Synergistic Interface-Assisted Electrode–Electrolyte Coupling Toward Advanced Charge Storage

Owing to the limited charge storage capability of transitional metal oxides in aqueous electrolytes, the use of redox electrolytes (RE) represents a promising strategy to further increase the energy density of aqueous batteries or pseudocapacitors. The usual coupling of an electrode and an RE possesses weak electrode/RE interaction and weak adsorption of redox moieties on the electrode, resulting in a low capacity contribution and fast self-discharge. In this work, Fe(CN)₆⁴⁻ groups are grafted on the surface of Co₃O₄ electrode via formation of Co N bonds, creating a synergistic interface between the electrode and the RE. With such an interface, the coupled Co₃O₄–RE system exhibits greatly enhanced charge storage from both Co₃O₄ and RE, delivering a large reversible capacity of ≈1000 mC cm⁻² together with greatly reduced self-discharge. The significantly improved electrochemical activity of Co₃O₄ can be attributed to the tuned work function via charge injection from Fe(CN)₆⁴⁻, while the greatly enhanced adsorption of K₃Fe(CN)₆ molecules is achieved by the interface induced dipole–dipole interaction on the liquid side. Furthermore, this enhanced electrode–electrolyte coupling is also applicable in the NiO–RE system, demonstrating that the synergistic interface design can be a general strategy to integrate electrode and electrolyte for high-performance energy storage devices.     

A High‐Energy and Long‐Life Aqueous Zn/Birnessite Battery via Reversible Water and Zn2+ Coinsertion

Aqueous rechargeable Zn/birnessite batteries have recently attracted extensive attention for energy storage system because of their low cost and high safety. However, the reaction mechanism of the birnessite cathode in aqueous electrolytes and the cathode structure degradation mechanics still remain elusive and controversial. In this work, it is found that solvation water molecules coordinated to Zn²⁺ are coinserted into birnessite lattice structure contributing to Zn²⁺ diffusion. However, the birnessite will suffer from hydroxylation and Mn dissolution with too much solvated water coinsertion. Through engineering Zn²⁺ primary solvation sheath with strong‐field ligand in aqueous electrolyte, highly reversible [Zn(H₂O)₂]²⁺ complex intercalation/extraction into/from birnessite cathode is obtained. Cathode–electrolyte interface suppressing the Mn dissolution also forms. The Zn metal anode also shows high reversibility without formation of “death‐zinc” and detrimental dendrite. A full cell coupled with birnessite cathode and Zn metal anode delivers a discharge capacity of 270 mAh g^?1, a high energy density of 280 Wh kg^?1 (based on total mass of cathode and anode active materials), and capacity retention of 90% over 5000 cycles.     

High-Voltage Aqueous Na-Ion Battery Enabled by Inert-Cation-Assisted Water-in-Salt Electrolyte

Water-in-salt (WiS) electrolytes provide a new pathway to widen the electrochemical window of aqueous electrolytes. However, their formulation strongly depends on the solubility of the chosen salts, imposing a stringent restriction on the number of possible WiS systems. This issue becomes more severe for aqueous Na-ion batteries (ANIBs) owing to the relatively lower solubility of sodium salts compared to its alkaline cousins (Li, K, and Cs). A new class of the inert-cation-assisted WiS (IC-WiS) electrolytes containing the tetraethylammonium (TEA⁺) inert cation is reported. The Na IC-WiS electrolyte at a superhigh concentration of 31 mol kg^–1 exhibits a wide electrochemical window of 3.3 V, suppresses transition metal dissolution from the cathode, and ensures singular intercalation of Na into both cathode and anode electrodes during cycling, which is often problematic in mixed alkali cation systems such as K–Na and Li–Na. Owing to these unique advantages of the IC-WiS electrolyte, the NaTiOPO₄ anode and Prussian blue analog Na_1.88Mn[Fe(CN)₆]_0.97·1.35H₂O cathode can be coupled to construct a full ANIB, delivering an average voltage of 1.74 V and a high energy density of 71 Wh kg⁻¹ with a capacity retention of 90% after 200 cycles at 0.25C and of 76% over 800 cycles at 1C.     

Oxidation of Np(V) and Np(IV) with Fe(CN) 6 3− ions in carbonate solutions

The formal potential of the Fe(CN) ₆ ^3? /Fe(CN) ₆ ^4? couple in 1 M NaHCO₃ and 1–2 M Na₂CO₃ solutions was determined. It is equal to 505 and 510 mV, respectively, exceeding the potentials of the Np(VI)/(V) and Np(V)/(IV) couples in carbonate solutions. The equilibrium of the reaction Np(V) + Fe(CN) ₆ ^3? = Np(VI) + Fe(CN) ₆ ^4? was studied. Fe(CN) ₆ ^3? ions oxidize Np(IV) to Np(V) and then to Np(VI). The arising Np(VI) oxidizes Np(IV). The Np(IV) oxidation accelerates in going from NaHCO₃ to Na₂CO₃. An increase in [Na₂CO₃] or in the ionic strength (by adding neutral salts) decelerates the oxidation. Np(IV) introduced in an HCl solution reacts with Fe(CN) ₆ ^3? or with Np(VI) faster than Np(IV) introduced in a Na₂CO₃ solution. The activation energy of the reaction of Np(IV) with Fe(CN) ₆ ^4? in the range 20–45°C is 107 kJ mol^?1. The reaction mechanism involves formation of the activated complex from ions of Np(IV) hydroxocarbonate and oxidant.     

An Ultrastable and High‐Performance Flexible Fiber‐Shaped Ni–Zn Battery based on a Ni–NiO Heterostructured Nanosheet Cathode

Currently, the main bottleneck for the widespread application of Ni–Zn batteries is their poor cycling stability as a result of the irreversibility of the Ni‐based cathode and dendrite formation of the Zn anode during the charging–discharging processes. Herein, a highly rechargeable, flexible, fiber‐shaped Ni–Zn battery with impressive electrochemical performance is rationally demonstrated by employing Ni–NiO heterostructured nanosheets as the cathode. Benefiting from the improved conductivity and enhanced electroactivity of the Ni–NiO heterojunction nanosheet cathode, the as‐fabricated fiber‐shaped Ni–NiO//Zn battery displays high capacity and admirable rate capability. More importantly, this Ni–NiO//Zn battery shows unprecedented cyclic durability both in aqueous (96.6% capacity retention after 10 000 cycles) and polymer (almost no capacity attenuation after 10 000 cycles at 22.2 A g^?1) electrolytes. Moreover, a peak energy density of 6.6 µWh cm^?2, together with a remarkable power density of 20.2 mW cm^?2, is achieved by the flexible quasi‐solid‐state fiber‐shaped Ni–NiO//Zn battery, outperforming most reported fiber‐shaped energy‐storage devices. Such a novel concept of a fiber‐shaped Ni–Zn battery with impressive stability will greatly enrich the flexible energy‐storage technologies for future portable/wearable electronic applications.     

Conversion Synthesis of Self‐Standing Potassium Zinc Hexacyanoferrate Arrays as Cathodes for High‐Voltage Flexible Aqueous Rechargeable Sodium‐Ion Batteries

Prussian blue analogs exhibit great promise for applications in aqueous rechargeable sodium‐ion batteries (ARSIBs) due to their unique open framework and well‐defined discharge voltage plateau. However, traditional coprecipitation methods cannot prepare self‐standing electrodes to meet the needs of wearable energy storage devices. In this work, a water bath method is reported to grow microcube‐like K₂Zn₃(Fe(CN)₆)₂·9H₂O on carbon cloth (CC) using Zn nanosheet arrays as the zinc source and reducing agent, directly serving as a self‐standing cathode. Benefiting from fast ion diffusion and high conductivity, the cathode delivers a high areal capacity of 0.76 mAh cm^?2 at 0.5 mA cm^?2 and excellent capacity retention of 57.9% as the current density increases to 20 mA cm^?2. By coupling with NaTi₂(PO₄)₃ grown on CC as an anode, a quasi‐solid‐state flexible ARSIB with a high output voltage plateau of 1.6 V is successfully assembled, exhibiting a superior areal capacity of 0.56 mAh cm^?2 and energy density of 0.92 mWh cm^?2. In particular, the device shows admirable mechanical flexibility, maintaining 90.3% of initial capacity after 3000 bending cycles. This work is anticipated to open a new avenue for the rational design of self‐standing electrodes used in high‐voltage flexible ARSIBs.     

A Garnet-Type Solid-Electrolyte-Based Molten Lithium−Molybdenum−Iron(II) Chloride Battery with Advanced Reaction Mechanism

Solid-electrolyte-based molten-metal batteries have attracted considerable attention for grid-scale energy storage. Although ZEBRA batteries are considered one of the promising candidates, they still have the potential concern of metal particle growth and ion exchange with the β”-Al₂O₃ electrolyte. Herein, a Li_6.4La₃Zr_1.4Ta_0.6O₁₂ solid-electrolyte-based molten lithium−molybdenum−iron(II) chloride battery (denoted as Li−Mo−FeCl₂) operated at temperature of 250 °C, comprising a mixture of Fe and LiCl cathode materials, a Li anode, a garnet-type Li-ion ceramic electrolyte, and Mo additive, is designed to overcome these obstacles. Different from conventional battery reaction mechanisms, this battery revolutionarily synchronizes the reversible Fe−Mo alloying−dealloying reactions with the delithiation−lithiation processes, meaning that the porous Mo framework derived from Fe−Mo alloy simultaneously suppresses the growth of pure Fe particles. By adopting a Li anode and a Li-ion ceramic electrolyte, the corrosion problem between the cathode and the solid electrolyte is overcome. With similar battery cost ($12 kWh⁻¹), the theoretical energy density of Li−Mo−FeCl₂ battery surpasses that of a Na−FeCl₂ ZEBRA battery over 25%, to 576 Wh kg⁻¹ and 2216 Wh L⁻¹, respectively. Experimental results further prove this cell has excellent cycling performance (472 mAh g_LiCl⁻¹ after 300 cycles, 50 mg active material) and strong tolerance against the overcharge−overdischarge (3−1.6 V) and freezing−thawing (25−250 °C) incidents.     

Oxygen-deficient ammonium vanadate for flexible aqueous zinc batteries with high energy density and rate capability at −30 °C

Aqueous zinc batteries (AZBs) have received significant attention owing to environmental friendliness, high energy density and inherent safety. However, lack of high-performance cathodes has become the main bottleneck of AZBs development. Here, oxygen-deficient NH₄V₄O_10−x·nH₂O (NVOH) microspheres are synthesized and used as cathodes for AZBs. The experimental test and theoretical calculations demonstrate that the oxygen vacancies in the lattice lower the Zn²⁺ diffusion energy barrier, which enables fast Zn²⁺ diffusion and good electrochemical performance in a wide temperature range. The suppressed side reactions also can help to improve the low temperature performance. NVOH shows a high energy density of 372.4 Wh kg⁻¹ and 296 Wh kg⁻¹ at room temperature and −30 °C, respectively. Moreover, NVOH maintains a 100% capacity retention after 100 cycles at 0.1 A g⁻¹ and ∼94% capacity retention after 2600 cycles at 2 A g⁻¹ and −30 °C. Investigation into the mechanism of the process reveals that the capacity contribution of surface capacitive behaviors is dominant and capacity attenuation is mainly caused by the decay of diffusion-controlled capacity. Furthermore, flexible AZBs can steadily power portable electronics under different bending states, demonstrating its great potential in wide-temperature wearable device.     

Structure-Controlled Carbon Hosts for Dendrite-Free Aqueous Zinc Batteries

The surging demand for environmental-friendly and safe electrochemical energy storage systems has driven the development of aqueous zinc (Zn)-ion batteries (ZIBs). However, metallic Zn anodes suffer from severe dendrite growth and large volume change, resulting in a limited lifetime for aqueous ZIB applications. Here, it is shown that 3D mesoporous carbon (MC) with controlled carbon and defect configurations can function as a highly reversible and dendrite-free Zn host, enabling the stable operation of aqueous ZIBs. The MC host has a structure-controlled architecture that contains optimal sp²-carbon and defect sites, which results in an improved initial nucleation energy barrier and promotes uniform Zn deposition. As a consequence, the MC host shows outstanding Zn plating/stripping performance over 1000 cycles at 2 mA cm⁻² and over 250 cycles at 6 mA cm⁻² in asymmetric cells. Density functional theory calculations further reveal the role of the defective sp²-carbon surface in Zn adsorption energy. Moreover, a full cell based on Zn@MC900 anode and V₂O₅ cathode exhibits remarkable rate performance and cycling stability over 3500 cycles. These results establish a structure-mechanism-performance relationship of the carbon host as a highly reversible Zn anode for the reliable operation of ZIBs.     

Extended Electrochemical Window of Solid Electrolytes via Heterogeneous Multilayered Structure for High‐Voltage Lithium Metal Batteries

In response to the call for safer high‐energy‐density storage systems, high‐voltage solid‐state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be stable against both Li anode and high‐voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0–5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation‐resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li_1.4Al_0.4Ge_1.6(PO₄)₃ (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi_0.6Co_0.2Mn_0.2O₂ and LiNi_0.8Co_0.1Mn_0.1O₂ cathodes, which are rarely used in solid‐state batteries, the solid‐state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm^?2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high‐voltage solid‐state Li metal batteries.     

A Metal–Organic Framework as a Multifunctional Ionic Sieve Membrane for Long-Life Aqueous Zinc–Iodide Batteries

The introduction of the redox couple of triiodide/iodide (I₃⁻/I⁻) into aqueous rechargeable zinc batteries is a promising energy-storage resource owing to its safety and cost-effectiveness. Nevertheless, the limited lifespan of zinc–iodine (Zn–I₂) batteries is currently far from satisfactory owing to the uncontrolled shuttling of triiodide and unfavorable side-reactions on the Zn anode. Herein, space-resolution Raman and micro-IR spectroscopies reveal that the Zn anode suffers from corrosion induced by both water and iodine species. Then, a metal–organic framework (MOF) is exploited as an ionic sieve membrane to simultaneously resolve these problems for Zn–I₂ batteries. The multifunctional MOF membrane, first, suppresses the shuttling of I₃⁻ and restrains related parasitic side-reaction on the Zn anode. Furthermore, by regulating the electrolyte solvation structure, the MOF channels construct a unique electrolyte structure (more aggregative ion associations than in saturated electrolyte). With the concurrent improvement on both the iodine cathode and the Zn anode, Zn–I₂ batteries achieve an ultralong lifespan (>6000 cycles), high capacity retention (84.6%), and high reversibility (Coulombic efficiency: 99.65%). This work not only systematically reveals the parasitic influence of free water and iodine species to the Zn anode, but also provides an efficient strategy to develop long-life aqueous Zn–I₂ batteries.     

Weak-Coordination Electrolyte Enabling Fast Li+ Transport in Lithium Metal Batteries at Ultra-Low Temperature

Lithium metal batteries (LMBs) are promising for next-generation high-energy-density batteries owing to the highest specific capacity and the lowest potential of Li metal anode. However, the LMBs are normally confronted with drastic capacity fading under extremely cold conditions mainly due to the freezing issue and sluggish Li⁺ desolvation process in commercial ethylene carbonate (EC)-based electrolyte at ultra-low temperature (e.g., below −30 °C). To overcome the above challenges, an anti-freezing carboxylic ester of methyl propionate (MP)-based electrolyte with weak Li⁺ coordination and low-freezing temperature (below −60 °C) is designed, and the corresponding LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode exhibits a higher discharge capacity of 84.2 mAh g⁻¹ and energy density of 195.0 Wh kg⁻¹_cathode than that of the cathode (1.6 mAh g⁻¹ and 3.9 Wh kg⁻¹_cathode) working in commercial EC-based electrolytes for NCM811‖ Li cell at −60 °C. Molecular dynamics simulation, Raman spectra, and nuclear magnetic resonance characterizations reveal that rich mobile Li⁺ and the unique solvation structure with weak Li⁺ coordination are achieved in MP-based electrolyte, which collectively facilitate the Li⁺ transference process at low temperature. This work provides fundamental insights into low-temperature electrolytes by regulating solvation structure, and offers the basic guidelines for the design of low-temperature electrolytes for LMBs.     

Joint Charge Storage for High‐Rate Aqueous Zinc–Manganese Dioxide Batteries

Aqueous rechargeable zinc–manganese dioxide batteries show great promise for large‐scale energy storage due to their use of environmentally friendly, abundant, and rechargeable Zn metal anodes and MnO₂ cathodes. In the literature various intercalation and conversion reaction mechanisms in MnO₂ have been reported, but it is not clear how these mechanisms can be simultaneously manipulated to improve the charge storage and transport properties. A systematical study to understand the charge storage mechanisms in a layered δ‐MnO₂ cathode is reported. An electrolyte‐dependent reaction mechanism in δ‐MnO₂ is identified. Nondiffusion controlled Zn²⁺ intercalation in bulky δ‐MnO₂ and control of H⁺ conversion reaction pathways over a wide C‐rate charge–discharge range facilitate high rate performance of the δ‐MnO₂ cathode without sacrificing the energy density in optimal electrolytes. The Zn‐δ‐MnO₂ system delivers a discharge capacity of 136.9 mAh g^?1 at 20 C and capacity retention of 93% over 4000 cycles with this joint charge storage mechanism. This study opens a new gateway for the design of high‐rate electrode materials by manipulating the effective redox reactions in electrode materials for rechargeable batteries.     

Carbon Foam-Supported VS2 Cathode for High-Performance Flexible Self-Healing Quasi-Solid-State Zinc-Ion Batteries

As the new generation of energy storage systems, the flexible battery can effectively broaden the application area and scope of energy storage devices. Flexibility and energy density are the two core evaluation parameters for the flexible battery. In this work, a flexible VS₂ material (VS₂@CF) is fabricated by growing the VS₂ nanosheet arrays on carbon foam (CF) using a simple hydrothermal method. Benefiting from the high electric conductivity and 3D foam structure, VS₂@CF shows an excellent rate capability (172.8 mAh g⁻¹ at 5 A g⁻¹) and cycling performance (130.2 mAh g⁻¹ at 1 A g⁻¹ after 1000 cycles) when it served as cathode material for aqueous zinc-ion batteries. More importantly, the quasi-solid-state battery VS₂@CF//Zn@CF assembled by the VS₂@CF cathode, CF-supported Zn anode, and a self-healing gel electrolyte also exhibits excellent rate capability (261.5 and 149.8 mAh g⁻¹ at 0.2 and 5 A g⁻¹, respectively) and cycle performance with a capacity of 126.6 mAh g⁻¹ after 100 cycles at 1 A g⁻¹. Moreover, the VS₂@CF//Zn@CF full cell also shows good flexible and self-healing properties, which can be charged and discharged normally under different bending angles and after being destroyed and then self-healing.     

A Novel Aqueous Asymmetric Supercapacitor based on Pyrene-4,5,9,10-Tetraone Functionalized Graphene as the Cathode and Annealed Ti3C2Tx MXene as the Anode

Asymmetric supercapacitors (ASCs), employing two dissimilar electrode materials with a large redox peak position difference as cathode and anode, have been designed to further broaden the voltage window and improve the energy density of supercapacitors. Organic molecule based electrodes can be constructed by combining redox-active organic molecules with conductive carbon-based materials such as graphene. Herein, pyrene-4,5,9,10-tetraone (PYT), a redox-active molecule with four carbonyl groups, exhibits a four-electron transfer process and can potentially deliver a high capacity. PYT is noncovalently combined with two different kinds of graphene (Graphenea [GN] and LayerOne [LO]) at different mass ratios. The PYT-functionalized GN electrode (PYT/GN 4–5) possesses a high capacity of 711 F g⁻¹ at 1 A g⁻¹ in 1 M H₂SO₄. To match with the PYT/GN 4–5 cathode, an annealed-Ti₃C₂T_x (A-Ti₃C₂T_x) MXene anode with a pseudocapacitive character is prepared by pyrolysis of pure Ti₃C₂T_x. The assembled PYT/GN 4–5//A-Ti₃C₂T_x ASC delivers an outstanding energy density of 18.4 Wh kg⁻¹ at a power density of 700 W kg⁻¹. The PYT-functionalized graphene holds great potential for high-performance energy storage devices.     

A High-Voltage,Dendrite-Free,and Durable Zn–Graphite Battery

The intrinsic advantages of metallic Zn, like high theoretical capacity (820 mAh g⁻¹), high abundance, low toxicity, and high safety have driven the recent booming development of rechargeable Zn batteries. However, the lack of high-voltage electrolyte and cathode materials restricts the cell voltage mostly to below 2 V. Moreover, dendrite formation and the poor rechargeability of the Zn anode hinder the long-term operation of Zn batteries. Here a high-voltage and durable Zn–graphite battery, which is enabled by a LiPF₆-containing hybrid electrolyte, is reported. The presence of LiPF₆ efficiently suppresses the anodic oxidation of Zn electrolyte and leads to a super-wide electrochemical stability window of 4 V (vs Zn/Zn²⁺). Both dendrite-free Zn plating/stripping and reversible dual-anion intercalation into the graphite cathode are realized in the hybrid electrolyte. The resultant Zn–graphite battery performs stably at a high voltage of 2.8 V with a record midpoint discharge voltage of 2.2 V. After 2000 cycles at a high charge–discharge rate, high capacity retention of 97.5% is achieved with ≈100% Coulombic efficiency.     

LiMgPO4-Coating-Induced Phosphate Shell and Bulk Mg-Doping Enables Stable Ultra-High-Voltage Cycling of LiCoO2 Cathode

Stable cycling of LiCoO₂ (LCO) cathode at high voltage is extremely challenging due to the notable structural instability in deeply delithiated states. Here, using the sol–gel coating method, LCO materials (LMP-LCO) are obtained with bulk Mg-doping and surface LiMgPO₄/Li₃PO₄ (LMP/LPO) coating. The experimental results suggest that the simultaneous modification in the bulk and at the surface is demonstrated to be highly effective in improving the high-voltage performance of LCO. LMP-LCO cathodes deliver 149.8 mAh g⁻¹@4.60 V and 146.1 mAh g⁻¹@4.65 V after 200 cycles at 1 C. For higher cut-off voltages, 4.70 and 4.80 V, LMP-LCO cathodes still achieve 144.9 mAh g⁻¹ after 150 cycles and 136.8 mAh g⁻¹ after 100 cycles at 1 C, respectively. Bulk Mg-dopants enhance the ionicity of Co O bond by tailoring the band centers of Co 3d and O 2p, promoting stable redox on O²⁻, and thus enhancing stable cycling at high cut-off voltages. Meanwhile, LMP/LPO surface coating suppresses detrimental surface side reactions while allowing facile Li-ion diffusion. The mechanism of high-voltage cycling stability is investigated by combining experimental characterizations and theoretical calculations. This study proposes a strategy of surface-to-bulk simultaneous modification to achieve superior structural stability at high voltages.     

BCP coatings on pure titanium plates by CD method

Ca–P coatings on pure titanium plates were precipitated in this work by a cathode deposition (CD) method and showed several differences from other reported works. The fast calcification solution (FCS) and revised simulation body fluid (R-SBF) were used as electrolytes. A significant difference in sizes of crystals and thickness of the precipitated coatings was observed between the bioactive calcium phosphate (BCP) coatings precipitated from FCS and from R-SBF. The possible reason of this difference was ascribed to that the ion concentrations of Ca²⁺ and HPO₄²⁻ and some inhibitors of Ca–P crystals growth such as Mg²⁺ and CO₃²⁻ ions and pH of electrolytes. The crystalline structure and composition of BCP coatings are of special importance to applications of the BCP coatings. The characterization has been fulfilled by the use of XRD, FTIR, SEM and TEM. The results of this study made it clear that the precipitates on the Ti plates by cathode deposition method in different electrolytes were not the hydroxyapatite (HA) but octacalcium phosphate (OCP) and some carbonate-containing amorphous calcium phosphate apatite, and a few of precipitates changed to needle-like HA after immerged in a 0.1 M NaOH solution at 60 °C for 48 h. The present study confirms that CD method is a more convenient and fast way to prepare BCP coatings on titanium implants than the reported works.     

Photochemical Reactions of Neptunium Ions in Aqueous Carbonate Solutions

Photochemical reactions of Np(VI), Np(V), and Np(IV) in aqueous solutions containing HCO₃ ^- and CO₃ ^2- anions were studied spectrophotometrically. Two parallel photoreactions, oxidation of Np(V) to Np(VI) and reduction of Np(VI) to Np(V), were revealed. The quantum efficiency of Np(VI) photoreduction in 1.95 M Na₂CO₃ is 0.003. As the pH of the solution decreases, Np(VI) photoreduction is decelerated and Np(V) photooxidation is accelerated. The photoconversion of Np(V) into Np(VI) in 1 M NaHCO₃ is 94-95%. The presence of oxygen has no effect on the oxidation. Neptunium(IV) is oxidized to Np(V) and Np(VI).     

Mesopore‐Induced Ultrafast Na+‐Storage in T‐Nb2O5/Carbon Nanofiber Films toward Flexible High‐Power Na‐Ion Capacitors

Hybrid Na‐ion capacitors (NICs) are receiving considerable interest because they combine the merits of both batteries and supercapacitors and because of the low‐cost of sodium resources. However, further large‐scale deployment of NICs is impeded by the sluggish diffusion of Na⁺ in the anode. To achieve rapid redox kinetics, herein the controlled fabrication of mesoporous orthorhombic‐Nb₂O₅ (T‐Nb₂O₅)/carbon nanofiber (CNF) networks is demonstrated via in situ SiO₂‐etching. The as‐obtained mesoporous T‐Nb₂O₅ (m‐Nb₂O₅)/CNF membranes are mechanically flexible without using any additives, binders, or current collectors. The in situ formed mesopores can efficiently increase Na⁺‐storage performances of the m‐Nb₂O₅/CNF electrode, such as excellent rate capability (up to 150 C) and outstanding cyclability (94% retention after 10 000 cycles at 100 C). A flexible NIC device based on the m‐Nb₂O₅/CNF anode and the graphene framework (GF)/mesoporous carbon nanofiber (mCNF) cathode, is further constructed, and delivers an ultrahigh power density of 60 kW kg^?1 at 55 Wh kg^?1 (based on the total weight of m‐Nb₂O₅/CNF and GF/mCNF). More importantly, owing to the free‐standing flexible electrode configuration, the m‐Nb₂O₅/CNF//GF/mCNF NIC exhibits high volumetric energy and power densities (11.2 mWh cm^?3, 5.4 W cm^?3) based on the full device, which holds great promise in a wide variety of flexible electronics.