Chalcopyrite-Derived NaxMO2 (M = Cu, Fe, Mn) Cathode: Tuning Impurities for Self-Doping

Turning harmful Mn2+ to treasure: In-situ formed ε-MnO2 for removing heavy metals from acid mine drainage

Acid mine drainage (AMD) contains high concentrations of heavy metals, causing serious environmental pollution. Current neutralization techniques fail to recover and utilize valuable heavy metals, and generate large quantities of hazardous sludge. Manganese (Mn) is generally present at high levels in AMD. Therefore, this paper proposed a technology to recover Mn from AMD, by adding KMnO4 to converting Mn into ε-MnO2. Ultra-Violet C (UVC) was used to photolyze the residual KMnO4. The study then evaluated the processes and mechanisms involved in the technology. The photolysis of KMnO4 in strong acidic conditions was determined, and new mechanisms were proposed. MnO2 produced by the photolysis process was formed through the reaction between Mn(III) and KMnO4. In the absence of KMnO4, Mn(III) underwent further photolysis and was reduced to Mn2+. The maximum adsorption capacities of in-situ formed ε-MnO2 for Pb2+, Cd2+, and Fe3+ were 449.80, 122.05, and 779.88 mg/g, respectively. Higher Mn-OH levels and MnO2 regeneration were crucial in improving adsorption performance. Proton exchange and inner-circle complexation were the main pathways for Pb2+ and Cd2+ adsorption by in-situ formed ε-MnO2. A phase transformation occurred when a substantial amount of Fe3+ was adsorbed, leading to the gradual transformation to MnFe binary oxides. When applying in-situ formed ε-MnO2 technology for actual AMD treatment, 98.62 % of Mn in AMD was recovered within 24 h in the presence of ε-MnO2 for possible further reuse in industries, with a final recovery of 0.76 kg/m3. Further, this technique removed other heavy metals and reduced the sludge volume by 20.99 % when used as a pre-treatment step for neutralization. These results demonstrated the broad potential of this treatment technology.

High Voltage Ga-Doped P2-Type Na2/3 Ni0.2 Mn0.8 O2 Cathode for Sodium-Ion Batteries

Ni/Mn-based oxide cathode materials have drawn great attention due to their high discharge voltage and large capacity, but structural instability at high potential causes rapid capacity decay. How to moderate the capacity loss while maintaining the advantages of high discharge voltage remains challenging. Herein, the replacement of Mn ions by Ga ions is proposed in the P2-Na2/3 Ni0.2 Mn0.8 O2 cathode for improving their cycling performances without sacrificing the high discharge voltage. With the introduction of Ga ions, the relative movement between the transition metal ions is restricted and more Na ions are retained in the lattice at high voltage, leading to an enhanced redox activity of Ni ions, validated by ex situ synchrotron X-ray absorption spectrum and X-ray photoelectron spectroscopy. Additionally, the P2-O2 phase transition is replaced by a P2-OP4 phase transition with a smaller volume change, reducing the lattice strain in the c-axis direction, as detected by operando/ex situ X-ray diffraction. Consequently, the Na2/3 Ni0.21 Mn0.74 Ga0.05 O2 electrode exhibits a high discharge voltage close to that of the undoped materials, while increasing voltage retention from 79% to 93% after 50 cycles. This work offers a new avenue for designing high-energy density Ni/Mn-based oxide cathodes for sodium-ion batteries.

Nano-Ni/Co-PBA as high-performance cathode material for aqueous sodium-ion batteries

Prussian blue analogues (PBAs) are reliable and promising cathode materials for aqueous sodium-ion batteries (ASIBs) owing to their open three-dimensional frameworks, outstanding stability, and low production costs. However, PBAs containing only a single type of transition-metal ion often have limited charge-storage capacities in aqueous systems. This study reports the first example of K0.11Ni0.39Co0.79[Fe(CN)6]·2.04H2O nanoparticles (Ni/Co-PBA) being used as a high-capacity cathode material for ASIBs. Owing to multi-electron redox reactions involving Co and Fe ions, Ni/Co-PBA has an initial capacity of 65 mAh g-1and a capacity retention rate of 80% after 1000 cycles at 1.0 A g-1, indicating its outstanding cycle performance and capacity retention. Ex-situ x-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique were used to analyze the redox mechanisms and kinetics of Ni/Co-PBA. Ni/Co-PBA-based ASIBs are among the most promising energy-storage technologies for large-scale fixed energy-storage systems because of their outstanding electrochemical performance, low costs, and high efficiency.

Defect-Induced Self-Poling in a W18O49/PVDF Piezoelectric Energy Harvester

W₁₈O₄₉ nanostructures, previously used for electrocatalysis, energy storage, electrochromic, and gas sensing applications, are incorporated in poly(vinylidene fluoride) (PVDF) in this work for mechanical energy-harvesting applications. X-ray diffraction spectroscopy (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and the polarization-electric (P-E) field loop test prompts the addition of W₁₈O₄₉ nanorods in PVDF nucleates and stabilizes the piezoelectric polar γ-phase in the nanocomposite. Electrochemical experiments were employed for the first time to relate the event of the evolution of crystalline phases in PVDF to the transfer of electrons to the electrolyte from PVDF using the data from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). High dielectric constant (ε') and low dielectric loss (ε″) values were obtained proportionately for different weight percentage additions of W₁₈O₄₉ nanorods in PVDF. DSC was employed to study the crystallization kinetics of γ-phase evolution. Piezoresponse force microscopy (PFM) was used to compare the piezoelectric responses from the PVDF nanocomposites. The W₁₈O₄₉/PVDF nanocomposite could generate a peak open circuit voltage of ∼6 V and a peak short circuit current of ∼700 nA. The W₁₈O₄₉/PVDF nanocomposite could light two commercial blue-light-emitting diodes (LEDs) with hand impulse imparting.

Structure and Performance of NaxMn0.85Al0.1Fe0.05O2 (0.7 ≤ x ≤ 1.0) Composite Materials for Sodium-Ion Batteries

P2 and O3 structures are two important sodium manganese oxide phases for sodium-ion batteries; however, encounter Na-deficient and poor rate performance, respectively. Herein, a systematic study of Na_xMn_0.85Al_0.1Fe_0.05O₂ (0.7 ≤ x ≤ 1.0) materials is performed by employing solid-state NMR, X-ray diffraction, and electrochemical analysis, to provide an in-depth understanding on the structure and the correlated performance for the rational design. The interlayer spacing of α-NaMnO₂ broadens, and the content of distorted O3 structures (α- and β-NaMnO₂) increases with raising Na content. It is exhibited that the NaMn_0.85Al_0.1Fe_0.05O₂ composite material presents better rate and cycling performance than P2-type Na_0.7Mn_0.85Al_0.1Fe_0.05O₂, delivering a capacity of 87 mAh g^-1 at 5 C. Significantly, the determinants of performance are further discussed, which reveal that diffusion coefficient is probably not the decisive factor restricts the rate performance of O3 and composite materials. The phase transition relaxation and the interfacial charge transfer resistance should be seriously addressed for further improvement.

K-Ion Battery Cathode Design Utilizing Trigonal Prismatic Ligand Field

The intrinsic physical and chemical properties of materials are largely governed by the bonding and electronic structures of their fundamental building units. The majority of cathode materials contain octahedral TMO₆ (TM = transition metal), which dominates the redox chemistry during electrochemical operation. As a less symmetric form of TMO₆ , the trigonal prismatic geometry is not a traditionally favored coordination configuration as it tends to lose the crystal-field stabilization energy and thus generate large ligand repulsion. Herein, a K-ion battery cathode design, K₂ Fe(C₂ O₄ )₂ , is shown​, where the TMO₆ trigonal prism (TP) is not only electrochemically active but stable enough to allow for excellent cycling stability. Detailed synchrotron X-ray absorption spectroscopy measurements reveal the evolution of localized fine structure, evidencing the electrochemical activity, reversibility, and stability of the TP motif. The findings are expected to expand the toolbox for the rational design of electrode materials by taking advantage of TP as a structural gene.

Recent advances in waste water treatment through transition metal sulfides-based advanced oxidation processes

With the ever-growing water pollution issues, advanced oxidation processes (AOPs) have received growing attention due to their high efficiency in the removal of refractory organic pollutants. Transition metal sulfides (TMSs), with excellent optical, electrical, and catalytical performance, are of great interest as heterogeneous catalysts. These TMSs-based heterogeneous catalysts have been demonstrated to becapable and adaptable in water purification through advanced oxidation processes. The aim of this review is to conduct an exhaustive analysis and summary of recent progress in the application of TMSs-based AOPs for water decontamination. Firstly, the commonly used tuning strategies for TMSs-based catalysts are concisely introduced, including artificial size and shape control, composition control, doping, and heterostructure manufacturing. Then, a comprehensive overview of the current state-of-the-art progress on TMSs-based AOPs (i.e., Fenton-like oxidation, photocatalytic oxidation, and electro chemical oxidation processes) for wastewater treatment is discussed in detail, with an emphasis on their catalytic performance and involved mechanism. In addition, influencing factors of water chemistry, namely, pH, temperature, dissolved oxygen, inorganic species, and natural organic matter on the catalytic performance of established AOPs are analyzed. Furthermore, the reusability and stability of TMSs-based catalysts in these AOPs are also outlined. Finally, current challenges and future perspectives related to TMSs-based catalysts and their applications for AOPs wastewater treatment are proposed. It is expected that this review would shed some light on the future development of TMSs-based AOPs towards water purification.

Dual-Strategy of Cation-Doping and Nanoengineering Enables Fast and Stable Sodium-Ion Storage in a Novel Fe/Mn-Based Layered Oxide Cathode

Iron/manganese-based layered transition metal oxides have risen to prominence as prospective cathodes for sodium-ion batteries (SIBs) owing to their abundant resources and high theoretical specific capacities, yet they still suffer from rapid capacity fading. Herein, a dual-strategy is developed to boost the Na-storage performance of the Fe/Mn-based layered oxide cathode by copper (Cu) doping and nanoengineering. The P2-Na0.76Cu0.22Fe0.30Mn0.48O2 cathode material synthesized by electrospinning exhibits the pearl necklace-like hierarchical nanostructures assembled by nanograins with sizes of 50-150 nm. The synergistic effects of Cu doping and nanotechnology enable high Na+ coefficients and low ionic migration energy barrier, as well as highly reversible structure evolution and Cu/Fe/Mn valence variation upon repeated sodium insertion/extraction; thus, the P2-Na0.76Cu0.22Fe0.30Mn0.48O2 nano-necklaces yield fabulous rate capability (125.4 mA h g-1 at 0.1 C with 56.5 mA h g-1 at 20 C) and excellent cyclic stability (≈79% capacity retention after 300 cycles). Additionally, a promising energy density of 177.4 Wh kg-1 is demonstrated in a prototype soft-package Na-ion full battery constructed by the tailored nano-necklaces cathode and hard carbon anode. This work symbolizes a step forward in the development of Fe/Mn-based layered oxides as high-performance cathodes for SIBs.

Revisiting of Tetragonal NaVPO4F: A High Energy Density Cathode for Sodium-Ion Batteries

Tetragonal NaVPO₄F has been regarded as an ideal cathode for sodium-ion batteries because of its high average plateau (3.8 V) and theoretical specific capacity (143 mA h g^-1). However, the Na-storage performance is still hindered by unsatisfying thermal stability and poor conductivity. Herein, a stable tetragonal NaVPO₄F has been synthesized by a novel solvent thermal method using a carbon coating precursor. The as-prepared NaVPO₄F@C nanocomposite delivers a capacity of 133 mA h g^-1 at 0.2 C, corresponding to an excellent energy density of 509 W h kg^-1; when coupled with an HC anode, the full cell still displays an outstanding performance of 124 mA h g^-1 at 0.05 C. Fast Na⁺ diffusion kinetics (D^Na+ = 10^-12 to 10^-10 cm² s^-1) and small volume change (4.4%) are exploited, which ensures good rate trait and cycling stability of tetragonal NaVPO₄F. Further, the Na⁺ extraction-insertion mechanism has been explored by analyzing the crystal structure change during in situ X-ray powder diffraction cycles.

Long-lifespan Polyanionic Organic Cathodes for Highly Efficient Organic Sodium-ion Batteries

An organic Na-ion battery is reported with a polyanionic 9,10-anthraquinone-2,6-disulfonate (Na₂ AQ26DS, 130 mAh g^-1 ) cathode and the Na-intercalated state (Na₄ TP) of sodium terephthalate (Na₂ TP, 255 mAh g^-1 ) as the anode. The resulting full cells deliver the maximum discharge capacity of 131 mAh g^-1 _cathode in 0.5-3.2 V, simultaneously maintaining the average value of ≈62 mAh g^-1 _cathode during 1200 cycles (0.5 A g^-1 , ≈4 C). These results are among the best performing organic sodium-ion full cells reported to date.

Electrode Design for High-Performance Sodium-Ion Batteries: Coupling Nanorod-Assembled Na3V2(PO4)3@C Microspheres with a 3D Conductive Charge Transport Network

As one of the most promising cathodes for sodium-ion batteries, the polyanionic compounds still suffer from unsatisfactory capacity and rate performance resulting from poor electron conductivity. Furthermore, the charge-transfer kinetics, especially for Na⁺, becomes limiting as the mass loading increases. Herein, a robust free-standing electrode coupling optimal porous Na₃V₂(PO₄)₃@C microspheres with a bicontinuous charge transport network is designed and prepared by a simple casting method. In the design, the optimal porous carbon-coated microspheres, composed of some continuous nanorods, along with interwoven carbon nanofiber networks offer efficient electron transport and facile ion diffusion. Such an elaborate design enables impressive electron/ion conductivity, contributing to remarkable rate performance (116.1 mA h g^-1 at 0.2 C; 96 mA h g^-1 at 30 C) and outstanding cycling stability (90% capacity retention in 500 cycles at 1 C; 80% capacity retention in 5000 cycles at 10 C), which has surpassed other similar Na₃V₂(PO₄)₃-based free-standing electrodes as reported. More importantly, when mass loading extends to 8 mg cm^-2, an excellent capacity retention of 75% at 10 C can be obtained. The research offers a new avenue into the rational design of porous microspheres electrode with high conductive charge transport network, indicating its superiority in practical applications.

Defect Rich Hierarchical Porous Carbon for High Power Supercapacitors

Tuning hierarchical pore structure of carbon materials is an effective way to achieve high energy density under high power density of carbon-based supercapacitors. However, at present, most of methods for regulating pores of carbon materials are too complicated to be achieved. In this work, a durian shell derived porous carbon (DSPC) with abundant porous is prepared through chemical activation as a defect strategy. Hierarchical porous structure can largely enhance the transfer rate of electron/ion. Furthermore, DSPC with multiple porous structure exhibits excellent properties when utilized as electrode materials for electric double layer capacitors (EDLCs), delivering a specific capacitance of 321 F g-1 at 0.5 A g-1 in aqueous electrolyte. Remarkably, a high energy density of 27.7 Wh kg-1 is obtained at 675 W kg-1 in an organic two-electrode device. And large capacity can be remained even at high charge/discharge rate. Significantly, hierarchical porous structure allows efficient ion diffusion and charge transfer, resulting in a prominent cycling stability. This work is looking forward to providing a promising strategy to prepare hierarchical porous carbon-based materials for supercapacitors with ultrafast electron/ion transport.