Phase Conversion Research Articles

Multi-heterostructured MXene/NiS2/Co3S4 with S-Vacancies to Promote Polysulfide Conversion in Lithium-Sulfur Batteries.

The severe shuttle effect of polysulfides (LiPSs) and the slow liquid-solid phase conversion are the main obstacles hindering the practical application of lithium-sulfur (Li-S) batteries. Separator modification with a high-activity catalyst can boost LiPSs conversion and suppress their shuttle effect. In this work, multi-heterostructured MXene/NiS2/Co3S4 with rich S-vacancies was constructed facilely with a hydrothermal and high-temperature annealing strategy for separator modification. The MXene sheet not only provides a physical barrier but also ensures a high conductivity and adsorption capacity of the catalyst; the dual active centers of NiS2 and Co3S4 catalyze LiPSs conversion. In addition, the vacancies and heterostructures can modulate the electronic structure of the catalyst, improve its intrinsic activity, and reduce the polysulfides reaction barrier, thus facilitating ion/electron transport and inhibiting the shuttle effect. Benefiting from these advantages, the Li-S battery with MXene/NiS2/Co3S4 modified separator exhibits exciting discharge capacities (1495.4 mAh g-1 at 0.1C and 549.0 mAh g-1 at 6C) and an excellent ultra-long cycle life (average capacity decay rate of 0.026% for 2000 cycles at 2C); at a high sulfur loading of 10.0 mg cm-2, the battery operates for nearly 80 cycles at 0.2C, giving a capacity retention rate of 75.76%. This work provides a high-activity catalyst for Li-S batteries.

Schottky Junctions with Bi@Bi2MoO6 Core-Shell Photocatalysts toward High-Efficiency Solar N2-to-Ammonnia Conversion in Aqueous Phase.

The photocatalytic nitrogen reduction reaction (NRR) in aqueous solution is a green and sustainable strategy for ammonia production. Nonetheless, the efficiency of the process still has a wide gap compared to that of the Haber-Bosch one due to the difficulty of N2 activation and the quick recombination of photo-generated carriers. Herein, a core-shell Bi@Bi2MoO6 microsphere through constructing Schottky junctions has been explored as a robust photocatalyst toward N2 reduction to NH3. Metal Bi self-reduced onto Bi2MoO6 not only spurs the photo-generated electron and hole separation owing to the Schottky junction at the interface of Bi and Bi2MoO6 but also promotes N2 adsorption and activation at Bi active sites synchronously. As a result, the yield of the photocatalytic N2-to-ammonia conversion reaches up to 173.40 μmol g-1 on core-shell Bi@Bi2MoO6 photocatalysts, as much as two times of that of bare Bi2MoO6. This work provides a new design for the decarbonization of the nitrogen reduction reaction by the utilization of renewable energy sources.

Re-usable Cd0.9Zn0.1S-ZnO@C/PVDF piezo-photocatalytic film with exceptional hydrogen evolution capability triggered by the synergetic advantages of piezoelectricity and S-Scheme heterojunction

Piezoelectric materials have advantages of fine-tuning photocatalytic performance through harvesting mechanical energy and open a new avenue in facilitating green catalytic reaction. Herein, polyvinylidene fluoride (PVDF), a flexible piezoelectric material, was introduced to synthesize a novel Cd0.9Zn0.1S-ZnO@C/PVDF (CZS-ZO@C/PVDF) piezo-photocatalytic film by spin coating and immersion phase conversion method. Benefiting from the piezoelectricity of PVDF and the internal electric field (IEF) of CZS-ZO@C Step-scheme (S-Scheme) heterojunction, CZS-ZO@C/PVDF was able to induce a hydrogen generation rate of 34.9 mmol g−1 h−1 activated by ultrasound and visible light (U-L), which is ∼17.5 times of Cd0.9Zn0.1S/PVDF (CZS/PVDF) and ∼7.4 times of the photocatalysis rate activated by visible light only (L). Piezoelectric measurements and COMSOL simulation illustrated the excellent piezoelectricity of CZS-ZO@C/PVDF film, which exhibits a piezoelectric coefficient (d33) of 9.9 pm V−1 and a piezoelectric potential of 874 mV (under 0.5 MPa). The reaction mechanism for the exceptional piezo-photocatalytic performance was finally disclosed through density functional theory (DFT) calculation and electrochemical tests. This study enriches the application scope of piezoelectric materials in sustainable energy catalysis and provides a new direction to develop efficient piezoelectric photocatalysts.

Highly selective granulation adsorbents for lithium recovery from gas field brine: Selectivity, kinetics and mechanism

Polyvinyl chloride (PVC)-based granulated adsorbents with high mechanical stability have proven effective for extracting lithium from salt lake brine on a commercial scale. However, granular materials with high adsorption selectivity for Na+/Li+ separation and long service life still remain a great challenge. Here, we prepared granulated spherical adsorbents by a phase conversion method using PVC as a binder; PEG, PMMA, PAN, and PAA as hydrophilic co-binders; and Li1.33Mn1.67O4 (LMO) as a powder adsorbent. Among these materials, P-PAA exhibited excellent hydrophilicity and excellent binder compatibility, facilitating the dispersion of LMO powders and ensuring high adsorption. Moreover, the mechanism of action of the PVC/PAA binders was first explored via experiments and simulations, which revealed that Li+ migration was promoted and occurred primarily on LMO rather than on binders, so nonselective adsorption decreased. Therefore, P-PAA demonstrated exceptional Li+ adsorption capacity (12.9 mg/g) and selectivity for Li+ (distribution factor of 1391.3 mL/g) over other coexisting cations and a separation factor of αNaLi= 718, which are greater than those of other adsorbents reported in the literature. Furthermore, the unique structure of P-PAA, which was obtained by interconnecting larger core pores (5–10 μm) and abundant smaller pores (0.5–1 μm), accelerated the water/ion transfer kinetics without causing powder leakage. Hence, the lifespan of these materials has been extended, as salt crystals or internal cracks did not form during long-term cyclic use, unlike in the case of other granules. All of the above factors made P-PAA effectively recover Li+ from Puguang gas brine, which contains a high sodium salt content and organic pollutants, with an efficiency of 98.4 %. All these properties demonstrate that P-PAA could be used in an appealing and competitive manner for industrial processes.

Excess antimony induced 12R Ba4Sb0.85Mn3.15O12 phase and Mn3O4 exsolution from 10H Ba5Sb0.7Mn4.3O15: Crystal structure and magnetic properties

Hexagonal perovskite manganite has attracted much attention due to its rich structural chemistry and magnetic properties. The transformation between BaMxMn1−xO3 polymorphs can be caused by the change in substitution level or oxygen vacancies. In this study, we find a new polymorph change from 10H Ba5Sb0.7Mn4.3O15 (P63/mmc) to 12R Ba4Sb0.85Mn3.15O12 (R3‾m) via a ‘topochemical’ reaction with excess Sb2O3. The 10H Ba5Sb0.7Mn4.3O15 structure contains BaO3 layers in a (cchhh)2 sequence and face-shared MnO6 tetramers (Mn4 clusters), while the 12R Ba4Sb0.85Mn3.15O12 structure consists of BaO3 layers in a (cchh)3 stacking and face-shared MnO6 trimers (Mn3 clusters). The 10H → 12R phase conversion accompanies the exsolution of the Mn3O4 phase in trace amounts. For both 10H Ba5Sb0.71Mn4.29O15 and 12R Ba4Sb0.85Mn3.15O12, the Mn3+ cation on the corner-shared octahedra at M1 sites mediated competing ferromagnetic and antiferromagnetic exchanges between the magnetic Mn3 and Mn4 clusters, leading to spin-freezing transition at TF ≈ 11–15 K. The 10H → 12R phase change leads to an abrupt change of 2 K saturation moment from Ms ≈ 0.1 μB of 10H Ba5Sb0.71Mn4.29O15 to Ms ≈ 1.75 μB of 12R Ba4Sb0.85Mn3.15O12.

Gas permeable membrane electrode assembly with in situ utilization of authigenic acid and base for transmembrane electro-chemisorption to enhance ammonia recovery from wastewater

Ammonia recovery from wastewater is of great significance for aquatic ecology safety, human health and carbon emissions reduction. Electrochemical methods have gained increasing attention since the authigenic base and acid of electrochemical systems can be used as stripper and absorbent for transmembrane chemisorption of ammonia, respectively. However, the separation of electrodes and gas permeable membrane (GPM) significantly restricts the ammonia transfer-transformation process and the authigenic acid-base utilization. To break the restrictions, this study developed a gas permeable membrane electrode assembly (GPMEA), which innovatively integrated anode and cathode on each side of GPM through easy phase inversion of polyvinylidene fluoride binder, respectively. With the GPMEA assembled in a stacked transmembrane electro-chemisorption (sTMECS) system, in situ utilization of authigenic acid and base for transmembrane electro-chemisorption of ammonia was achieved to enhance the ammonia recovery from wastewater. At current density of 60 A/m2, the transmembrane ammonia flux of the GPMEA was 693.0 ± 15.0 g N/(m2·d), which was 86 % and 28 % higher than those of separate GPM and membrane cathode, respectively. The specific energy consumption of the GPMEA was 9.7∼16.1 kWh/kg N, which were about 50 % and 25 % lower than that of separate GPM and membrane cathode, respectively. Moreover, the application of GPMEA in the ammonia recovery from wastewater is easy to scale up in the sTMECS system. Accordingly, with the features of excellent performance, energy saving and easy scale-up, the GPMEA showed good prospects in electrochemical ammonia recovery from wastewater.

A facile route to synthesize β‐Ga2O3 nanoparticles from γ‐polymorph through a rapid microwave route and their optical properties

AbstractDue to the wide bandgap, monoclinic structure and thermodynamic stability, β‐polymorph form of Ga2O3 nanomaterials is well‐received for various applications. However, as the γ‐Ga2O3 is difficult to synthesize, less attention has been paid towards it and its conversion to β‐polymorph. This paper reports the single‐step synthesis of γ‐Ga2O3 using a microwave‐assisted procedure. In this regard, γ‐Ga2O3 powders are synthesized in minutes using benzyl alcohol as the solvent using gallium acetylacetone as the precursor. The XRD of the as‐prepared powders indicates the formation of the γ‐Ga2O3 phase, the very broad peaks indicative of the small crystallite size as confirmed by TEM. The γ‐Ga2O3 powders were annealed at different temperatures and the complete phase conversion of γ‐Ga2O3 phase to β‐Ga2O3 phase happens at 700 °C. The TEM analysis shows the crystallite size to be ≈10 nm for the annealed β‐Ga2O3 phase. The as‐prepared nanopowders show very weak luminescence under excitation and in contrast, a blue‐green emission is observed in case of annealed powders. This confirms the presented strategy as having the potential to use β‐Ga2O3 nanopowders for different optoelectronic applications.

Enhancing piezoelectric properties of PVDF-HFP composite nanofibers with cellulose nanocrystals

With the increasing interest in flexible self-powering energy devices, piezoelectric polymers such as poly(vinylidene fluoride) (PVDF), PVDF-trifluoroethylene (PVDF-TrFE and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) have garnered substantial research attention. Among these, PVDF-HFP has demonstrated immense research potential in harvesting mechanical energy and converting it to electric energy. It is also particularly attractive due to its low cost compared to some other PVDF co-polymers. In this study, PVDF-HFP nanofibers were produced by electrospinning with cellulose nanocrystal (CNC) employed as a filler to improve their piezoelectric performance. Smooth and bead-free fibers were obtained with up to 1 wt% of CNC in the solution. The inclusion of CNC increased the uniformity of fiber diameter and improved thermal stability. Higher CNC concentration (2–3 wt%) engendered agglomeration and adversely impacted the conversion of non-polar phase to electroactive phase for PVDF-HFP molecules. At the optimal CNC concentration of 1 wt%, the voltage and current sensitivities for 1 cm2 samples were obtained as 0.146±0.048 mV/mN and 0.009±0.003 nA/mN, respectively. The open-circuit voltage output of 2.69±1.11 V was achieved under an average impact force of 40 N, and this increased with increased magnitude and frequency of the applied force. The mechanical properties of composite nanofibers maximized at 0.5 wt% CNC with tensile strength of 37.85±4.35 MPa, elastic modulus of 124.96±42.17 MPa, and strain at failure of 82.32±14.84 %. The improved piezoelectric and mechanical properties of the CNC-aided electrospun PVDF-HFP fibers will open new pathways for flexible energy harvesting systems.

Interfacial Enhancement and Composite Manufacturing of Continuous Carbon-Fiber-Reinforced PA6T Composites via PrePA6T Ultrafine Powder.

Semi-aromatic poly (hexamethylene terephthalamide) (PA6T) oligomer (prePA6T) ultrafine powder, with a diameter of <5 μm, was prepared as an emulsion sizing agent to improve the impregnation performance of CF/PA6T composites. The prePA6T hyperfine powder was acquired via the dissolution and precipitation "phase conversion" method, and the prePA6T emulsion sizing agent was acquired to continuously coat the CF bundle. The sized CF unidirectional tape was knitted into a fabric using the plain weave method, while the CF/PA6T laminated composites were obtained by laminating the plain weave fabrics with PA6T films. The interfacial shear strength (IFSS), tensile strength (TS), and interlaminar shear strength (ILSS) of prePA6T-modified CF/PA6T composites improved by 54.9%, 125.3%, and 120.9%, respectively. Compared with the commercial polyamide sizing agent product PA845H, the prePA6T sizing agent showed better interfacial properties at elevated temperatures, especially no TS loss at 75 °C. The SEM observations also indicated that the prePA6T emulsion has an excellent impregnation effect on CF, and the fracture mechanism shifted from adhesive failure mode to cohesive failure mode. In summary, a facile, heat-resistant, undamaged-to-fiber environmental coating process is proposed to continuously manufacture high-performance thermoplastic composites, which is quite promising in mass production.

Mid-Infrared, Optically Active Black Phosphorus Thin Films on Centimeter Scale.

Black phosphorus (BP) is a narrow bandgap (∼0.3 eV) semiconductor with a great potential for optoelectronic devices in the mid-infrared wavelength. However, it has been challenging to achieve a high-quality scalable BP thin film. Here we present the successful synthesis of optically active BP films on a centimeter scale. We utilize the pulsed laser deposition of amorphous red phosphorus, another allotrope of phosphorus, followed by a high-pressure treatment at ∼8 GPa to induce a phase conversion into BP crystals. The crystalline quality was improved through thermal annealing, resulting in the observation of photoluminescence emission at mid-infrared wavelengths. We demonstrate high-pressure conversion on a centimeter scale with a continuous film with a thickness of ∼18 nm using a flat-belt-type high-pressure apparatus. This synthesis procedure presents a promising route to obtain optical-quality BP films, enabling the exploration of integrated optoelectronic device applications such as light-emitting devices and mid-infrared cameras on a chip scale.

Removal of rubidium from brine by an integrated film of sulfonated polysulfone/graphene/potassium copper ferricyanide

A novel integrated film of sulfonated polysulfone/graphene/potassium copper ferricyanide (KCuFC/SPSG) was used for selectively extracting rubidium ion (Rb+) from brine. To form KCuFC/SPSG, the precursor film of sulfonated polysulfone/graphene (SPSG) was synthesized by phase conversion process, which was alternately immersed in 0.1 mol·L–1 CuSO4/K4[Fe(CN)6] by in-situ adsorption coupled co-precipitation method. Various data such as nuclear magnetic resonance spectrometer, Fourier transform infrared spectroscope, X-ray photoelectron spectroscope, X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy all verified that abundant KCuFC were uniformly located on the film. The resulting KCuFC/SPSG was used in film separation system. As the solution was fed into the system, the Rb+ could be selectively adsorption by KCuFC/SPSG. After the saturation adsorption, 0.5 mol·L–1 NH4Cl/HCl was fed into the film cell, Rb+ could be quickly desorbed by ion-exchange between Rb+ and NH4+ in the lattice of KCuFC. The purpose of separating and recovering Rb+ from the brine can be achieved after the repeated operation. The effects of pH, adsorption time and interferential ions on the adsorption capacity of Rb+ were investigated by batch experiments. The adsorption behavior fits the pseudo-second order kinetic process, while KCuFC has a higher adsorption capacity (Langmuir maximum sorption 165.4 mg∙g–1). In addition, KCuFC/SPSG shows excellent selectivity for Rb+ even in complex brine systems. KCuFC/SPSG could maintain 93.5% extraction efficiency after five adsorption/desorption cycles.

Evolution of α-V2O5 into electrochemically transformed NaV3O8 structure: Structural changes and supercapacitor application

Nowadays, cost-effective and environmentally friendly supercapacitors (SCs) with high energy and power densities are gaining significant research attention since they could broaden the application of capacitors. The present study demonstrates a low-cost green synthesis technique to prepare the α-V2O5 phase using Aloe Vera leaf extract. X-ray diffraction technique confirmed the formation of the orthorhombic α-V2O5 phase. The prepared α-V2O5 was employed as an electrode material for SC application. During an electrochemical cyclic voltammetry test in Na2SO4 electrolyte, Na+ ions intercalation and de-intercalation processes resulted in a phase transformation of α-V2O5 to NaV3O8. Structural transformation (i.e., orthorhombic to monoclinic crystal structure) and morphological changes were also observed during the electrochemical phase conversion process. This electrochemical phase transformation process improved the overall supercapacitive performance of the α-V2O5 material. Such electrochemically converted NaV3O8 displayed a maximum specific capacitance of 640.1 F g−1 at 0.5 A g−1 with a long cyclic stability. Furthermore, the AC // NaV3O8 asymmetric SC coin cell device delivered a maximum energy density of 62.6 Wh kg−1 and a power density of 7.3 kW kg−1 along with an excellent cycling stability of ∼81 % over 5000 GCD cycles.

Seismic sedimentology response characteristics of nearshore terminal fan in the suning area of Raoyang Sag, Bohai Bay Basin, NE China

A nearshore terminal fan is a special water system formed in arid environments. The characterisation of its thin-channel sand bodies has long been a challenge restricting oil and gas exploration. This study takes the Suning area of the Raoyang Sag as an example and uses the principles of seismic sedimentology to conduct seismic sedimentary research on the nearshore terminal fan of the first member of the Palaeogene Shahejie Formation (Es1) based on three-dimensional seismic, logging, and core analysis. Seven fourth-order sequences (SQV7) were identified within Es1, deposited by a fluvial river system terminating at the contracting bank of a lake. Prograding terminal fan sedimentary facies on a gentle slope zone were observed in the root mean square seismic attributes after spectral decomposition. We have successfully resolved the sandstone within the studied terminal fan system using a 90° phase conversion of the seismic data and red-green-blue (RGB) fusion of the various seismic attributes. The upper subsegment of the Shahejie Formation developed extensive nearshore terminal fan sedimentation, and the seismic sedimentological response characteristics were mainly channel-like and strip-shaped geomorphic systems deposited on gentle slope zones, indicating distributary channels and distal basin sedimentation. This study enriches our understanding of nearshore fans and provides ideas for predicting favourable sand bodies in this type of sedimentary facies.

Rapid Conversion from Alloy Nanoparticles to Oxide Nanowires: Strain Wave-Driven Ru-O-Mn Collaborative Catalysis for Durable Oxygen Evolution Reaction.

Metal-doped ruthenium oxides with low prices have gained widespread attention due to their editable compositions, distorted structures, and diverse morphologies for electrocatalysis. However, the mainstream challenge lies in breaking the so-called seesaw relationship between activity and stability during acidic oxygen evolution reaction (OER). Herein, strain wave-featured Mn-RuO2 nanowires (NWs) with asymmetric Ru-O-Mn bonds are first fabricated by thermally driven rapid solid phase conversion from RuMn alloy nanoparticles (NPs) at moderate temperature (450 °C). In 0.5M H2SO4, the resultant NWs display a surprisingly ultralow overpotential of 168mV at 10mA cm-2 and run at a stable cell voltage (1.67V) for 150h at 50mA cm-2 in PEMWE, far exceeding IrO2||Pt/C assemble. The simultaneous enhancement of both activity and stability stems from the presence of dense strain waves composed of alternating compressive and tensile ones in the distorted NWs, which collaboratively activate the Ru-O-Mn sites for faster OER. More importantly, the atomic strain waves trigger dynamic Ru-O-Mn regeneration via the refilling of oxygen vacancies by oxyanions adsorbed on adjacent Mn and Ru sites, achieving long-term stability. This work opens a door to designing non-precious metal-assisted ruthenium oxides with unique strains for practical application in commercial PEMWE.

Organic sandwich-structured carbon fiber/SiO2/PES electrochemical membrane with significantly improved charge transfer efficiency and water permeability

Electrochemical membrane separation has the potential for good degradation efficiency and mitigates membrane fouling. However, it is still a real challenge to further build stable organic substrate and improve its charge efficiency. In this study, an electric conductive and sandwich-structured carbon fiber/SiO2/polyether sulfone (CF/SiO2/PES) membrane showing good tetracycline (TC) removal at both acidic (pH = 3) and alkaline (pH = 9) conditions was fabricated by a facile phase conversion method. The CF/SiO2/PES membrane exhibited notably improved water permeability, augmented by 42 % higher with external voltage than that of the membrane without voltage assistance. Furthermore, the CF/SiO2/PES membrane performance in TC removal was systematically assessed under diverse conditions, encompassing TC concentration, pH values, and applied voltage. The membrane displayed a good removal efficiency of 93.6 % and 91.8 % for TC at acidic and alkaline conditions, respectively. Additionally, the degradation pathway of TC was proposed. Crucially, the CF/SiO2/PES membrane exhibited exceptional reusability and stability over eight consecutive runs. Mechanism study proved that the reactive species play a key role in the TC degradation during electro-filtration. The exceptional permeability, removal efficiency, and recyclability position the CF/SiO2/PES membrane as a promising solution for antibiotic wastewater treatment.

Inhibiting phase conversion and improving cyclic stability of Ni-rich layered oxide by high-valence element concentration gradient doping

Nickel (Ni)-rich layered oxide cathodes are believed to be one of the crucial materials for the development of high-energy density power batteries. However, accompanied by the Ni content of layered cathodes increases, it encounters some awkward issues such as sensitivity to moisture, side reactions, and gas production. Herein, by using a high-valency elements Tellurium (Te) doping strategy, we successfully design and fabricate the layered oxide cathode material Li[(Ni0.90Co0.10)0.99Te0.01]O2 (1.0 Te-NC90) with a high capacity of 231.36 mAh g−1 at 0.1C, which has high cycling stability of 95.01 % after 100 cycles at 0.5C, good thermal stability of 205 °C and high Li+ diffusion rate of 8.12 × 10−10 cm2 s−1. It has been found that the (003) interplanar spacing of 1.0 Te-NC90 cathode will increase from 0.472 nm to 0.491 nm due to the concentration gradient Te-doping strategy, which can promote Li+ diffusion. Besides, it can refine the grain structure and transform the primary particles from bulk-grained to rod-grained morphology, and these elongated and closely packed particles radiate from the center to the surface with a spoke-like arrangement, which effectively dissipates lattice strain generated during deeply charging states and suppresses the abrupt lattice transformation associated with the H2 → H3 phase, thereby avoiding the development of microcracks during cycling. In the meantime, robust Te-O bonds can keep the material lattice stable to prevent oxygen loss and TM ion movement. Therefore, this study reveals the significant role of trace Te-doping in enhancing crystal structure and electrochemical stability through microstructural engineering for the control of primary particle morphology.

Flexible Composite Electrolyte Membranes with Fast Ion Transport Channels for Solid-State Lithium Batteries.

Numerous endeavors have been dedicated to the development of composite polymer electrolyte (CPE) membranes for all-solid-state batteries (SSBs). However, insufficient ionic conductivity and mechanical properties still pose great challenges in practical applications. In this study, a flexible composite electrolyte membrane (FCPE) with fast ion transport channels was prepared using a phase conversion process combined with in situ polymerization. The polyvinylidene fluoride-hexafluoro propylene (PVDF-HFP) polymer matrix incorporated with lithium lanthanum zirconate (LLZTO) formed a 3D net-like structure, and the in situ polymerized polyvinyl ethylene carbonate (PVEC) enhanced the interface connection. This 3D network, with multiple rapid pathways for Li+ that effectively control Li+ flux, led to uniform lithium deposition. Moreover, the symmetrical lithium cells that used FCPE exhibited high stability after 1200 h of cycling at 0.1 mA cm-2. Specifically, all-solid-state lithium batteries coupled with LiFePO4 cathodes can stably cycle for over 100 cycles at room temperature with high Coulombic efficiencies. Furthermore, after 100 cycles, the infrared spectrum shows that the structure of FCPE remains stable. This work demonstrates a novel insight for designing a flexible composite electrolyte for highly safe SSBs.

Synthesis and morphological control of Ca5(PO4)3Cl and Ca2PO4Cl via the phase transformation of amorphous calcium phosphate in molten chlorides

In the present work, the phase conversion of amorphous calcium phosphate (ACP) in different molten chlorides (LiCl, NaCl, KCl, CaCl2) was investigated in detail. The main synthesis parameters influencing the phase purity and morphological features of the products include the chemical composition of molten salts, the heat treatment temperature and the ACP-to-flux ratio. The selective synthesis of single-phase Ca5(PO4)3Cl or Ca2PO4Cl depends on the content of CaCl2 in the reaction medium. The morphology control of Ca5(PO4)3Cl powders was achieved by varying the KCl/CaCl2 ratio in the flux, resulting in the formation of the particles of different size and shape. The KCl-rich fluxes led to the formation of relatively small nearly spherical particles, whereas the CaCl2-rich fluxes promoted an anisotropic growth of the Ca5(PO4)3Cl crystals resulting in the formation of monodispersed hexagonally-shaped microrods. Whereas the anisotropic growth was observed at relatively low temperature (750 °C) the increase of the reaction temperature up to 1200 °C significantly reduced this effect leading to the formation of the particles with obviously low aspect ratio. The phase crystallinity and purity were analyzed using powder X-ray diffraction, FTIR spectroscopy as well as 31P, 35Cl and 1H solid-state NMR. The morphological features and chemical composition of the synthesized products were studied by SEM/EDX analysis.

Dimethylamine oxalate manipulating CsPbI3 perovskite film crystallization process for high efficiency carbon electrode based perovskite solar cells

Crystallization process determines the quality of perovskite films and the performances of resultant perovskite solar cells (PSCs). Dimethylamine oxalate has been proven as a multifunctional modulator, and is explored as an efficient additive in manipulating the crystallization process of CsPbI3 perovskite films. On one hand, oxalate serves as the precipitator that facilitates the nucleation process of intermediate. The larger size of intermediate is conductive to the larger size and smaller grain boundaries of resultant perovskite. On the other hand, in subsequent annealing process, the phase conversion and growth process of transient perovskite can be decelerated due to the strong interactions of oxalate with both dimethylamine cation (DMA+) and Pb2+. Due to the optimized crystallization kinetics, the morphology and quality of CsPbI3 perovskite films are comprehensively improved with lower defect concentrations, and charge recombination loss is effectively suppressed. Benefiting from the optimized crystal quality of perovskite films, the carbon electrode-based CsPbI3 PSCs exhibit a champion efficiency of 18.48%. This represents one of the highest levels among all hole transport layer-free inorganic perovskite solar cells.

Novel high-voltage cathode for aqueous zinc ion batteries: Porous K0.5VOPO4·1.5H2O with reversible solid-solution intercalation and conversion storage mechanism

Cathode materials that possess high output voltage, as well as those that can be mass-produced using facile techniques, are crucial for the advancement of aqueous zinc-ion battery (ZIBs) applications. Herein, we present for the first time a new porous K0.5VOPO4·1.5H2O polyanionic cathode (P-KVP) with high output voltage (above 1.2 V) that can be manufactured at room temperature using straightforward coprecipitation and etching techniques. The P-KVP cathode experiences anisotropic crystal plane expansion via a sequential solid-solution intercalation and phase conversion pathway throughout the Zn2+ storage process, as confirmed by in-situ synchrotron X-ray diffraction and ex-situ X-ray photoelectron spectroscopy. Similar to other layered vanadium-based polyanionic materials, the P-KVP cathode experiences a progressive decline in voltage during the cycle, which is demonstrated to be caused by the irreversible conversion into amorphous VOx. By introducing a new electrolyte containing Zn(OTF)2 to a mixed triethyl phosphate and water solution, it is possible to impede this irreversible conversion and obtain a high output voltage and longer cycle life by forming a P-rich cathode electrolyte interface layer. As a proof-of-concept, the flexible fiber-shaped ZIBs based on modified electrolyte woven into a fabric watch band can power an electronic watch, highlighting the application potential of P-KVP cathode.