Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction.

Metal-organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm-2 and a Tafel slope of 54.44 mV dec-1. Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm-2.

Linear π-conjugated units of the D∞h point group as superior ultraviolet birefringent units.

At present, birefringent materials face a limited selection of large structural anisotropic functional modules (FMs). In this paper, we present a series of linear units which belong to the D∞h point group represented by (BO2)- proposed as novel birefringent active FMs. By analyzing the molecular orbital of the (BO2)- unit, it is found that there are relatively fewer non-bonding orbitals in (BO2)- than in (BO3)3- and the delocalized π bonds in (BO2)- appear in shallow energy levels, which are easily excited. Through first-principles modeling and simulation, it is found that the delocalized π bonds in (BO2)- can still show obvious transition processes, which produce a significant gain to the birefringence. Besides, a series of compounds containing linear anionic frameworks which also belong to the D∞h point group show excellent optical anisotropy in the same way. Therefore, the linear anionic basic units which belong to the D∞h point group have the great potential to become new birefringent FMs.

MM'B3O4F3 (M = K; M' = Na, K, Cs): Alkali-Metal Fluorooxoborates with ∞1[B3O4F3] Chains and Deep-Ultraviolet Cutoff Edges.

Three mixed-alkali-metal fluorooxoborates, KNaB3O4F3 (I), K2B3O4F3 (II), and KCsB3O4F3 (III), were acquired in a closed system. I-III are isomorphic and adopt orthorhombic structures [Pbcn (No. 60)] with wavy parallelly arranged pseudolayers composed of ∞1[B3O4F3] chains, which exhibit slight differences in the arrangement modes of the fundamental building blocks. First-principles calculations illustrate that they all have moderate birefringence and large band gaps on the order of 7.0 eV, suggesting deep-ultraviolet (DUV) cutoff edges. In order to investigate the main source of the optical properties, the electronic structure and anisotropy of the response electron distribution were analyzed. Experimental characterizations for I confirm the structure and DUV transparence ability.

Ag4SnGe2S7: A Noncentrosymmetric Chalcogenide in I4-II-IV2-VI7 System with Non-Diamond-Like Structure Featuring 1D ∞[SnGe2S8]6- Infinite Chain.

The I4-II-IV2-VI7 metal chalcogenide system has become an attractive research system because of its excellent physical and chemical properties. Here, we report the discovery of a new SnII-based quaternary chalcogenide in the I4-II-IV2-VI7 system, Ag4SnGe2S7, with a non-diamond-like structure and crystallizing in the Cc space group. The compound is characterized by isolated pyramid-like [SnS3] units and one-dimensional ∞[SnGe2S8]6- infinite chains with two orientations formed by the corner-sharing connected [SnGe2S8]6- units. It has a band gap of 2.40 eV and is insensitive to air and moisture.

Surface Plasmon Resonance Boost Electrocatalytic Alcohol Oxidation over Three-Dimensional PdM (M = Au, Ag, Cu) Nanosheet Assemblies.

Photoelectrocatalytic nanomaterials are promising for direct alcohol fuel cells, but the construction of high-efficiency catalysts remains difficult. We herein successfully synthesized three-dimensional (3D) PdM nanosheet assemblies (PdM NSAs, M = Au, Ag, and Cu) through a seed-mediated growth method, which displayed a typical 3D nanoflower morphology assembled from many two-dimensional ultrathin nanosheets. Due to the open 3D structure and the synergistic and electronic effects between Pd and Ag, the optimized PdAg NSAs showed the highest mass activity (9378 mA mg-1) for the ethylene glycol oxidation reaction. More interestingly, when irradiated with visible light, the mass activity increased to 14 590 mA mg-1, 12.1 times higher than that of the commercial Pd/C (1205 mA mg-1). In addition, the as-obtained catalysts also showed better long-term durability than that of the commercial Pd/C under the condition of with or without visible-light illumination. This work highlights the utilization of light energy in designing excellent photoelectrocatalysts to promote the photoelectrocatalytic performance of anode catalysts for fuel cells.

One-pot synthesis of 3D surface-wrinkled PdAu nanospheres for robust alcohols electrocatalysis.

Three dimensional (3D) noble-metal nanomaterials with special surface structures have been regarded as high-performance catalysts for alcohol oxidation on account of their superior thermal stability, electrical conductivity and large specific surface area. Although extensive efforts have been devoted to the preparation of 3D Pd-based catalysts with superior activity and stability, designing a simple, effective and eco-friendly method remains a challenge. Herein, we developed a facile one-step coreduction strategy to synthesize a series of 3D surface-wrinkled PdAu nanospheres (NSs) with tunable Pd/Au atomic ratios and found a universal method to prepare surface-wrinkled PdM (M = Au, Pt, Cu and Pb) NSs. Benefiting from the function of the surfactant cetyltrimethylammonium chloride (CTAC), the synthesized PdAu NSs with different composition possess abundant surface wrinkles, which is beneficial for exposing more electroactive centers. Attributed to the unique geometric morphology and optimized atomic ratio, the PdAu-2 NSs exhibited an optimal mass activity (MA) of 8103 mA mg-1 and 5113 mA mg-1 for the ethylene glycol oxidation reaction (EGOR) and ethanol oxidation reaction (EOR), which was 6.1 and 4.1 times that of commercial Pd/C, respectively. Moreover, the PdAu-2 NSs exhibited superb stability after long-term current-time (i-t) and cyclic voltammetry (CV) tests of the EGOR and EOR. This work not only provides new avenues to engineer PdAu NSs with enhanced electrocatalytic performance but also offers guidance for extending to more 3D PdM (M = other metals) NSs with novel morphology applied to fuel cell fields.

Rb2CdSi4S10: novel [Si4S10] T2-supertetrahedra-contained infrared nonlinear optical material with large band gap.

Infrared nonlinear optical (IR-NLO) materials with wide band gaps are important for generating high-power laser light for modern laser technologies. Herein, a wide band gap IR-NLO material, Rb2CdSi4S10, was rationally designed and fabricated by introducing a NLO-active [Si4S10] T2-supertetrahedron (ST) into the quaternary sulfide system. The Rb2CdSi4S10 shows the largest band gap (4.23 eV) among the quaternary chalcogenide IR-NLO materials reported, which results in a high laser-induced damage threshold (LIDT) of ∼5 × AgGaS2 (AGS) at 1064 nm. At the same time, it has a moderate second-harmonic generation (SHG) response (0.6 × AGS). Based on statistical analyses, the Rb2CdSi4S10 is the first compound to be discovered in the AI2BIICIV4QVI10 family, and also the first Si-rich sulfide IR-NLO material with a [Si4S10] T2-supertetrahedra. The results indicate that Rb2CdSi4S10 is a promising new IR-NLO material, and the NLO-active [Si4S10] T2-ST unit could be used for the exploration of IR-NLO material with excellent performances.

In situ phosphoselenization induced heterointerface engineering endow NiSe2/Ni2P/FeSe2 hollow nanocages with efficient water oxidation electrocatalysis performance.

Exploiting Earth-abundant and highly effective electrocatalysts toward the oxygen evolution reaction (OER) is critical for boosting water splitting efficiency. Herein, we proposed a novel in situ phosphoselenization strategy to fabricate heterostructured NiSe2/Ni2P/FeSe2 (NiFePSe) nanocages with a modified electronic structure and well-defined nanointerfaces. Owing to the strong interfacial coupling and synergistic effect among the three components, the prepared NiFePSe nanocages exhibit superior OER performance with an ultralow overpotential of 242 mV at 10 mA cm-2 and a small Tafel slope of 55.8 mV dec-1 along with robust stability in 1 M KOH. Remarkably, the highly open 3D porous architecture, delicate internal voids, and numerous surface defects endow the NiFePSe nanocages with abundant active sites and enhanced electron mobility. In addition, the super-hydrophilic surface is conducive to facilitating mass transfer between the electrolyte and electrode and rapidly releasing the bubbles. This work may lead to new breakthroughs in the tuning of multi-component transition metal catalysts and the designing of highly active and durable materials for water splitting.

Rapid synthesis of Palladium-Platinum-Nickel ultrathin porous nanosheets with high catalytic performance for alcohol electrooxidation.

Bimetallic two-dimensional (2D) nanomaterials are widely used in electrocatalysis owing to their unique physicochemical properties, while trimetallic 2D materials of porous structures with large surface area are rarely reported. In this paper, a one-pot hydrothermal synthesis of ternary ultra-thin PdPtNi nanosheets is developed. By adjusting the volume ratio of the mixed solvents, PdPtNi with porous nanosheets (PNSs) and ultrathin nanosheets (UNSs) was prepared. The growth mechanism of PNSs was investigated through a series of control experiments. Notably, thanks to the high atom utilization efficiency and fast electron transfer, the PdPtNi PNSs have remarkable activity of methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). The mass activities of the well-tuned PdPtNi PNSs for MOR and EOR were 6.21 A mg-1 and 5.12 A mg-1, respectively, much higher than those of commercial Pt/C and Pd/C. In addition, after durability test, the PdPtNi PNSs exhibited desirable stability with the highest retained current density. Therefore, this work provides a significant guidance for designing and synthesizing a new 2D material with excellent catalytic performance toward direct fuel cells applications.

Photoelectrocatalytic oxidation of ethylene glycol on trimetallic PdAgCu nanospheres enhanced by surface plasmon resonance.

The notable surface plasmon resonance (SPR) effect of some metals has been applied to improve the efficiency of alcohol oxidation reactions, whereas the comprehensive investigation of Cu-assisted photoelectrocatalysis remains challenging. We herein successfully prepared trimetallic PdAgCu nanospheres (NSs) with abundant surface bulges for the advanced ethylene glycol oxidation reaction (EGOR) and compared them with bimetallic PdAg NSs to investigate the performance enhancement mechanism. Impressively, the as-optimized PdAgCu NSs exhibited superb mass activity and electrochemical stability. Moreover, under visible light illumination, the mass activity of PdAgCu NSs increased to 1.62 times compared to that in the dark, and in contrast, the mass activity of PdAg NSs only increased to 1.48 times that in the dark. A mechanistic study indicated that the incorporation of Cu not only strengthens the whole SPR effect of PdAgCu NSs but also further modifies the electronic structure of Pd. This work highlighted that the incorporation of Cu into PdAg NSs further enhanced the photoelectrocatalytic performance and increased noble metal atom utilization, which may provide guidance to fabricate novel and promising nanocatalysts in the field of photoelectrocatalysis.

Heterostructure engineering and ultralow Pt-loaded multicomponent nanocage for efficient electrocatalytic oxygen evolution.

Developing highly efficient electrocatalysts based on appropriate heterojunction engineering and electronic structure modification for the oxygen evolution reaction (OER) has been extensively recognized as an effective approach to increase the efficiency of water splitting. Herein, ultralow Pt-loaded (1 %) NiCoFeP@NiCoFe-PBA hollow nanocages with well-defined heterointerfaces and modified electronic environment are successfully fabricated. As expected, the obtained Pt-NiCoFeP@NiCoFe-PBA exhibits outstanding performance with a low overpotential of 255 mV at 10 mA cm-2 and a small Tafel slope of 57.2 mV dec-1. More specifically, the highly open three-dimensional structure, exquisite interior voids and abundant surface defects endow Pt-NiCoFeP@NiCoFe-PBA nanocages with more electrochemical active sites. Meanwhile, experimental results and mechanism studies also reveal that the construction of heterogeneous interfaces as well as incorporation of noble metals could readily induce strong synergistic effects and significantly tailor electronic configurations to optimize the binding energy of the intermediates, thereby achieving prominent OER performance.

Na2SrB16O26: a new borate with independent interpenetrating B-O networks and deep-ultraviolet cutoff edge.

A new borate, Na2SrB16O26, was synthesized by the high-temperature solution method. It exhibits complicated interpenetrating 3D B-O frameworks composed of the functional building block (FBB) [B8O16]. The UV-vis-NIR diffuse reflectance spectroscopy shows that it has a deep-ultraviolet (DUV) cutoff edge (<200 nm). The relationship between the structures and optical properties was uncovered by theoretical calculations. By the first-principles calculation, the birefringence is estimated to be 0.07 at 1064 nm. The response electron distribution anisotropy (REDA) analysis indicates that the [BO3] units contribute mainly to the generation of the moderate birefringence.

LiSrSbS3: parallel configurations of lone pair electrons inducing a large birefringence.

Enhancement of birefringence is significant since the birefringent materials can create and control polarized light and be used extensively in various advanced optical systems. By optimizing the arrangement of [SbS3] units with stereo-chemical active lone pair electrons, a new quaternary thioantimonate LiSrSbS3 with a large birefringence has been successfully synthesized by a high temperature solid-state reaction method. LiSrSbS3 crystallizes in the monoclinic space group of P21/c. In the structure, the isolated infinite [LiS4] chains and zigzag [SrS6] chains are alternately connected with each other to compose a three-dimensional (3D) framework, and the isolated pyramid [SbS3] units are located between them. To analyze the source of large birefringence, the electronic structure and optical properties of LiSrSbS3 were further investigated by the first-principles method, and the results show that the optimized arrangement [SbS3] trigonal pyramid induces a large birefringence.

Defect and Interface Engineering of Three-Dimensional Open Nanonetcage Electrocatalysts for Advanced Electrocatalytic Oxygen Evolution Reaction.

Defect engineering and interface engineering are two efficient approaches to promote the electrocatalytic performance of transition metal oxides (TMOs) by modulating the local electronic structure and inducing a synergistic effect but usually require costly and complicated processes. Herein, a facile electrochemical etching method is proposed for the controllable tailoring of the defects in a three-dimensional (3D) open nanonetcage CoZnRuOx heterostructure via the in situ electrochemical etching to remove partial ZnO. The highly open 3D nanostructures, numerous defects, and multicomponent heterointerfaces endow the CoZnRuOx nanonetcages with more accessible active sites, moderated local electronic structure, and strong synergistic effect, thereby enabling them to not only deliver an ultralow overpotential (244 mV @ 10 mA cm-2) for oxygen evolution reaction (OER) but also high-performance overall water electrolysis by coupling with commercial Pt/C, with a potential of 1.52 V at 10 mA cm-2. Moreover, experiments and characterizations also reveal that the remaining Zn2+ can facilitate OH- adsorption and charge transfer, which also further improves the electrocatalytic OER performance. This work proposes a promising strategy for creating surface defects in heterostructured TMOs and provides insights to understand the defect- and interface-induced enhancement of OER electrocatalysis.

Rich grain boundaries endow networked PdSn nanowires with superior catalytic properties for alcohol oxidation.

Networked nanowire (NNW)-structured catalysts have attracted extensive attention due to their large surface area and structural stability, which mean that they have excellent catalytic activity and stability and can be used as anode reaction catalysts for use in direct alcohol fuel cells (DAFCs). Herein, a series of networked PdSn nanowires synthesized via a modified polyol strategy are used as efficient DAFCs anode reaction catalysts. The introduction of Sn plays an important role in the improvement of catalytic behavior, in which the existence of Sn promotes the oxidation of intermediates by providing abundant oxyphilic species. Moreover, the generated PdSn NNWs-3 with optimal content show rich grain boundaries and an even NNW structure, which provides more active sites to further improve catalytic performance, so it exhibits excellent activity toward alcohol oxidation. The mass activities of PdSn NNWs-3 toward the ethanol oxidation reaction (EOR) and the methanol oxidation reaction (MOR) are 8105.0 and 3099.5 mA mgPd-1, which are 6.9 and 10.7 times higher than those of Pd/C, respectively. Compared with Pd/C, the PdSn NNWs also display enhanced stability towards the EOR and MOR. This work demonstrates that NNW nanocatalysts indeed exhibit excellent catalytic performance for alcohol oxidation reactions.

A new broad-band infrared window material CdPbOCl2 with excellent comprehensive properties.

Herein, a new IR window material CdPbOCl2 is rationally designed and fabricated by a heavy-metal oxide and halide combined strategy. The millimeter-scale CdPbOCl2 single crystal exhibits a wide IR transparent region (1.4-18.0 µm) and excellent comprehensive properties. The results provide an insight into the exploration of broad-band IR window materials.

Design and synthesis of Ba3SiSe5 with suitable birefringence modulated via MIV atoms in the Ba-MIV-Q (MIV = Si, Ge; Q = S, Se) system.

A new ternary Ba-based selenide, Ba3SiSe5, was synthesized by a high-temperature solid-state method. It crystallizes in the centrosymmetric space group Pnma (no. 62) of the orthorhombic system. The structure of the title compound consists of unique Se(4)Ba layers and discrete SiSe4 tetrahedra. The structure and computational properties of Ba3SiSe5 are systematically studied together with those of the Ba-MIV-Q (MIV = Si, Ge; Q = S, Se) system, and show an interesting difference in dimensions formed by one of the crystallographic Ba atoms and MIVQ4 tetrahedra, as well as optical property transformations modulated by MIV atoms. First principles methods were employed to obtain a better understanding of the relationship between structures and properties. Ba3SiSe5 maintains a moderate birefringence of 0.044@1064 nm and the real space atom cutting method indicates that the SiSe4 tetrahedra make the major contribution to its birefringence.

Distinctive modulation of optical anisotropy by halogens in α/ß-Cd-P-X (X = Cl, Br, and I).

Birefringent materials are widely applied as photoelectric functional field devices to modulate the polarization of lasers. The introduction of a halogen into the structure of crystals could balance the relationship between the band gap Eg and nonlinear optical (NLO) coefficient owing to their outstanding electronegativity and control the optical anisotropy. In this work, the optical properties of phosphohalides α/ß-Cd2P3X (X = Cl, Br, I) were studied. It was found that the birefringences of α/ß-Cd2P3Cl (0.23/0.24 @ 1064 nm) are unexpectedly 8 times larger than those of α/ß-Cd2P3I (0.04/0.03 @ 1064 nm). To find the optical property origins and explore the contributions of microscopic groups to the optical anisotropy and NLO responses in Cd-P-X (X = Cl, Br, I), the first-principles, real-space atom-cutting, and polarizability anisotropy analysis methods were used. This reveals that the electron distribution is susceptible to halogen electronegativity. Halogen atoms can modulate the polarization anisotropy of the active polyhedron and influence the birefringence significantly, owing to the synergistic effect of the anion size and strong covalent interactions between halogens and metal cations. This work clarifies the optical anisotropy origin mechanism and provides a general strategy for finding promising birefringent crystals in phosphohalide systems.

Synthesis, characterization and theoretical investigation of a new chalcohalide, Ba4GaS4F3.

A new fluorine-containing chalcohalide, Ba4GaS4F3, has been synthesized by conventional high-temperature solid-state reaction. The compound crystallizes in the centrosymmetric space group I41/a with a = b = 16.628 (5) Å, c = 17.139 (10) Å, Z = 16. Experimental and theoretical results confirm that Ba4GaS4F3 is a direct band gap compound with an experimental band gap of about 3.13 eV, and the band gap is mainly determined by the Ba-5p, F-2p and S-3p orbitals. What's more, different from the many newly discovered chalcohalides in the Ba3AM4Q (A = Ga, In; M = S, Se; Q = Cl, Br, I) family, Ba4GaS4F3 is the first reported compound in the Ba4AM4D3 (A = Ga, In; M = chalcogen; D = halogen) family. The results enrich the structural diversity of metal chalcohalides.

Syntheses, Structures and Properties of Alkali and Alkaline Earth Metal Diamond-Like Compounds Li2MgMSe4 (M = Ge, Sn).

Two new diamond-like (DL) chalcogenides, Li2MgGeSe4 and Li2MgSnSe4, have been successfully synthesized using a conventional high-temperature solid-state method. The two compounds crystallize in the non-centrosymmetric space group Pmn21 with a = 8.402 (14) Å, b = 7.181 (12) Å, c = 6.728 (11) Å, Z = 2 for Li2MgSnSe4, and a = 8.2961 (7) Å, b = 7.0069 (5) Å, c = 6.6116 (6) Å, Z = 2 for Li2MgGeSe4. The calculated results show that the second harmonic generation (SHG) coefficients of Li2MgSnSe4 (d33 = 12.19 pm/v) and Li2MgGeSe4 (d33 = -14.77 pm/v), mainly deriving from the [MSe4] (M = Ge, Sn) tetrahedral units, are close to the one in the benchmark AgGaS2 (d14 = 13.7 pm/V). The calculated band gaps for Li2MgSnSe4 and Li2MgGeSe4 are 2.42 and 2.44 eV, respectively. Moreover, the two compounds are the first series of alkali and alkaline-earth metal DL compounds in the I2-II-IV-VI4 family, enriching the structural diversity of DL compounds.