Potassium mediated Co-Fe-based Prussian blue analogue architectures for aqueous potassium-ion storage

Bismuth: An Epitaxy-like Conversion Mechanism Enabled by Intercalation-Conversion Chemistry for Stable Aqueous Chloride-Ion Storage

The exploitation of new anion battery systems based on high-abundance oceanic elements (e.g., F-, Cl-, and Br-) is a strong supplement to the current metal cation (e.g., Li+, Na+) battery technologies. Bismuth (Bi), the rare anion-specific anode species nearest to practical application for chloride ion storage, is plagued by volume expansion and structure collapse due to limited control of its conversion behavior. Here, we reveal that a unique epitaxy-like conversion mechanism in the monocrystalline Bi nanospheres (R3m group) can drastically inhibit grain pulverization and capacity fading, which is enabled by Cl- intercalation in their interlayer space. The Bi nanosphere anode can self-evolve and transform into a rigid BiOCl nanosheet-interlaced structure after the initial conversion reaction. With this epitaxy-like conversion mechanism, the Bi anode exhibits a record-high capacity of 249 mAh g-1 (∼1.2 mAh cm-2) at 0.25 C and sustains more than 1400 h with 20% capacity loss. Pairing this anode with a Prussian blue cathode, the full battery can deliver an ultrahigh desalination capacity of 127.1 m gCl gBi-1. Our study milestones the understanding of conversion-type anode structures, which is an essential step toward the commercialization of aqueous batteries.

Regioselective super-assembly of Prussian blue analogue

The construction of high-asymmetrical structures demonstrates significant potential in improving the functionality and distinctness of nanomaterials, but remains a considerable challenge. Herein, we develop a one-pot method to fabricate regioselective super-assembly of Prussian blue analogue (PBA) -- a PBA anisotropic structure (PBA-AS) decorated with epitaxial modules--using a step-by-step epitaxial growth on a rapidly self-assembled cubic substrate guided by thiocyanuric acid (TCA) molecules. The epitaxial growth units manifest as diverse geometric shapes, which are predominantly concentrated on the {100}, {111}, or {100}+{111} crystal plane of the cubic substrate. The crystal plane and morphology of epitaxial module can be regulated by changing the TCA concentration and reaction temperature, enabling a high level of controllability over specific assembly sites and structures. To illustrate the advantage of the asymmetrical structure, phosphated PBA-AS demonstrates improved performance in the oxygen evolution reaction compared to simple phosphated PBA nanocube. This method offers valuable insights for designing asymmetrical nanomaterials with intricate architectures and versatile functionalities.

Wireless wearable potentiometric sensor for simultaneous determination of pH, sodium and potassium in human sweat

This paper reports on the development of a flexible-wearable potentiometric sensor for real-time monitoring of sodium ion (Na+), potassium ion (K+), and pH in human sweat. Na0.44MnO2, polyaniline, and K2Co[Fe(CN)6] were used as sensing materials for Na+, H+ and K+ monitoring, respectively. The simultaneous potentiometric Na+, K+, and pH sensing were carried out by the developed sensor, which enables signal collection and transmission in real-time to the smartphone via a Wi-Fi access point. Then, the potentiometric responses were evaluated by a designed android application. Na+, K+, and pH sensors illustrated high sensitivity (59.7 ± 0.8 mV/decade for Na+, 57.8 ± 0.9 mV/decade for K+, and 54.7 ± 0.6 mV/pH for pH), excellent stability, and good batch-to-batch reproducibility. The results of on-body experiments demonstrated that the proposed platform is capable of real-time monitoring of the investigated ions.

Intercalating a potassium-aqua complex cation into an α-MoO3 layer without reducing molybdenum: a potential storage system

We have demonstrated a green aqueous synthesis of rod-shaped MoO3 material, [MoVI3O9{K(H2O)4}(CH3COO)]·H2O (2) intercalating potassium-aqua-complex acetate into its lamellar space, simply by ion-exchange of Co(II)-aqua-complex in compound [MoVI4O12(CH3COO)2{CoII(H2O)6}]·2H2O (1) by {K(H2O)4}+ in an aqueous solution of 1 and KCl. Compound 2 acts as a potential storage system of alkali metal ions.

Intercalation pseudocapacitance mechanism realizes high-performance cathode for aqueous potassium ion batteries

Aqueous potassium-ion batteries have garnered significant interest due to their eco-friendly characteristics and affordability. However, The suboptimal lifetime and restricted energy density of electrode materials present considerable obstacles to the advancement of aqueous potassium ion batteries. In this paper, we report a Ce doped MnO2 material (Ce-MnO2). Ce-MnO2 with large lattice spacing and abundant oxygen defects successfully triggered the intercalation pseudocapacitance behavior in aqueous potassium ion batteries. The intercalation pseudocapacitance mechanism gives MnO2 good capacity and enhanced stability. The Ce-MnO2 demonstrates a high discharge capacity of 120 mAh g-1 at 1 A g-1 with a low concentration electrolyte. It also has a capacity retention rate of 82.5% at 2000 cycles at 5 A g-1. The application of the intercalation pseudocapacitance mechanism offers a new approach to addressing the challenges associated with aqueous potassium-ion batteries.

Nano-Impact Electrochemistry Reveals Kinetics Information of Metal-Ion Battery Materials with Multiple Redox Centers

Prussian blue (PB) has emerged as a promising cathode material in aqueous batteries. It possesses two distinct redox centers, and the potassium ions (K+ ) are unevenly distributed throughout the compound, adding complexity to the interpretation of the K+ insertion/de-insertion kinetic mechanism. Traditional ensemble-averaged measurements are limited in uncovering the precise kinetic information of the PB particles, as the results are influenced by the construction of the porous composite electrode and the redox behavior from different particles. In this study, the electrochemical processes of individual PB particles were investigated using nano-impact electrochemistry. By varying the potentials, different types of transient current signals were obtained that revealed the kinetic mechanism of each oxidation/reduction reaction in combination with theoretical simulation. Additionally, a partially contradictory conclusion between single-particle analysis and the ensemble-averaged measurement was discussed. These findings contribute to a better understanding of the electrochemical processes of cathode materials with multiple redox centers, which facilitates the development of effective strategies to optimize these materials.

Multilevel spatial confinement of transition metal selenides porous microcubes for efficient and stable potassium storage

Recently, potassium-ion batteries (PIBs) have been considered as one of the most promising energy storage systems; however, the slow kinetics and large volume variation induced by the large radius of potassium ions (K⁺) during chemical reactions lead to inferior structural stability and weak electrochemical activity for most potassium storage anodes. Herein, a multilevel space confinement strategy is proposed for developing zinc-cobalt bimetallic selenide (ZnSe/Co_0.85Se@NC@C@rGO) as high-efficient anodes for PIBs by in-situ carbonizing and subsequently selenizing the resorcinol-formaldehyde (RF)-coated zeolitic imidazolate framework-8/zeolitic imidazolate framework-67 (ZIF-8/ZIF-67) encapsulated into 2D graphene. The highly porous carbon microcubes derived from ZIF-8/ZIF-67 and carbon shell arising from RF provide rich channels for ion/electron transfer, present a rigid skeleton to ensure the structural stability, offer space for accommodating the volume change, and minimize the agglomeration of active material during the insertion/extraction of large-radius K⁺. In addition, the three-dimensional (3D) carbon network composed of graphene and RF-derived carbon-coated microcubes accelerates the electron/ion transfer rate and improves the electrochemical reaction kinetics of the material. As a result, the as-synthesized ZnSe/Co_0.85Se@NC@C@rGO as the anode of PIBs possesses the excellent rate capability of 203.9 mA h g^-1 at 5 A g^-1 and brilliant long-term cycling performance of 234 mA h g^-1 after 2,000 cycles at 2 A g^-1. Ex-situ X-ray diffraction (Ex-situ XRD) diffraction reveals that the intercalation/de-intercalation of K⁺ proceeds through the conversion-alloying reaction. The proposed strategy based on the spatial confinement engineering is highly effective to construct high-performance anodes for PIBs.

Free-Standing Carbon Nanofiber Composite Networks Derived from Bacterial Cellulose and Polypyrrole for Ultrastable Potassium-Ion Batteries

Carbon materials derived from bacterial cellulose have been studied in lithium-ion batteries due to their low cost and flexible characteristics. However, they still face many intractable problems such as low specific capacity and poor electrical conductivity. Herein, bacterial cellulose is used as the carrier and skeleton to creatively realize the composite of polypyrrole on its nanofiber surface. After carbonization treatment, three-dimensional carbon network composites with a porous structure and short-range ordered carbon are obtained for potassium-ion batteries. The introduction of nitrogen doping from polypyrrole can increase the electrical conductivity of carbon composites and provide abundant active sites, improving the comprehensive performance of anode materials. The carbonized bacterial cellulose@polypyrrole (C-BC@PPy) anode exhibits a high capacity of 248 mA h g^-1 after 100 cycles at 50 mA g^-1 and a capacity retention of 176 mA h g^-1 even over 2000 cycles at 500 mA g^-1. Combined with density functional theory calculations, these results indicate that the capacity of C-BC@PPy is contributed by N-doped and defect carbon composite materials as well as pseudocapacitance. This study provides a guideline for the development of novel bacterial cellulose composites in the energy storage field.

Incorporating Near-Pseudocapacitance Insertion Ni/Co-Based Hexacyanoferrate and Low-Cost Metallic Zn for Aqueous K-Ion Batteries

The limited availability of cathode materials with high specific capacity and significant cycling stability for aqueous K-ion batteries (AKIBs) hinder their further development owing to the large radius of K⁺ (1.38 Å). Prussian blue and its analogs with a three-dimensional frame structure possessing special energy storage mechanism are promising candidates as cathode materials for AKIBs. In this study, K_0.2 Ni_0.68 Co_0.77 Fe(CN)₆  ⋅ 1.8H₂ O (KNCHCF) was prepared as a cathode material for AKIBs. Both the electrochemical activity of Co ions and the near-pseudocapacitance intercalation of KNCHCF enhance K⁺ storage. Therefore, KNCHCF exhibits a superior capacity maintenance rate of 86 % after 1000 cycles at a high current density of 3.0 A g^-1 . The storage mechanism of K⁺ in AKIBs was revealed through ex situ X-ray diffraction, ex situ Fourier transform infrared spectroscopy, and ex situ X-ray photoelectron spectroscopy measurements. Moreover, the assembled K-Zn hybrid battery showed good cycling stability with 93.1 % capacity maintenance at 0.1 A g^-1 after 50 cycles and a high energy density of 96.81 W h kg^-1 . Hence, KNCHCF may be a potential material for the development of AKIBs.

Dual stabilization in potassium Prussian blue and cathode/electrolyte interface enables advanced potassium-ion full-cells

Potassium Prussian Blue (KPB) have been investigated as promising cathode materials for potassium-ion batteries. However, numerous structure defects and side reactions at electrode/electrolyte interface will deteriorate the electrochemical properties. Herein, dual stabilization strategy of structure of KPB particles and cathode/electrolyte interface is reported to enhance the capacity and electrochemical stability. The structure of KPB is stabilized through inhibiting nucleation and growth by addition of ethylenediaminetetraacetic acid dipotassium salt during co-precipitation, which can enlarge the particle size. Meanwhile, stabilizing the cathode/electrolyte interface via changing potassium hexafluorophosphate to potassium bis (fluorosulfonyl) imide (KFSI) electrolyte can further reduce side reactions to boost the coulombic efficiency of KPB cathode. Benefiting from dual engineering in structure of KPB and cathode/electrolyte interface, the half-cell in KFSI electrolyte possesses two discharge potential plateaus at 3.4 and 4.0 V with reversible capacity of 92.7 mAh g^-1 at 0.03 A g^-1. To demonstrate its practical use, KPB//graphite full-cell device is successfully constructed, exhibiting the capacity up to 102.4 mAh g^-1 at 0.1 A g^-1, high-rate (40.4 mAh g^-1 at 1.5 A g^-1) and superior cyclic stability (88% capacity retention from cycle 25 to 400 at 1 A g^-1). This work provides a synergetic engineering strategy to realize the powerful application of high-performance potassium-ion full-cell devices in energy storage.

Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue FeII/CoIII Cube in Aqueous Solution: A Kineticomechanistic Exchange Study

The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{Co^III(Me₃-tacn)}₄{Fe^II(CN)₆}₄]^4- (Me₃-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H⁺] to 2 M [OH^-]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH₂}⁺ (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH₂}⁺ or M⁺ units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs⁺ cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH₂}⁺ units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li⁺ solution.

Interconnected MoS2 on 2D Graphdiyne for Reversible Sodium Storage

In this study, graphdiyne (GDY) was first reported as a substrate material for sodium-ion batteries (SIBs). The creative hybridization of GDY and molybdenum disulfide (MoS₂) endows the composite with unique heterostructural and morphological advantages that boost the charge transport rate and enhance the battery discharge properties. Electrochemical results indicated that the MoS₂@GDY anode displays a considerable discharge capacity of up to 328 mAh g^-1 at 1000 mA g^-1. A capacity retention of 93% even at testing current back to 200 mA g^-1 suggests superior rate characteristics. An outstanding stable cyclic performance of 217 mAh g^-1 is obtained at a high testing density. The attractive results not only demonstrate that GDY could be used not only as an effective conductive substrate to prevent the host material from agglomerating in the electrochemical process but also provide a novel design for fabricating efficient electrode materials for future energy-storage systems.