Three-dimensional Open-framework Structure Research Articles

Multi-metal substituted Fe-based Prussian blue as high-capacity cathode material for potassium ion batteries

Fe-based Prussian blue (FePB) has been widely studied as cathode materials of potassium ion batteries due to its three-dimensional open framework structure and large ion migration channels. In this study, the effect of the introduction of various metals (Co2+, Cu2+, Ni2+, Mn2+) on the rate and cycle properties of FePB was investigated. MnCoNiFePB cathode material shows better electrochemical performance, with the initial discharge capacity of 91.3 and 75.4 mAh/g (capacity retention is 56.7 % after 100 cycles) at 0.2C and 1C, respectively. These results inspire new ideas for the development and application of potassium ion battery electrode materials.

Polyaniline-modified amorphous tin-based Prussian blue analogue as cathodes for long-life aqueous zinc ion batteries

Prussian blue analogs (PBAs) have emerged in the field of aqueous zinc ion batteries (AZIBs) owing to their simple synthesis method and three-dimensional open framework structure. Although PBAs have high redox potentials, the unsatisfactory specific capacity and poor electrical conductivity limit their development to some extent. In this work, amorphous tin hexacyanoferrate (SnHCF) and polyaniline (PANI) were combined to form SnHCF/PANI composite. The synergistic effect of the amorphous structure of SnHCF and PANI with good conductivity makes the SnHCF/PANI electrode exhibit excellent redox activity and achieve rapid ion/electron transfer. When used as a cathode in AZIBs, the SnHCF/PANI provides a high specific capacity (136.8 mAh g−1 at 0.5 A g−1) and excellent cycling stability (a discharge specific capacity of 54.3 mAh g−1 after 2500 cycles at 2 A g−1). This work offers a new idea for the development of PBAs-based composites as cathode materials for AZIBs.

Dual-salt assisted synergistic synthesis of Prussian white cathode towards high-capacity and long cycle potassium ion battery

Prussian blue analogues (PBAs) are considered as superior cathode materials for potassium-ion batteries (PIBs) because of their three-dimensional open framework structure, high stability, and low cost. However, the intrinsic lattice defects and low potassium content typically results in poor rate and cycling performance, thus limited their practical applications. In this work, high-quality K1.64FeFe(CN)6 (PW-HQ) material with less crystalline water (6.21%) and high potassium content (1.64 mol−1) was successfully synthesized by a novel coprecipitation method with potassium citrate (K-CA) and potassium chloride (KCl) addition. Specifically, the electrode delivers a reversible capacity of 113.1 mA h g−1 at the current rate of 50 mA g−1 with ∼100% coulombic efficiency. Besides, the electrode retained 90% reversible capacity at 500 mA g−1 current density after 1000 cycles, indicating only 0.01% capacity decay per cycle. Moreover, we have revealed that the introduction of K-CA controlled the chelating rate of Fe(II) and the addition of KCl increased the K+ content, hence improving the capacity and stability of the as-prepared electrodes. Structural evolution and potassium storage mechanism were further investigated by detailed ex-situ X-ray diffraction and in-situ Raman measurements, which demonstrated reversible potassiation/depotassiation behavior and negligible volume change during the electrochemical process. In general, this work provides an efficient strategy to eliminate water contents in Prussian blue cathode and improve its electrochemical performance, which plays a key role in promoting the industrialization of potassium ion batteries.

Boosting sodium-storage behaviors of NASICON-type NaTi2(PO4)3 anode by synergistic modulations in both materials and electrolytes towards aqueous Na-ion batteries

NASICON-type NaTi2(PO4)3 (NTP) is one of the most competitive anode materials for aqueous sodium-ion batteries (ASIBs), thanks to its unique three-dimensional open framework structure, high ionic conductivity and good chemical stability. However, the low electrical conductivity of NTP and the oxygen reduction induced side reactions seriously affect its practical applications. To well address the above issues, the synergistic regulation strategy in electrode materials and electrolytes is motivatively put forward. The porous single-crystal NTP micro-sized framework coated with conductive carbon nano-layer (denoted as NTP@C) is designed with significantly improved electronic conductivity and structural stability. With further regulations in both the dissolved oxygen content and pH values of aqueous Na2SO4 electrolyte, the enhanced reversible capacities and cyclic stability especially at high rates are achieved by effectively alleviating side reactions. As a result, the fabricated NTP@C anode is optimized with a high-rate capability and remarkable long-duration electrochemical stability in the N2-purged aqueous Na2SO4 electrolyte with pH = 8.0. Furthermore, the assembled NTP@C//Na0.44MnO2 ASIBs exhibit high energy density of ∼40.0 Wh kg‒1 along with excellent cycling stability. More significantly, our work provides an insightful guideline for rational construction of other advanced aqueous rechargeable batteries.

Unlocking fast and highly reversible sodium storage in Fe-based mixed polyanion cathodes for low-cost and high-performance sodium-ion batteries

The iron-based polyanionic material Na3Fe2(PO4)P2O7is regarded as an excellent cathode due to its outstanding thermal stability and the three-dimensional (3D) open framework structure with facile sodium-ion transport.

Reducing atmosphere improves the conductivity of NaTi2(PO4)3/C material for hybrid aqueous rechargeable lithium-ion battery anode

Hybrid aqueous rechargeable lithium-ion batteries (HARLIBs) have lower cost and better safety performance than conventional lithium-ion batteries (organic electrolytes). The challenge faced by HARLIBs are the narrow selection of anode and cathode materials, and overcoming the problems of capacity decay of anode and cathode materials in aqueous electrolytes. NaTi2(PO4)3, which has a stable three-dimensional open framework structure, shows certain applicability in HARLIBs, but its inherent low electronic conductivity leads to poor utilization of active materials and inferior rate performance. In this article, we propose an experimental method that can improve the conductivity of NaTi2(PO4)3/C, and study the electrochemical performance of NaTi2(PO4)3/C aqueous half-cell and NaTi2(PO4)3/C||LiMn2O4 hybrid aqueous full cell. The results show that Ti3+/oxygen vacancies can endow NaTi2(PO4)3/C with higher conductivity and improve the specific capacity and rate capability (69 mAh·g−1, 7C). At 1C, the second discharge specific capacity is 98.46 mAh·g−1. After 100 cycles, the Rct was 2.92 × 10−2 Ω. The NaTi2(PO4)3/C//LiMn2O4 full cell can provide a discharge specific capacity of up to 101.07 mAh·g−1. The synthesized NaTi2(PO4)3/C material can be applied to the anode electrode of hybrid aqueous lithium-ion full cell.

Decoration of nickel hexacyanoferrate nanocubes onto reduced graphene oxide sheets as high-performance cathode material for rechargeable aqueous zinc-ion batteries

Prussian blue analogues (PBA) have attracted much attention in energy research due to their unique three-dimensional open framework structure, adjustable metal ions, and facile synthesis. However, the application of PBA as a cathode material for aqueous zinc-ion batteries (ZIBs) is restricted by its poor cycling performance and lower capacity. In this paper, we develop a new PBA-based hybrid cathode material for aqueous ZIBs by loading uniform nickel hexacyanoferrate (NiHCF) nanocubes onto reduced graphene oxide (RGO) sheets. In the NiHCF/RGO hybrid, NiHCF nanoparticles are well anchored on the RGO layers, forming a conductive network. The strong synergy between NiHCF and highly conductive RGO effectively increases the specific surface area, accelerates the electron and ion transport, and inhibits the structural collapse of the NiHCF/RGO electrode during the Zn2+ insertion/extraction process. Benefiting from the above advantages, the NiHCF/RGO hybrid exhibits a remarkable reversible capacity of 94.5 mAh g−1 at a current density of 5 mA g−1, excellent rate performance of 50.1 mAh g−1 at 200 mA g−1, and enhanced cycling stability with a capacity retention of 80.3% after 1000 cycles at 200 mA g−1. This work provides a simple and effective way to improve the electrochemical performance of PBA-based cathodes for aqueous ZIBs application.

First chiral fluorinated lead vanadate selenite Pb2(V2O4F)(VO2)(SeO3)3 with five asymmetric motifs and large optical properties.

The first fluorinated lead vanadate selenite Pb2(V2O4F)(VO2)(SeO3)3 (PVOFS) was successfully synthesized via a mild hydrothermal method. This compound crystallizes in the chiral space group P212121 of the orthorhombic system and it is the first noncentrosymmetric structure in the PbII-VV-SeIV-O-F system. PVOFS is composed of five kinds of second-order Jahn-Teller susceptible asymmetric motifs, including three distinct types of vanadium-centered polyhedral units ([VO5F], [VO6] and [VO5]), [SeO3] pyramids and Pb2+ cations. It features a unique three-dimensional open framework structure displaying three types of tunnels (10-, 8- and 7-membered rings), which enriches the structural diversity for fluorinated vanadate selenite systems. Optical property studies revealed that PVOFS shows a second-harmonic generation response of 0.3 times that of the commercial KH2PO4 with phase matching behavior, a wide transparent region covering IR windows, an optical band gap of 2.35 eV, a high laser damage threshold of 61 times that of AgGaS2, and a large birefringence of 0.105 at 1064 nm. Theoretical calculations have been performed to clarify the correlation between the molecular structure and the optical properties of PVOFS.

Effect of Electrolyte Anion on Electrochemical Behavior of Nickel Hexacyanoferrate Electrode in Aqueous Sodium-Ion Batteries

Nickel hexacyanoferrate (NiHCF) has a three-dimensional open framework structure, excellent long-cycling stability and rate performance as a cathode for aqueous sodium-ion batteries. However, the specific capacity of NiHCF is lower than that of present cathodes for aqueous batteries. A sodium-ion electrolyte was explored to achieve optimum capacity with NiHCF. Powder-type NiHCF was fabricated by coprecipitation with the atomic composition K0.065Ni1.44Fe(CN)6·4.4H2O. The presence of Fe vacancies in the atomic composition is attributable to the inclusion of coordinating and zeolitic water during coprecipitation. Two sodium-ion electrolytes, 1 M Na2SO4 and 1 M NaNO3, were employed to analyze the electrochemical behavior of the NiHCF electrode. Identical redox potentials to 0.58 V (vs. NHE) were measured in both electrolytes. However, a lower overpotential was observed in NaNO3 compared to Na2SO4 as a result of the smaller interfacial charge transfer resistance. The lower charge transfer resistance in the NaNO3 solution produced a higher specific capacity of 57 mAh g<sup>-1</sup> (1 C-rate) and the superior capacity retention of 46.6% at 20 C-rate. The anion in the aqueous electrolyte changed the charge transfer resistance at the electrode/electrolyte interface, confirming the electrolyte anion has a crucial effect on the charge capacity and rate performance of NiHCF.

Porous Na3V2(PO4)3/C as cathode material for high-rate sodium-ion batteries by sacrificed template method

NASICON-type Na3V2(PO4)3 with a three-dimensional open framework structure has attracted wide attention, and it is regarded as one of the most promising cathode material for sodium-ion batteries. However, the low electronic conductivity restricts its charge–discharge capacity and electrochemical performance. With the purpose to solve this problem, polystyrene microspheres are applied in the preparation of cathode materials for sodium-ion batteries. Particular porous-structured Na3V2(PO4)3 composing of interlaced nanosheets is obtained samples by a simple hydrothermal-assisted sol–gel method via a self-sacrificed template (polystyrene microsphere). As expected, the as-prepared porous sample delivers a reversible capacity of 109.2 mAh g−1 at 0.2 C, an excellent rate performance (89.6 mAh g−1 at 50 C) and superior cyclic stability (retention of 94% over 500 cycles at 50 C). The outstanding rate and cyclic performance are attributed to its unique porous structure which is conducive to improve electron conductivity and facilitate the diffusion of sodium ions.

Improving Potassium-Ion Batteries by Optimizing the Composition of Prussian Blue Cathode

Prussian blue and its analogues are considered as superior cathode materials for nonaqueous potassium-ion batteries because of their three-dimensional open framework structure, high stability, and ...

Organically templated metal sulfate-oxalates: Solvent-free synthesis, crystal structure, and proton conduction

Two new metal sulfate-oxalates, namely, (H4bapp)0.5·VO(SO4)(C2O4) (SCU-11) and H2depa⋅Mn2(SO4)(C2O4)2(H2O)⋅H2O (SCU-13), were prepared under solvent-free conditions, where bapp = 1,4-bis(3-aminopropyl)piperazine and depa = 3-(diethylamino)propylamine. SCU-11 has a chainlike structure containing pendant SO4 groups. SCU-13 has a three-dimensional open-framework structure with chainlike manganese oxalate chains assembled by SO4 groups. Notably, SCU-11 shows excellent water stability and a high proton conductivity of 1.2 × 10−3 S cm−1 at 25 °C under 98% relative humidity. The magnetic susceptibility data for the two compounds were also reported.

(Keynote) Polyanionic Compounds for K-Ion Batteries

We reported the high working voltage of K-ion battery (KIB) comparable to Li-ion and higher than Na-ion thanks to the standard potential of potassium is lower than those of lithium and sodium in non-aqueous electrolyte [1,2]. In 2015, our group reported graphite negative electrode delivering 250 mAh g-1 or higher with excellent reversibility [1]. Furthermore, a Prussian blue analogue (PBA) of K2Mn[Fe(CN)6] demonstrated highly reversible potassium insertion/extraction and 4 V operation, realizing a 4 V-class K2Mn[Fe(CN)6]/graphite full cell [3]. The previous studies revealed that a three-dimensional open framework structure of PBAs is suitable for insertion/extraction of large K+ ion. Addition to the PBAs, polyanionic compounds are potential positive electrode materials for KIBs due to their open framework structure and inductive effect. In this talk, our recent studies on potassium insertion into various polyanionic compounds, such as heterosite FePO4, KFePO4, KMnPO4, K2FeP2O7, K2MnP2O7, KVPO4F, KVOPO4, monoclinic KFeSO4F, and orthorhombic KFeSO4F (o-KFeSO4F) [4,5], will be presented to give a perspective of potassium insertion material design. Because K+ ion is too large to occupy the octahedral site in heterosite FePO4 prepared from olivine-type LiFePO4, the crystallinity of heterosite FePO4 significantly decreases after potassium insertion. On the other hand, KVPO4F, KVOPO4, and o-KFeSO4F possess the KTiOPO4-type structure providing large channels to diffuse K+ ion and show the reversible potassium insertion/extraction properties and excellent rate performance. These results indicate that the crystal structure plays a key factor for reversible potassium insertion and rate performance. Moreover, the average discharge voltage of KVPO4F and KVOPO4 is as high as 4 V in a K half-cell. That of o-KFeSO4F is 3.6 V, which is notably high redox potential of Fe2+/Fe3+ due to the strong inductive effect of SO4 2- and F- on the Fe2+/3+ couple. The cycling stability of these high-voltage electrode materials is highly improved by using highly concentrated potassium salt solutions [6]. From these results, we will present our future insight into electrochemical potassium insertion chemistry for high voltage battery applications.

A New 3-D Open-Framework Zinc Borovanadate with Catalytic Potentials in α-Phenethyl Alcohol Oxidation.

A novel 3-D open-framework zinc borovanadate [Zn6(en)3][(VIVO)6(VVO)6O6(B18O36(OH)6)·(H2O)]2·14H2O (1, en = ethylenediamine) was hydrothermally obtained and structurally characterized. The framework was built from [V12B18O54(OH)6(H2O)]10− polyanion clusters bridged by Zn(en) complex fragments. The compound not only possessed a three-dimensional open-framework structure with unique plane-shaped channels, but also exhibited excellent catalytic activities for the oxidation of α-phenethyl alcohol.

Structural Insights into Borates with an Anion-Templated Open-Framework Configuration: Asymmetric K2 BaB16 O26 versus Centrosymmetric K3 CsB20 O32 and Na2 M2 NB18 O30 (M=Rb, Cs; N=Ba, Pb).

Five new mixed-metal borate crystals, namely, K2 BaB16 O26 , K3 CsB20 O32 , Na2 Cs2 BaB18 O30 , Na2 Rb2 PbB18 O30 , and Na2 Cs2 PbB18 O30 , have been synthesized by the high-temperature solution method. These structures were characterized by single-crystal X-ray diffraction and their B-O configurations are shown to feature complicated three-dimensional (3D) open-framework structures incorporating different types of channels. For all five compounds, the frameworks can be reduced to four-connected (4-c) uninodal nets with sra-, dia- and nbo-type topologies by assigning the [B5 O10 ]5- and [B3 O7 ]5- clusters as basic nodes. First-principles calculations have shown that the multiple cations in mixed-metal borates influence the ground-state electronic structures and associated optical absorptions. In addition, the crystal structures, thermal stabilities, and IR spectra of the title compounds have also been performed.

Porous Uranyl Borophosphates with Unique Three-Dimensional Open-Framework Structures.

Two novel alkali-metal uranyl borophosphates have been prepared and characterized for the first time, namely, K5(UO2)2[B2P3O12(OH)]2(OH)(H2O)2 and K2(UO2)12[B(H2PO4)4](PO4)8(OH)(H2O)6 denoted as KUPB1 and KUPB2, respectively. KUPB1 was obtained hydrothermally at 220 °C and crystallizes in a monoclinic structure in the chiral space group P21. The unit cell parameters of KUPB1 are a = 6.7623(2) Å, b = 19.5584(7) Å, c = 11.0110(4) Å, α = γ = 90°, β = 95.579(3)°, and V = 1449.42(8) Å3. It features a unique three-dimensional (3D) open-framework structure, composed of two corner-sharing linked one-dimensional (1D) anionic borophosphates (BP), [B2P3O13]5-, along the a axis and uranyl phosphate (UP), [(UO2)(PO4)3]7-, chains along the c axis, further bridged by PO4 tetrahedra. Multi-intersectional channels can be observed within the structure, in which the largest 11-ring (11-R) tunnel size is ∼7.0 Å × 8.8 Å. Its simplified framework can be described as a new 4-nodal net topological type with a point symbol of {4.84.10}{42.6}2{43.62.83.102}{82.10}. By modification of the synthetic conditions of KUPB1 through an increase in the amount of H3BO3 as flux 4-fold and a reduction of water as the reaction medium, the novel compound KUPB2 is generated. The unit cell parameters of KUPB2 are a = b = 21.8747(3) Å, c = 7.0652(2) Å, α = β = γ = 90°, and V = 3380.72(12) Å3. KUPB2 crystallizes in a tetragonal structure in the polar space group I4̅2m, and its structure is based on a highly complex 3D framework, {(UO2)12[B(PO4)4](PO4)8}9-, in which 1D 8-R UP [(UO2)(PO4)]- tubes can be observed along the c axis. The [(UO2)(PO4)]- tubes consist of three uranyl chains along the c axis, which are linked alternately by [PO4]3- tetrahedra. Those isolated 1D [(UO2)(PO4)]- tubes are further bridged through [(UO2)4B(PO4)4]- clusters, forming an exceptional 3D open-framework structure. Its simplified cation network is a new 5-nodal net topological type such as {32.43.5.62.7.8}8{34.45.54.62}8{4.62.83}4{42.6}4{44.62}. Their facile hydrothermal synthetic routes, porous structure topology, thermal stability, and Raman spectroscopy properties are reported and discussed.

Solvent-free synthesis of open-framework manganese phosphate-oxalates with 4-connected topologies

Two manganese phosphate-oxalates, namely, H2aep·Mn2(H2PO4)2(C2O4)2·H2O (1) and H2epip·Mn2(H2PO4)2(C2O4)2 (2), were prepared under solvent-free conditions, where aep=1-(2-aminoethyl)piperazine and epip=1-ethylpiperzaine. The two hybrid solids have three-dimensional open-framework structures with 12-, and 16-ring channels, respectively. Topological analysis reveals that they have 4-connected lon and mog nets. The magnetic properties of the two compounds were also investigated.

Hydrothermal synthesis of two supramolecular inorganic–organic hybrid phosphomolybdates based on Ni(ii) and Co(ii) ions: structural diversity and heterogeneous catalytic activities

Two new compounds (NHEPH2)5[NiII(P4Mo6O31)2]·6H2O (1) and {(NHEPH2)2[CoII(H2O)6]}[P2Mo5O23]·2H2O (2) exhibited heterogeneous styrene oxidation by H2O2 under mild conditions.

An investigation of polyhedral deformation in two mixed-metal diarsenates: SrZnAs₂O₇ and BaCuAs₂O₇.

Two isostructural diarsenates, SrZnAs2O7 (strontium zinc diarsenate), (I), and BaCuAs2O7 [barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. The three-dimensional open-framework crystal structure consists of corner-sharing M2O5 (M2 = Zn or Cu) square pyramids and diarsenate (As2O7) groups. Each As2O7 group shares its five corners with five different M2O5 square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine-coordinated M1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of the M1O9, M2O5 and As2O7 groups of known isostructural diarsenates, adopting the general formula M1(II)M2(II)As2O7 (M1(II) = Sr, Ba, Pb; M2(II) = Mg, Co, Cu, Zn) and crystallizing in the space group P2₁/n, are presented and discussed.

Solvent-free synthesis of new metal phosphites with double-layered, pillared-layered, and framework structures

Three new metal phosphites, formulated as (H3O)2·Mn2(HPO3)3 (1), Co(bpy) (H2O) (HPO3) (2), and H2tmpda·Zn3(HPO3)4 (3), have been synthesized under solvent-free conditions, where bpy = 4,4′-bipyridine, and tmpda = N,N,N′,N′-tetramethyl-1,3-propanediamine. Compound 1 has a double-layered structure with a thickness of 5.68 Å. Compound 2 has an inorganic-organic hybrid framework with cobalt phosphite layers pillared by bpy ligands. Compound 3 has a three-dimensional open-framework structure containing 8-ring channels. The temperature dependence of the magnetic susceptibility of compounds 1 and 2 were also investigated.