable batteries recently in view of their high-theory capacities, low cost, and environmentally benign nature. Here, Fe3S4 nanoparticles (NPs) wrapped in reduced graphene oxide (Fe3S4 NPs@rGO) have been obtained using a simple one-pot hydrothermal approach, which is characterized using various techniques. As the anode for Li-ion batteries, Fe3S4 NPs@rGO displays a reversible discharge capacity of 950 mA h/g after 100 cycles at 0.1 A/g, and 720 mA h/g capacity can be achieved after 800 cycles even at 1 A/g. Even at 10 A/g, 462 mA h/g capacity can be maintained. The excellent electrochemical properties for Fe3S4 NPs@rGO can be ascribed to a collaborative effect between Fe3S4 NPs and an rGO matrix, which possess high Li-ion storage ability and excellent conductivity, respectively.

Sm3S3BO3: The First Sulfide Borate without S-O and B-S Bonds.

An unprecedented quaternary sulfide borate, Sm3S3BO3 (1), was obtained via a high-temperature solid-state synthesis method. It crystallizes in the triclinic space group P1̅, and its 3D structure features a 2D (Sm2S2)∞ wrinkled layer and a 1D (SmS)∞ ladderlike chain bridged by trigonal-planar (BO3)(3-) through Sm-O bonds, demonstrating the first sulfide borate without S-O and B-S bonds. Its optical energy gap is measured to be around 2.5 eV and verified by electronic structure calculation.