Pseudocapacitive Behavior Research Articles

Fe-N/C anode with pseudocapacitive behavior derived from Fe-modified ZIF-8/C composites for phosphorus capture

Capacitive deionization (CDI) is a promising phosphorus (P) electrosorption technology with no secondary pollution, cost-effectiveness, energy efficiency, and easy regeneration. In this study, Fe-N/C composites have been successfully synthesized for phosphorus capture. The optimal Fe-N/C-1000 electrode presented higher electrosorption performance and low energy consumption (3.823 kWh/kg (1.447 ×10−2 kWh/m3)) for 5 mg P/L solution than Fe-N/C-900 and Fe-N/C-800 at 1.2 V, which was owed to its superior conductive network, high specific surface area, and abundant Fe-Nx sites. The diffusion-controlled process (pseudocapacitive) contributed more significantly to the electrosorption of Fe-N/C-1000 than the capacitance-controlled process. The effects of key operational factors on phosphorus uptake in the CDI process, and the corresponding kinetics and Ragone plot were also discussed in detail. The phosphorus capture mechanism was fully explicated by discussing the characterization data and experimental results. This study may provide new insight for further applications of low-cost Fe-N/C in CDI processes.

Pseudocapacitive Potassium-Ion Intercalation Enabled by Topologically Defective Soft Carbon toward High-Rate, Large-Areal-Capacity, and Low-Temperature Potassium-Ion Batteries.

Carbonaceous materials are widely investigated as anodes for potassium-ion batteries (PIBs). However, the inferior rate capability, low areal capacity, and limited working temperature caused by sluggish K-ions diffusion kinetics are still primary challenges for carbon-based anodes. Herein, a simple temperature-programmed co-pyrolysis strategy is proposed for the efficient synthesis of topologically defective soft carbon (TDSC) based on inexpensive pitch and melamine. The skeletons of TDSC are optimized with shortened graphite-like microcrystals, enlarged interlayer spacing, and abundant topological defects (e.g., pentagons, heptagons, and octagons), which endow TDSC with fast pseudocapacitive K-ion intercalation behavior. Meanwhile, micrometer-sized structure can reduce the electrolyte degradation over particle surface and avoid unnecessary voids, ensuring a high initial Coulombic efficiency as well as high energy density. These synergistic structural advantages contribute to excellent rate capability (116mAhg-1 at 20 C), impressive areal capacity (1.83mAhcm-2 with a mass loading of 8.32mg cm-2 ), long-term cycling stability (capacity retention of 91.8% after 1200h cycling), and low working temperature (-10°C) of TDSC anodes, demonstrating great potential for the practical application of PIBs.

An inexpensive preparation of unique nano-micro porous LiFePO4 cathode with excellent rate capability for lithium-ion batteries

The application of LiFePO4 cathode material in the field of power lithium-ion batteries is seriously hampered by its poor rate performance that is triggered by its inherent poor electrical conductivity and low ion diffusion coefficient. Herein, an inexpensive and facile preparation method is developed to fabricate a novel nano-micro porous structural LiFePO4 cathode using 30 nm carbon black and iron powder as direct raw materials. It is found that the added amount of carbon black is an important factor affecting the phase and morphology of the products. Optimizing the amount of carbon black, the LiFePO4 cathode with the unique nano-micro porous structure and high specific surface area could be obtained. Such unique porous architecture with a high specific surface area can accelerate lithium-ion diffusion during charge/discharge to promote its rate performance. Meanwhile, the residual graphitized carbon derived from carbon black can not only enlarge the surface pseudocapacitance under high C rates but also enhance its electronic conductivity. Benefit from the suitable pseudocapacitive behavior and high Li+ diffusion coefficient, the LFP-1.5 electrode exhibits a discharge specific capacity of 166.27 mAh/g at 0.1C and 124.95 mAh/g at 20C, indicating prominent discharge specific capacity and excellent high-rate charge/discharge capability.

Micropore-facilitated surface-dominated pseudocapacitive storage in MOF-derived hollow nano-cuboids enabled by in-situ Zn-sacrificed strategy

Herein, we report a novel metal–organic frameworks (MOF)-derived nanomaterial, this is hollow nano-cuboids composed of NiCoP particles and nanocarbon, which is enriched in appropriate micropores induced by in-situ Zn-sacrificed strategy (NiCoP@C(Zn)). Such abundant micropores (∼0.5 nm, larger than the radius of OH−) can supply more ion shuttle channels at multi-directions, greatly-reducing the longitudinal migration time in the hollow structure, resulting in a rather high ion diffusion coefficient (∼10−8 cm2 s−1). This combined with hollow topology show the marked electrolyte-accessibility recognized by experimental and density functional theory (DFT) results, which can adequately-expose the electrochemically active sites, thus birthing a surface-dominated pseudocapacitive behaviors towards high-rate response and high-capacity storage. Due to the robust structural merits and pore character as well as their synergy, the NiCoP@C(Zn) electrode can realize a rather stable cyclability (over 10,000 cycles). Further, we construct the pouch-type supercapacitor based on NiCoP@C(Zn) cathode, which delivers a relatively-good energy output (35.2 Wh kg−1), superior to those of some previously-reported asymmetric supercapacitors. Remarkably, such pouch device can exhibit the triple-high properties, including high mechanical reliability, high safety and high availability in real-word application. This work successfully-discloses the influence of well-matched micropores on pseudocapacitive charge storage, and opens new horizons of developing a high-performance electrode nanomaterial.

Facile synthesis of N-doped reduced graphene oxide matrix-covered porous Fe2VO4 hybrid composite nanostructures as anode material for lithium-ion batteries

For iron vanadium-based lithium (Li)-ion batteries (LIBs), enhancing solidity as well as exploring storage mechanism is important. Herein, a facile hydrothermal method is employed to fabricate N-doped reduced graphene oxide-wrapped porous iron vanadate (FVO@N-rGO) hybrid composite nanostructures (HCNSs), followed by the calcination under the N2 atmosphere. The as-prepared FVO@N-rGO HCNSs are used as an anode material for LIBs. The FVO@N-rGO HCNSs electrode delivers a high reversible specific capacity of 711 mA h g−1 at 100 mA g−1 and durable cycling life (226 mA h g−1 at 3000 mA g−1). The Li+ intercalation kinetics (from cyclic voltammetry analysis) reveal that the Li storage capacity of FVO@N-rGO HCNSs is normally dominated via a pseudo-capacitive behavior. A full cell using commercial LiNi0.3Mn0.3Co0.3O2 (NMC111) as a cathode and pristine FVO nanospheres and FVO@N-rGO HCNSs as an anode is also fabricated. The obtained good reversible capacity, stability, and rate capability may be due to the synergetic result of three-dimensional HCNSs construction and porous morphology with a large surface area, which offers void space to shield size expansion/contraction along with reducing the diffusion coefficient for Li ions/electrons in the cycling process. Thus, this study gives a deep understanding of improving the cell performance of iron vanadium-based LIBs.

Mechanochemical Pretreated Mn+1AXn (MAX) Phase to Synthesize 2D-Ti3C2Tx MXene Sheets for High-Performance Supercapacitors.

Two-dimensional (2D) MXenes sheet-like micro-structures have attracted attention as an effective electrochemical energy storage material due to their efficient electrolyte/cation interfacial charge transports inside the 2D sheets which results in ultrahigh rate capability and high volumetric capacitance. In this article, Ti3C2Tx MXene is prepared by a combination of ball milling and chemical etching from Ti3AlC2 powder. The effects of ball milling and etching duration on the physiochemical properties are also explored, as well as the electrochemical performance of as-prepared Ti3C2 MXene. The electrochemical performances of 6 h mechanochemically treated and 12 h chemically etched MXene (BM-12H) exhibit an electric double layer capacitance behavior with an enhanced specific capacitance of 146.3 F g-1 compared to 24 and 48 h treated samples. Moreover, 5000-cycle stability tested sample's (BM-12H) charge/discharge show increased specific capacitance due to the termination of the -OH group, intercalation of K+ ion and transformation to TiO2/Ti3C2 hybrid structure in a 3 M KOH electrolyte. Interestingly, a symmetric supercapacitor (SSC) device fabricated in a 1 M LiPF6 electrolyte in order to extend the voltage window up to 3 V shows a pseudocapacitance behavior due to Li on interaction/de-intercalation. In addition, the SSC shows an excellent energy and power density of 138.33 W h kg-1 and 1500 W kg-1, respectively. The ball milling pre-treated MXene exhibited an excellent performance and stability due to the increased interlayer distance between the MXene sheets and intercalation and deintercalation of Li+ ions.

Bifunctional electrode of bismuth tungsten for electrochemical sensing applications

A co-precipitation technique has been used to prepare Bismuth tungstate nanoparticles (Bi2WO6) for electrochemical capacitors and electrochemical sensing of Ascorbic acid (AA). Using a scanning rate of 10 mV s −1, the electrode was performed as the pseudocapacitance behavior and the specific capacitance to be up to 677 Fg −1 at 1 A/g. Bi2WO6 versus Glassy carbon electrode (GCE) was also used to study the behavior of the Bi2WO6 modified electrodes in detecting ascorbic acid. This electrochemical sensor shows excellent electrocatalytic performance when ascorbic acid is present, as determined by differential pulse voltammetry. In solution, ascorbic acid diffuses to an electrode surface and controls its surface properties. Based on the results from the investigation, the sensor showed a detection sensitivity of 0.26 mM/mA, and a limit of detection (LOD) of 77.85 mM. It is clear from these results that Bi2WO6 may find application as an electrode material for supercapacitors and glucose sensors.

Pseudocapacitive behaviors of strontium-doped cobalt ferrite nanoparticles for supercapacitor applications

Metal oxides are widely used as electrode materials due to their high potential for various applications. Specifically, spinel-structured cobalt ferrite is employed in various energy applications. Among the available conventional techniques to synthesize nano-ferrites, the sol-gel combustion approach is one of the simplest and most effective. In this work, strontium-doped cobalt ferrite nanoparticles are synthesized using the sol-gel combustion technique and annealed at various temperatures. Further, the prepared samples are characterized using XRD to identify the phase and crystallinity of the materials. It shows the average crystallite sizes of 33, 36, and 35 nm for various temperatures of 200 °C, 300 °C, and 500 °C, respectively. FESEM illustrated the clustered and homogeneous structure of the sample. From UV-Vis-NIR absorption spectroscopy, direct bandgap energy values are calculated using Tauc’s plot as 1.24, 1.21, and 1.20 eV. To examine electrochemical properties, galvanostatic measurements are used. The observed sample (Co0.8Sr0.2Fe2O4 at 300 °C) shows a supercapacitance value of 637 Fg−1 at 0.5 Ag−1 and retained 85.5 % after 1000 cycles at 5 Ag−1, showing 98.79 % coulombic efficiency after 5000 cycles at 15 Ag−1. The result indicates that doped nanoferrites are a promising electrode material for supercapacitor applications.

Introducing Hybrid Defects of Silicon Doping and Oxygen Vacancies into MOF-Derived TiO2-X @Carbon Nanotablets Toward High-Performance Sodium-Ion Storage.

Titanium dioxide (TiO2 ) is a promising anode material for sodium-ion batteries (SIBs), which suffer from the intrinsic sluggish ion transferability and poor conductivity. To overcome these drawbacks, a facile strategy is developed to synergistically engineer the lattice defects (i.e., heteroatom doping and oxygen vacancy generation) and the fine microstructure (i.e., carbon hybridization and porous structure) of TiO2 -based anode, which efficiently enhances the sodium storage performance. Herein, it is successfully realized that the Si-doping into the MIL-125 metal-organic framework structure, which can be easily converted to SiO2 /TiO2-x @C nanotablets by annealing under inert atmosphere. After NaOH etching SiO2 /TiO2-x @C which contains unbonded SiO2 and chemically bonded SiOTi, thus the lattice Si-doped TiO2-x @C (Si-TiO2-x @C) nanotablets with rich Ti3+ /oxygen vacancies and abundant inner pores are developed. When examined as an anode for SIB, the Si-TiO2-x @C exhibits a high sodium storage capacity (285mAhg-1 at 0.2Ag-1 ), excellent long-term cycling, and high-rate performances (190mAhg-1 at 2Ag-1 after 2500 cycles with 95.1% capacity retention). Theoretical calculations indicate that the rich Ti3+ /oxygen vacancies and Si-doping synergistically contribute to a narrowed bandgap and lower sodiation barrier, which thus lead to fast electron/ion transfer coefficients and the predominant pseudocapacitive sodium storage behavior.

Biowaste-derived oxygen-self-doped three-dimensional interconnected porous carbon for electrochemical supercapacitor applications

ABSTRACT Biowaste for producing a biomaterial is an inexpensive, profuse, widely available, and viable natural source and has been extensively investigated and applied in a wide range of research fields. In this work, jackfruit leaf waste as a biowaste source was utilized to prepare a three-dimensional (3D) interconnected porous carbon framework self-doped with oxygen by KOH impregnation, carbonization, and activation under a CO2 atmosphere. The as-prepared porous carbon has a 3D interconnected porous framework with a rich oxygen content of 36.82%, and high BET surface area of 455.687 m2 g−1 with a pore volume of 0.522 cm3 g−1. The 3D interconnected porous framework exhibits a high specific capacitance of 199 F g−1 with a maximum energy density of 27.64 Wh kg−1 at a power density of 99.60 W kg−1 at a sweep rate of 1 mV s−1 in a two-electrode setup. The correlation between structure and great performance of electrode materials is deeply studied. The great capacitive performance of porous carbon materials can be assigned to its 3D interconnected porous framework, high specific surface area, suitable pore size distributions, and advantageous heteroatom-doping, resulting in the rapid ion diffusion and sufficient charge storage along with the contributed pseudocapacitance behavior. Hence, the exciting results reveal an efficient, cost-effective, time-saving, and facile method to prepare 3D interconnected porous carbon frameworks self-doped with oxygen derived from natural biowaste sources for developing supercapacitor devices.

Dimensionality effects of g-C3N4 from wettability to solar light assisted self-cleaning and electrocatalytic oxygen evolution reaction

Unique interfacial properties of 2D materials make them more functional than their bulk counterparts in a catalytic application. In the present study, bulk and 2D graphitic carbon nitride nanosheet (bulk g-C3N4 and 2D-g-C3N4 NS) coated cotton fabrics and nickel foam electrode interfaces have been applied for solar light-driven self-cleaning of methyl orange (MO) dye and electrocatalytic oxygen evolution reaction (OER), respectively. Compared to bulk, 2D-g-C3N4 coated interfaces show higher surface roughness (1.094 > 0.803) and enhanced hydrophilicity (θ ∼ 32° < 62° for cotton fabric and θ ∼ 25° < 54° for Ni foam substrate) due to oxygen defect induction as confirmed from morphological (HR-TEM and AFM) and interfacial (XPS) characterizations. The self-remediation efficiencies for blank and bulk/2D-g-C3N4 coated cotton fabrics are estimated through colorimetric absorbance and average intensity changes. The self-cleaning efficiency for 2D-g-C3N4 NS coated cotton fabric is 87%, whereas the blank and bulk-coated fabric show 31% and 52% efficiency. Liquid Chromatography-Mass Spectrometry (LC-MS) analysis determines the reaction intermediates for MO cleaning. 2D-g-C3N4 shows lower overpotential (108 mV) and onset potential (1.30 V) vs. RHE for 10 mA cm−2 OER current density in 0.1 M KOH. Also, the decreased charge transfer resistance (RCT = 12 Ω) and lower Tafel's slope (24 mV dec−1) of 2D-g-C3N4 make it the most efficient OER catalyst over bulk-g-C3N4 and state-of-the-art material RuO2. The pseudocapacitance behavior of OER governs the kinetics of electrode-electrolyte interaction through the electrical double layer (EDL) mechanism. The 2D electrocatalyst demonstrates long-term stability (retention ∼94%) and efficacy compared to commercial electrocatalysts.

Submerged Photosynthesis of Molybdenum–Tungsten Nanostructures for Supercapacitor Application

Research on electrochemical energy storage devices aims to produce supercapacitors via a facile and nonpolluting method. Because of unnecessary elemental doping and disordered morphologies of nano-oxides, impurities in raw materials during the conventional fabrication process would reduce the pseudocapacitance. Herein, we propose a submerged photosynthesis crystalline method for synthesizing oxygen vacancy (Vo)-enriched Mo–W oxide hydrates and Mo-doped tungsten oxide hydrate nanocomposites at 55 °C and normal pressure. In addition, this study describes the impact of Vos on pseudocapacitance using ab initio calculations based on density functional theory. Doping the WO3·0.33H2O lattice with Mo and Vos brings the conduction band closer to the Fermi energy level. The comparison of the ultraviolet–visible–near-infrared (UV–vis–NIR) irradiation spectrum and absorption coefficient calculation suggests that Mo and Vo doping is responsible for the NIR absorption. This study concludes that enriched Vos result in the highest specific capacitance and pseudocapacitive behavior of MoxW1–xO3·0.33H2O.

Pseudocapacitive charge storage behavior of cation-doped WS2 nanosheets electrode

Nanostructured two-dimensional layered semiconductors MX2 (M = Mo, W, and X = S, Se, Te) are potential candidates for electrochemical energy conversion and storage applications. Recently, different research strategies, including phase and heterostructure engineering, surface modification, and chemical doping have been employed with the aim to obtain high energy density MX2 supercapacitor electrodes. Here, we report the electrochemical supercapacitor performance of cation, Co, Ir, and Ru, doped WS2 nanosheets electrode in 1 M Na2SO4 and 2 M H2SO4 aqueous electrolyte. The structure of WS2 nanosheets is stabilized in the 2H hexagonal phase and the interlayer separation expanded after cation doping. The cation-doped WS2 nanosheet electrodes exhibit pseudocapacitive behavior with improved performance in both electrolytes. Among all, the best electrode, Ru doped WS2 nanosheets shows excellent energy storage capacity and attains a specific capacity of 438 Fg−1 in 2 M H2SO4 electrolyte. The analysis reveals that cation doping is one possible research strategy to improve the supercapacitor performance of WS2 nanosheets.

Hierarchical CoSe2/TiN/nitrogen-doped carbon nanofibers wrapped with carbon nanotubes: A binder-free anode for enhanced sodium-ion storage

Transition metal chalcogenide anodes have attracted significant attention for sodium-ion batteries (SIBs) owing to their relatively high theoretical capacity. However, the inherently poor electronic conductivity and rate performance hinder their practical application. In this study, hierarchically structured CoSe2/TiN/nitrogen-doped carbon nanofibers wrapped with in-situ grown carbon nanotubes (CNTs) on the surface (denoted as CoSe2@N-TCF/CNTs) are designed and fabricated as binder-free anodes for SIBs. The rational design can effectively avoid the agglomeration of CoSe2 nanoparticles, improve the conductivity of the composite materials, provide enough space for electrolyte penetration and volume expansion during the cycling process and shorten the transmission paths of electrons and Na+. With these structural and compositional advantages, the as-obtained hierarchical CoSe2@N-TCF/CNTs deliver a high reversible capacity of 401.2 mAh g−1 after 1000 cycles at 0.2 A g−1 and maintained at 353.7 mAh g−1 even at a high current density of 2 A g−1 when directly used as a binder-free anode for SIBs. The superior sodium-ion storage performance can be attributed to the decreased charge transfer resistance, improved Na+ diffusion rate and the pseudocapacitance behavior, as is evidenced by kinetics analysis.

Effect of a Zr-Based Metal-Organic Framework Structure on the Properties of Its Composite with Polyaniline.

Composites of polyaniline (PANI) and Zr-based metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were synthesized by the oxidative polymerization of aniline in the presence of MOF templates with the MOF content in the resulting materials (78.2 and 86.7 wt %, respectively) close to the theoretical value (91.5 wt %). Scanning electron microscopy and transmission electron microscopy showed that the morphology of the composites was set by the morphology of the MOFs, whose structure was mostly preserved after the synthesis, based on the X-ray diffraction data. Vibrational and NMR spectroscopies pointed out that MOFs participate in the protonation of PANI and conducting polymer chains were grafted to amino groups of UiO-66-NH2. Unlike PANI-UiO-66, cyclic voltammograms of PANI-UiO-66-NH2 showed a well-resolved redox peak at around ≈0 V, pointing at the pseudocapacitive behavior. The gravimetric capacitance of PANI-UiO-66-NH2, normalized per mass of the active material, was also found to be higher compared to that of pristine PANI (79.8 and 50.5 F g-1, respectively, at 5 mV s-1). The introduction of MOFs into the composites with PANI significantly improved the cycling stability of the materials over 1000 cycles compared to the pristine conducting polymer, with the residual gravimetric capacitance being ≥100 and 77%, respectively. Thus, the electrochemical performance of the prepared PANI-MOF composites makes them attractive materials for application in energy storage.

High-Performance Layered CaV4O9-MXene Composite Cathodes for Aqueous Zinc Ion Batteries.

Due to their reliability, affordability and high safety, rechargeable aqueous zinc ion batteries (ZIBs) have garnered a lot of attention. Nevertheless, undesirable long-term cycle performance and the inadequate energy density of cathode materials impede the development of ZIBs. Herein, we report a layered CaV4O9-MXene (Ti3C2Tx) composite assembled using CaV4O9 nanosheets on Ti3C2Tx and investigate its electrochemical performance as a new cathode for ZIBs, where CaV4O9 nanosheets attached on the surface of MXene and interlamination create a layered 2D structure, efficiently improving the electrical conductivity of CaV4O9 and avoiding the stacking of MXene nanosheets. The structure also enables fast ion and electron transport. Further discussion is conducted on the effects of adding MXene in various amounts on the morphology and electrochemical properties. The composite shows an improved reversible capacity of 274.3 mA h g-1 at 0.1 A g-1, superior rate capabilities at 7 A g-1, and a high specific capacity of 107.6 mA h g-1 can be delivered after 2000 cycles at a current density of 1 A g-1. The improvement of the electrochemical performance is due to its unique layered structure, high electrical conductivity, and pseudo capacitance behavior.

Boosted brackish water desalination and water softening by facilely designed MnO2/hierarchical porous carbon as capacitive deionization electrode

Capacitive deionization (CDI) is a promising technique for brackish water desalination. However, its salt electrosorption capacity is insufficient for practical application yet, and little information is available on hardness ion (Mg2+, Ca2+) removal in CDI. Herein, hierarchical porous carbon (HPC) was prepared from low-cost and renewable microalgae via a simple one-pot approach, and both MnO2/HPC and polyaniline/HPC (PANI/HPC) composites were then synthesized using a facile, one-step hydrothermal method. Compared with the MnO2 electrode, the MnO2/HPC electrode presented an improved hydrophilicity, higher specific capacitance, and lower electrode resistance. The electrodes exhibited pseudocapacitive behaviors, and the maximum salt electrosorption capacities of MnO2/HPC-PANI/HPC CDI cell was up to 0.65 mmol g−1 NaCl, 0.71 mmol g−1 MgCl2, and 0.76 mmol g−1 CaCl2, respectively, which were comparable and even higher than those of the previously reported CDI cells. Additionally, the MnO2/HPC electrode presented a selectivity order of Ca2+ ≥ Mg2+ > Na+, and the divalent cation selectivity was found to be attributed to their stronger binding strength in the cavity of MnO2. Multiscale simulations further reveal that the MnO2/HPC electrodes with the unique luminal configuration of MnO2 and HPC as supportive framework could offer a great intercalation selectivity of the divalent cations and exhibit a great promise in hardness ion removal.

Internal interface engineering of yolk-shell structure toward fast and robust potassium storage

Advanced anode materials with stable and fast K-ion storage behavior are of great significance for potassium-ion batteries (PIBs) toward large-scale applications, while it still remains a big challenging due to their intrinsic poor conductivity and large volume variation during cycles. Herein, we develop an internal interfacial engineering by encapsulating core-shell NiS2@C nanoparticles within MOF-derived hollow carbon shell for superior PIB anodes. As-prepared yolk-shell NiS2@C@C composite integrates the structure superiority of abundant interior void space, outer protective carbon shell and internal conductive carbon layer. Comprehensive experimental and theoretical methods illuminate that internal NiS2/C interface is conductive to boost charge transport kinetics, enhance pseudocapacitive behavior, and mitigate mechanical stress in outer carbon shell. As a result, it manifests an ultrahigh capacity of 481 mA h g−1 at 0.2 A g−1, and guarantees the rate capability of 306 mA h g−1 at 20 A g−1. Moreover, it presents excellent cycle stability (358 mA h g−1 after 1600 cycles at 1 A g−1), which is extremely competitive among the best reported conversion anodes for PIBs.

Lithium Niobate for Fast Cycling in Li-ion Batteries: Review and New Experimental Results

Li-Nb-O-based insertion layers between electrodes and electrolytes of Li-ion batteries (LIBs) are known to protect the electrodes and electrolytes from unwanted reactions and to enhance Li transport across interfaces. An improved operation of LIBs, including all-solid-state LIBs, is reached with Li-Nb-O-based insertion layers. This work reviews the suitability of polymorphic Li-Nb-O-based compounds (e.g., crystalline, amorphous, and mesoporous bulk materials and films produced by various methodologies) for LIB operation. The literature survey on the benefits of niobium-oxide-based materials for LIBs, and additional experimental results obtained from neutron scattering and electrochemical experiments on amorphous LiNbO3 films are the focus of the present work. Neutron reflectometry reveals a higher porosity in ion-beam sputtered amorphous LiNbO3 films (22% free volume) than in other metal oxide films such as amorphous LiAlO2 (8% free volume). The higher porosity explains the higher Li diffusivity reported in the literature for amorphous LiNbO3 films compared to other similar Li-metal oxides. The higher porosity is interpreted to be the reason for the better suitability of LiNbO3 compared to other metal oxides for improved LIB operation. New results are presented on gravimetric and volumetric capacity, potential-resolved Li+ uptake and release, pseudo-capacitive fractions, and Li diffusivities determined electrochemically during long-term cycling of LiNbO3 film electrodes with thicknesses between 14 and 150 nm. The films allow long-term cycling even for fast cycling with rates of 240C possessing reversible capacities as high as 600 mAhg−1. Electrochemical impedance spectroscopy (EIS) shows that the film atomic network is stable during cycling. The Li diffusivity estimated from the rate capability experiments is considerably lower than that obtained by EIS but coincides with that from secondary ion mass spectrometry. The mostly pseudo-capacitive behavior of the LiNbO3 films explains their ability of fast cycling. The results anticipate that amorphous LiNbO3 layers also contribute to the capacity of positive (LiNixMnyCozO2, NMC) and negative LIB electrode materials such as carbon and silicon. As an outlook, in addition to surface-engineering, the bulk-engineering of LIB electrodes may be possible with amorphous and porous LiNbO3 for fast cycling with high reversible capacity.

Three-dimensional (3D) MnMoO4@g-C3N4/CNT hybrid composite electrode for hybrid capacitive deionization

In this work, a hierarchical three-dimensional MnMoO4@g-C3N4/CNT hybrid ternary composite was developed through the facile hydrothermal method. MnMoO4@g-C3N4/CNT and g-C3N4/CNT electrodes were used as cathode and anode to fabricate the hybrid capacitive deionization (HCDI) system. Manganese molybdate (MnMoO4) rods are uniformly intertwined on the three-dimensional (3D) conductive network structure of graphitic carbon nitride/carbon nanotube (g-C3N4/CNT) heterojunction in the ternary composite. As-obtained electrode materials of MnMoO4@g-C3N4/CNT and g-C3N4/CNT show the specific capacitance of 252.4 and 89.2 Fg−1, respectively, at 1 Ag−1 in 1 M NaCl solution. Mn element in the MnMoO4@g-C3N4/CNT hybrid induces a reversible redox reaction that selectively intercalates/de-intercalates the Na+-ion in the salt solution, yielding a high salt adsorption capacity of 43.6 mg. g−1 at 1.2 V and 1000 ppm NaCl solution medium. In addition, MnMoO4@g-C3N4/CNT //g-C3N4/CNT-based HCDI cell was recycled for 10 cycles. The system reaches the highest SAC of 42.6 mg. g−1 after 10 consecutive charge–discharge cycles with a retention of 91%, indicating the excellent cycling stability of the MnMoO4@g-C3N4/CNT electrode. These results signify that the MnMoO4@g-C3N4/CNT is a promising electrode material, possessing a pseudocapacitive behavior and remarkable desalination ability, which can be a potential new candidate for the HCDI system.