Inorganic Framework Research Articles

Fashioning Fluorous Organic Spacers for Tunable and Stable Layered Hybrid Perovskites

Two dimensional (2D) organic–inorganic hybrid perovskites have recently attracted enormous attention due to their higher environmental stability with respect to three-dimensional (3D) perovskites and larger structural tunability. The layered structure relaxes constraints on the dimensions of the organic cations that alternate the inorganic sheets, opening up a large choice on the organics, ultimately enabling the creation of tunable layered perovskites. Here, we report on a series of fluorous cations, varying in size and shape, as building blocks for a new family of fluorous 2D lead-iodide perovskites. These display a large tunability in the optical and dielectric properties depending on the structure of the fluorous cations. Importantly, despite the invariant inorganic framework, the 2D perovskite electronic structure is strongly affected by the cation size. The longer the cation, the smaller the 2D perovskite band gap and the exciton binding energy (reducing from 400 meV down to 130 meV). Such variation...

Structural Phase Transition and Switchable Dielectric Properties of a Unique Two-Dimensional Organic–Inorganic Hybrid Perovskite Compound [C6H11NH2CH3]4Pb3I10

The two-dimensional (2D) organic–inorganic hybrid perovskites with structural phase transition have been widely concerned for its diverse physical attributes. In the present work, an organic–inorganic hybrid perovskite compound with a 2D layered structure, (N-methylcyclohexylaminium)4Pb3I10 (1), has been synthesized. Interestingly, the inorganic framework of 1 adopts a unique 2D layer, in which the distorted skeletons of face-sharing octahedra are linked by four I atoms on terminals. Specific heat and differential scanning calorimetry (DSC) tests disclose that 1 experiences an invertible phase transition at 254 K with a thermal hysteresis of ∼11 K. In particular, the disorder–order dynamics of organic moieties and the deformation of inorganic layers account for its switchable dielectric responses along with dielectric anisotropic properties around 254 K. Besides, 1 exhibits a semiconducting feature with an optical band gap Eg = 2.48 eV. The electronic structure calculations show that the inorganic framework contributes to the band gap of 1. It is believed that our work would spur the exploration of novel organic–inorganic hybrid materials with multifunctionalities.

Enabling Stable Lithium Metal Anode via 3D Inorganic Skeleton with Superlithiophilic Interphase

AbstractThe lithium metal battery (LMB) is among the most sought‐after battery chemistries for high‐energy storage devices. However, LMBs usually undergo uncontrollable lithium deposition and severe side reactions, which significantly impede their practical applications. Herein, a stable Al2O3‐based inorganic framework with superlithiophilic lithium aluminum oxide (Li‐Al‐O) interphase is created via reacting Li with Al2O3 nanoparticles. The Al2O3‐based inorganic framework can serve as a stable Li “host,” reducing the volume expansion during cell cycling. Moreover, the strong interaction between Li‐Al‐O interphase and Li+ can redistribute Li+ and reduce the ion concentration gradient near surface protrusion, thus reducing uneven lithium electrodeposition. From galvanostatic measurements, symmetric cells with the 3D Al2O3‐hybrid electrode can operate under an ultrahigh current density of 8 mA cm−2 over 480 cycles. When used in full cells, it improves the capacity retention of Li/LiFePO4 from 78.4% to 93.6% after 200 cycles and enables long‐term operation of Li/Li4Ti5O12 for over 1200 cycles.

Hierarchical nanoporous γ-Al2O3 encapsulated quasi solid electrolyte with superior conductivity and high safety for lithium metal batteries

Dendrite growth and safety issues in a liquid electrolyte seriously hinder the development of Li metal batteries. Hierarchical nanoporous γ-Al2O3 is synthesized through a hydrothermal method, followed by sufficient encapsulation of a typical organic liquid electrolyte (1 M LiPF6 in EC:DMC). Thus obtained quasi solid electrolyte (QSE) displays combined advantages of the rigid inorganic framework (from solid γ-Al2O3) and high ionic conductivity (from liquid organic electrolyte). Specifically, the QSE affords a conductivity of 1.1 × 10−3 S cm−1 at room temperature and behaves a fine lithium ion transference number of 0.62. Inheriting the merits of solid framework, it also exhibits remarkable thermal/mechanical stabilities and a broad electrochemical window up to 5.0 V (vs. Li+/Li). The assembled LiFePO4 (LFP)/QSE/Li cell delivers a high specific capacity of 136.8 mAh g−1 after 50 cycles, with capacity retention of 96.5% at room temperature, which is mainly attributed to the high ionic conductivity and remarkably suppressed Li dendrite growth by the QSE. This work extends the application of hierarchical nanoporous structure and enables a safe, efficient operation of Li anode in next generation energy storage systems.

Dynamic Disorder Dominates Delocalization, Transport, and Recombination in Halide Perovskites

Summary We investigate the origins of exceptionally long charge-carrier lifetimes of halide perovskites by using temperature-dependent and time-resolved mid-infrared spectroscopy. We report direct observations of large polarons through their distinct mid-infrared electronic transitions and quantitatively correlate their formation with enhancement of electron-phonon coupling that quenches photoluminescence. The temperature-dependent study reveals a branching between free-carrier and large-polaron states in association with thermally induced dynamic disorder of the anharmonic inorganic framework, which is examined through local vibrational modes of the perovskite films. This dynamic disorder localizes charge carriers and enhances electron-phonon coupling, which both quenches photoluminescence and promotes large-polaron formation. Fortunately, such localization extends the charge recombination lifetime by nearly an order of magnitude. This work highlights the interplay between charge-carrier mobility and lifetime and suggests design rules about how cation and anion substitution can be used to tune the structural dynamics that underpin their relationship.

Palm Kernel Shell Activated Carbon as an Inorganic Framework for Shape-Stabilized Phase Change Material.

The preparation of activated carbon using palm kernel shells as the precursor (PKSAC) was successfully accomplished after the parametric optimization of the carbonization temperature, carbonization holding time, and the ratio of the activator (H3PO4) to the precursor. Optimization at 500 °C for 2 h of carbonization with 20% H3PO4 resulted in the highest surface area of the activated carbon (C20) of 1169 m2 g−1 and, with an average pore size of 27 Å. Subsequently, the preparation of shape-stabilized phase change material (SSPCM-C20) was done by the encapsulation of n-octadecane into the pores of the PKSAC, C20. The field emission scanning electron microscope images and the nitrogen gas adsorption-desorption isotherms show that n-octadecane was successfully encapsulated into the pores of C20. The resulting SSPCM-C20 nano-composite shows good thermal reliability which is chemically and thermally stable and can stand up to 500 melting and freezing cycles. This research work provided a new strategy for the preparation of SSPCM material for thermal energy storage application generated from oil palm waste.

Visible‐Light‐Driven Photocatalytic Oxidation of Organic Chlorides Using Air and an Inorganic‐Ligand Supported Nickel‐Catalyst Without Photosensitizers

AbstractEngineering photoredox‐triggered chemical transformation via visible light has been an emerging area in organic synthesis. However, most of the well‐established photocatalysts are based upon either transition metal complexes involved with noble metals and organic ligands or photosensitive organic dyes, the development of pure inorganic molecular photocatalysts that could provide better stability and durability is greatly retarded. Herein we discover that the Anderson polyoxometalate (POM) Na4[NiMo6O18(OH)6] (1), which consists of pure inorganic framework built from a central NiII core supported by six MoVIO6 inorganic scaffold/ligands, can be used as a powerful photocatalyst. Upon irradiation with visible light (>400 nm), the compound can catalyze, in high efficiency, a wide range of reactions, including the oxidative cross‐coupling reaction of chlorides with amines, as well as oxidation of chlorides using molecular oxygen, affording various imines, aldehydes, and ketones, respectively in high selectivity and good yields. Owing to the robust inorganic framework, this catalyst exhibits excellent stability during the catalysis and reusability with little loss of the catalytic activity, thus providing an alternative without use of complicated organic ligands and expensive noble metal‐based photosensitizers.

The influence of isothermal aging, surfactant and inorganic precursors concentrations on pore size and structural order of mesoporous bioactive glass

Ordered hexagonal mesoporous bioactive glasses (MBGs) are synthesized by an evaporation-induced self-assembly (EISA) method using tetraethylorthosilicate (TEOS), calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) and triethyl phosphate (TEP) as the silicon, calcium, phosphorous sources, respectively, and pluronic P123 as the structure directing agent. The influences of P123, TEOS, TEP, and Ca(NO3)2.4H2O on the structural order and pore size of MBGs at different environmental conditions are studied. The prepared MBGs are characterized by the small angle X-ray diffraction (SXRD), N2 adsorption-desorption isotherms, and transmission electron microscopy (TEM). The study revealed that polymerization degree of inorganic precursors should be low enough at the initial assembling stage of inorganic species with organic surfactants to form highly ordered mesoporous structure. Concentration of Ca(NO3)2 governs the formation of ordered mesostructure in MBGs by complexation of Ca2+ with the hydrophilic group of surfactant P123. Isothermal aging also plays an important role in the formation of highly ordered MBGs as it permits formation of rigid inorganic framework.

Effects of Surface Passivation on Trap States, Band Bending, and Photoinduced Charge Transfer in P3HT/TiO2 Hybrid Inverse Opals

We investigate the effect of a common TiO2 passivation reagent, TiCl4, on the photoinduced charge transfer of poly(3-hexylthiophene) (P3HT) to TiO2 in the inverse opal structure. Treating the inorganic oxide framework with TiCl4 leads to an increase in the size of the TiO2 nanoparticles, a thickening of the inverse opal framework, and a decrease in the trap-state photoluminescence. These changes lead to different energy alignments at the interface. In comparison to the unpassivated P3HT/TiO2 inverse opal, we measured a larger polaron yield, by as high as ninefold, and significantly shorter and more uniformly distributed polaron lifetimes in TiCl4-treated samples. We show that downward band bending in the polymer can be circumvented by tuning the trap states on the metal oxide using TiCl4, thereby eliminating the energetic barrier for photoelectron injection from the polymer to the metal oxide. The findings suggest a way to overcome a potential factor that has plagued the performance of metal oxide–polymer...

A novel -Pb-O-Pb-Cu-Cl- inorganic layer-based pillared-layer framework: Synthesis, crystal structure and fluorescent property

A novel pillared-layer coordination polymer containing -Pb-O-Pb-Cu-Cl- inorganic sheets, [PbCuCl(3.5-pydc)]n (1) (3.5-H2pydc = pyridine-3,5-dicarboxylic acid), was obtained through the hydrothermal method. In compound 1, two symmetry-related Pb centers are bridged into a Pb2O2 dimer by two symmetrically carboxyl oxygen atoms from 3,5-pydc2− anions, each Pb2O2 dimer links four equivalent units into a 2D puckered Pb-O-Pb layer. Two symmetry-related Cu ions are bridged into a Cu2Cl2 dimer by two chlorine ions. Thus the -Pb-O-Pb- layer and Cu2Cl2 dimers are joined into a novel 2D puckered -Pb-O-Pb-Cu-Cl- inorganic layer. The 2D -Pb-O-Pb-Cu-Cl- inorganic layers are further pillared to form a 3D network through 3,5-pydc2− anions. To the best of our knowledge, the pillared-layer framework based on -Pb-O-Pb-Cu-Cl- inorganic layers has never been reported previously. Compound 1 exhibits weak blue light emission with the maximum at 383 nm upon excitation at 260 nm.

An MOF-like Interpenetrated 2D Plus 2D to 3D Inorganic Grid Assembled by Linear Inorganic Pillars, Structures, and Properties in Supercapacitance.

Remarkable progresses regarding pure inorganic frameworks and metal-organic frameworks (MOF) have been made. However, pure inorganic frameworks with MOF-like grid structures are rarely reported due to the weakness of inorganic moiety as a long linear linker. We report herein a fascinating inorganic framework assembled by a [Ge4S10]4- cluster node and a linear [-Cu-MS4-Cu-] (M = Mo (1) and W (2)) inorganic pillar. Their network shows MOF-like orthogonal structure with two interpenetrated two-dimensional (2D) plus 2D to 3D framework and a 1D nano tunnel. Electrodes with crystalline sample of 1 and 2, inorganic sulfide framework, were prepared, and their quasi-capacitance behaviors were investigated. Electrochemical performances were evaluated by cyclic voltammetry and galvanostatic charge-discharge techniques in CsOH, KOH, NaOH, and LiOH electrolytes. The results revealed that the crystal materials exhibit moderate specific capacitance values that are comparable to those of porous sulfide materials.

Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability.

The chemical stabilities of hybrid perovskite materials demand further improvement toward long-term and large-scale photovoltaic applications. Herein, the enhanced chemical stability of CH3 NH3 PbI3 is reported by doping the divalent anion Se2- in the form of PbSe in precursor solutions to enhance the hydrogen-bonding-like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe-doped CH3 NH3 PbI3 films exhibited >140-fold stability improvement over pristine CH3 NH3 PbI3 films. As the PbSe-doped CH3 NH3 PbI3 films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI3 -based cell. As a bonus, the incorporated Se2- also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.

Single-crystalline layered metal-halide perovskite nanowires for ultrasensitive photodetectors

Metal-halide perovskites have long carrier diffusion lengths, low trap densities and high carrier mobilities, and are therefore of value in the development of photovoltaics and light-emitting diodes. However, the presence of thermally activated carriers in the materials leads to high noise levels, which limits their photodetection capabilities. Here, we show that ultrasensitive photodetectors can be created from single-crystalline nanowire arrays of layered metal-halide perovskites. A series of nanowires was fabricated in which layer-by-layer self-organization of insulating organic cations and conductive inorganic frameworks, along the nanowire length, creates high resistance in the interior of the crystals and high conductivity at the edges of the crystals. Using these structures, high-performance photodetection was achieved with responsivities exceeding 1.5 × 104 A W−1 and detectivities exceeding 7 × 1015 jones. Our state-of-the-art device performance originates from a combination of efficient free-carrier edge conduction and resistive hopping barriers in the layered perovskites. Photodetectors made from single-crystalline nanowire arrays of layered metal-halide perovskites exhibit detectivities of more than 7 × 1015 jones, due to a nanowire structure that combines high resistance in the interior of the crystals and high conductivity at the edges of the crystals.

First-Principles Calculations of the Rotational Motion and Hydrogen Bond Capability of Large Organic Cations in Hybrid Perovskites

The organic cation dynamics in organic–inorganic hybrid perovskites affect the unique physical properties of these materials. To date, the rotational dynamics of methylammonium (CH3NH3+) and formamidinium (CH(NH2)2+) have been studied both experimentally and from first-principles calculations. Recently, a novel hybrid perovskite with large organic cation guanidinium (C(NH2)3+, GA), which exhibited extraordinarily long carrier lifetimes, was reported. In order to analyze physical properties of GA, we examined the detailed rotational potential energy surfaces and rotational energy barriers of GA in cubic-phase GASnI3 and alternative perovskites using first-principles calculations. The analysis revealed that the principal rotations of GA involve six hydrogen bonds between the organic cation and the inorganic framework in the crystals. Our results suggest that GA can effectively passivate under-coordinated iodine ions using its high hydrogen bond capability, which is consistent with the experimental speculati...

Pressure-Induced Structural Evolution and Optical Properties of Metal-Halide Perovskite CsPbCl3

Metal-halide perovskites have emerged as the most promising semiconductor materials for advanced photovoltaic and optoelectronic applications. Herein, we comprehensively investigate the optical response and structural evolution of metal-halide perovskite CsPbCl3 (ABX3) upon compression. Band gap realized a pronounced narrowing under mild pressure followed by a sharp increase, which could be ascribed to Pb–Cl bond contraction and inorganic framework distortion, respectively. The transformation of the crystal structure is confirmed and analyzed through in situ high-pressure X-ray diffraction and Raman experiments, consistent with the evolution of optical properties. Combining with the first-principles calculations, we understand the electronic band structure changes and phase transition mechanism, which are ascribed to severe PbCl6 octahedral titling and twisting. Our results demonstrate that the high-pressure technique can be used as a practical tool to modify the optical properties of metal-halide perovsk...

Synthesis, physico-chemical studies and Hirshfeld surface analysis of a first 0-D Chlorozincophosphate, (H2N(CH2)4NH(CH2)2NH3Cl)ZnCl2(HPO4)

An original zero-dimensional chloro-substituted zincophosphate monomer, (H2N(CH2)4NH(CH2)2NH3Cl)Zn(HPO4)Cl2, was isolated by the reaction of zinc chloride (Zn2+, 2Cl−) with the amine, 1-(2-aminoethyl)piperazine, H3PO4 and HCl under ambient conditions. This phase crystallizes in the triclinic space group P-1 (No. 2) with the lattice parameters a = 8.834(2), b = 8.539(3), c = 11.163(2) A, α = 93.58(2)°, β = 108.62(2)°, γ = 62.96(2)°, V = 707.3(4) A3, Z = 2, R = 0.027 and Rw = 0.037. The tri-protonited organic cations are linked to the isolated chloride ions Cl− through N–H⋯Cl and C–H⋯Cl hydrogen bonds, forming corrugated cationic layers extending parallel to (a b) plane. The inorganic framework of the title compound consists of a network of ZnO3Cl and HPO4 tetrahedral units linked by their oxygen vertices, forming isolated 4-membered rings. These anionic monomers, (Zn2P2O8Cl4H2)4−, which are held by O–H⋯O hydrogen-bonding interactions, lie between the cationic layers to maximize the electrostatic interactions and are linked to (H2N(CH2)4NH(CH2)2NH3Cl)2+cations via N–H⋯O or N–H⋯Cl hydrogen bonds, forming a 3-D supra molecular structure. Hirshfeld surface analysis, Solid state NMR, Infrared spectroscopies and DTA/TGA analysis were also performed to characterize the title compound. Solid state31P and13C MAS NMR spectroscopy results were found to be in full agreement with the XRD results.

Syntheses, Crystal Structures and Properties of a Series of 3D Metal-Inorganic Frameworks Containing Pentazolate Anion.

Pentazolate anion (cyclo-N5- ), and/or N3- , NO3- were used as the ligands to obtain a series of nitrogen-rich energetic three-dimensional (3D) frameworks [Cu(N5 )(N3 )]n , [Ag(N5 )]n , [Ba(N5 )(NO3 )(H2 O)3 ]n , and [NaBa3 (N5 )6 (NO3 )(H2 O)3 ]n by self-assembly. These frameworks were characterized by single-crystal X-ray diffraction, SEM, IR and Raman spectroscopy, elemental analysis, and thermal analysis. All the frameworks exhibited regular supramolecular structures and excellent stabilities at room temperature which can be attributed to the strong coordination bonds between cyclo-N5- anions and metal ions. The successful stabilization of the cyclo-N5- in more 3D multi-ligand metal-N5- frameworks after Na-N5- frameworks has been demonstrated. This breakthrough offers new opportunities for the future of metal-pentazolate frameworks and polynitrogen chemistry.

Synthesis, structural characterisations, NMR spectroscopy, Hirshfeld surface analysis and electrochemical study of a new organic cyclohexaphosphate, (C6H7FN)4(Li)2(P6O18) (H2O)6

(C6H7FN)4(Li)2(P6O18) (H2O)6(I), a new organic cyclohexaphosphate, has been synthesized and grown at room temperature by an acid/base reaction between H6P6O18 and 2-fluoroaniline as an organic template. The crystal structure of (I) was solved by single crystal X-ray diffraction analysis and it was found that the material belongs to triclinic system with space group P-1 and refined R-factor of 0.0520. Adjacent P6O18 rings are connected via corner-sharing by LiO4 tetrahedra, generating anionic [Li2P6O18·H2O]4- layers parallel to the (a, b) plane. The 2-fluoro-anilinium cations are inserted in the interlayer space and interact with the inorganic framework through NH⋯O and OH⋯O hydrogen-bonding interactions. Additional stabilization is provided by strong NH⋯F and weak CH⋯O hydrogen bonds. Hirshfeld surface analysis reveals the nature of intermolecular contacts of the title compound and their enrichment ratio reveals if they are over-represented. The crystal packing is a combination of strong electrostatic attractive interactions and of weaker hydrophobic contacts. The title compound was further characterized by FT-IR and NMR spectroscopies. Crystal symmetry is confirmed by 31P magic angle spinning NMR and the vibrational absorption bands were identified by infrared spectroscopy. Electrical conductivity was studied using impedance spectroscopy and results showed that the conductivity at 150 °C was equal to 4.93 × 10−4 S cm−1. It is therefore concluded that (C6H7FN)4(Li)2(P6O18) (H2O)6 can be further used in lithium batteries.

Strain induced electronic structure variation in methyl-ammonium lead iodide perovskite

Methyl-ammonium lead iodide perovskite (CH3NH3PbI3) has drawn great attention due to its excellent photovoltaic properties. Because of its loosely compacted structure, the structural, electronic and optical properties of CH3NH3PbI3 are sensitive to external modulations. Strain effects on CH3NH3PbI3 are fully investigated by the first principles calculations. The results indicate that the inorganic framework deforms under compression or stretch and the embedded organic CH3NH3+ molecules rotate correspondingly. A band gap oscillation and a new structural phase in response to the external strain were observed for the first time. These phenomena are explained with the nonlinear structural deformation and phase transition under the external strains. The semi-quantitative relationship between the band gap variation and geometry change under the external strain is obtained. We found that the shift of valence band maximum under the external strain is mostly determined by the most stretched or compressed Pb-I bond of CH3NH3PbI3, and the shift of the conduction band minimum under the external strain is likely to be determined by the largest Pb-I-Pb bond angle in the system. These results are important for understanding of strain effects on semiconductors and guiding the experiments to improve the performance of the perovskite solar cells.

Organic Cathode for Aqueous Zn-Ion Batteries: Taming a Unique Phase Evolution toward Stable Electrochemical Cycling

Aqueous zinc ion batteries are highly attractive for large-scale storage applications because of their inherent safety, low cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn2+ inside solid inorganic frameworks. Here, we report on a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn2+ storage. It delivers a high capacity of ≥200 mAh g–1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of >200 Wh kg–1 at an unparalleled energy efficiency (∼95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-chloranil undergo a twisted rotation to accommodate Zn2+, thus restricting the volume change (−2.7%) during cycling. In-depth characterizations using operando X-ray diffraction, electron microscopy, and impedance analysis reveal a unique phase evolution, driven by a phase transfer mechanism occurring at the boundary of solid and liquid phase, which leads to unrestricted growth of discharged/charged phases. By confining the p-chloranil inside nanochannels of mesoporous carbon CMK-3, we can tame the phase evolution process, and thus stabilize the electrochemical cycling.