Advanced Materials for Sodium-Ion Capacitors with Superior Energy-Power Properties: Progress and Perspectives.

Developing electrochemical energy storage devices with high energy-power densities, long cycling life, as well as low cost is of great significance. Sodium-ion capacitors (NICs), with Na+ as carriers, are composed of a high capacity battery-type electrode and a high rate capacitive electrode. However, unlike their lithium-ion analogues, the research on NICs is still in its infancy. Rational material designs still need to be developed to meet the increasing requirements for NICs with superior energy-power performance and low cost. In the past few years, various materials have been explored to develop NICs with the merits of superior electrochemical performance, low cost, good stability, and environmental friendliness. Here, the material design strategies for sodium-ion capacitors are summarized, with focus on cathode materials, anode materials, and electrolytes. The challenges and opportunities ahead for the future research on materials for NICs are also proposed.

Building Carbon-Based Versatile Scaffolds on the Electrode Surface to Boost Capacitive Performance for Fiber Pseudocapacitors.

In order to fabricate high performance fiber pseudocapacitors, the trade-off between high mass loading and high utilization efficiency of pseudocapacitive materials should be carefully addressed. Here, a solution that is to construct a carbon-based versatile scaffold is reported for loading pseudocapacitive materials on carbonaceous fibers. The scaffold can be easily built by conformally coating commercial pen ink on the fibers without any destruction to the fiber skeleton. Due to the high electrical conductivity and abundant macropore structure, it can provide sufficient loading room and a high ion/electron conductive network for pseudocapacitive materials. Therefore, their loading mass and utilization efficiency can be increased simultaneously, and thus the as-designed fibrous electrode displays a high areal capacitance of 649 mF cm-2 (or 122 mF cm-1 based on length), which is higher than most of the reported fiber pseudocapacitors. The simple and low-cost strategy opens up a new way to prepare high performance portable/wearable energy storage devices.

High Areal Capacity Li-Ion Storage of Binder-Free Metal Vanadate/Carbon Hybrid Anode by Ion-Exchange Reaction.

Storing more energy in a limited device area is very challenging but crucial for the applications of flexible and wearable electronics. Metal vanadates have been regarded as a fascinating group of materials in many areas, especially in lithium-ion storage. However, there has not been a versatile strategy to synthesize flexible metal vanadate hybrid nanostructures as binder-free anodes for Li-ion batteries so far. A convenient and versatile synthesis of Mx Vy Ox+2.5y @carbon cloth (M = Mn, Co, Ni, Cu) composites is proposed here based on a two-step hydrothermal route. As-synthesized products demonstrate hierarchical proliferous structure, ranging from nanoparticles (0D), and nanobelts (1D) to a 3D interconnected network. The metal vanadate/carbon hybrid nanostructures exhibit excellent lithium storage capability, with a high areal specific capacity up to 5.9 mAh cm-2 (which equals to 1676.8 mAh g-1 ) at a current density of 200 mA g-1 . Moreover, the nature of good flexibility, mixed valence states, and ultrahigh mass loading density (over 3.5 mg cm-2 ) all guarantee their great potential in compact energy storage for future wearable devices and other related applications.

A Composite Polymeric Carbon Nitride with In Situ Formed Isotype Heterojunctions for Highly Improved Photocatalysis under Visible Light.

Introducing heterojunction is an effective way for improving the intrinsic photocatalytic activity of a graphitic carbon nitride (GCN) semiconductor. These heterostructures are mostly introduced by interfacing GCN with foreign materials that normally have entirely different physicochemical properties and show unfavorable compatibility, thus resulting in a limited improvement of the photocatalytic performance of the resultant materials. Herein, a composite polymeric carbon nitride (CPCN) that contains both melon-based GCN and triazine-based crystalline carbon nitride (CCN) is prepared by a simple thermal reaction between lithium chloride and GCN. Thanks to the intimate contact and good compatibility between GCN and CCN, an in situ formed heterojunction acts as a driving force for separating the photogenerated charge carriers in CPCN. As a result, CPCN exhibits a significantly improved photocatalytic performance under visible light irradiation, which is, respectively, 10.6 and 5.3 times as high as those of the GCN and CCN alone. This well designed isotype heterojunction by a coupling of CCN presents an effective avenue for developing efficient GCN photocatalysts.

Amino-Modified Graphene Oxide from Kish Graphite for Enhancing Corrosion Resistance of Waterborne Epoxy Coatings.

Waterborne epoxy (WEP) coatings with enhanced corrosion resistance were prepared using graphene oxide (GO) that was obtained from kish graphite, and amino-functionalized graphene oxide (AGO) was modified by 2-aminomalonamide. The structural characteristics of the GO and AGO were analyzed using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). And the anti-corrosive performance of waterborne epoxy-cased composite coatings with different addition amounts of AGO was investigated using electrochemical measurements, pull-off adhesion tests, and salt spray tests. The results indicate that AGO15/WEP with 0.15 wt.% of AGO has the best anti-corrosive performance, and the lowest frequency impedance modulus increased from 1.03 × 108 to 1.63 × 1010 ohm·cm-2 compared to that of WEP. Furthermore, AGO15/WEP also demonstrates the minimal corrosion products or bubbles in the salt spray test for 200 h, affirming its exceptional long-term corrosion protection capability.

Adsorption removal of styrene on C-Cl grafted silica gel adsorbents.

The heat desorption of styrene from adsorbents is impracticable owing to its spontaneous polymerization under heating conditions. However, the feature also brings a potential promoting effect on styrene adsorption. Therefore, it is expected to develop the non-regenerative adsorbents with large adsorption capacity by strengthening the polymerization effect. In this work, C-Cl grafted silica gel adsorbents were prepared by introducing (Chloromethyl)dimethylchlorosilane (CMDMCS) and FeCl2 into silica gel. The C-Cl grafted silica gel exhibited excellent styrene adsorption performance, its adsorption amounts for styrene were 4.67 times and 9 times of unmodified silica gel under dry air condition and high humidity condition (RH = 80%), respectively. In addition, the adsorption of styrene on C-Cl grafted silica gel was almost unaffected by the presence of toluene. The characterization of adsorbents after styrene adsorption indicated that the improvement of adsorption capacity of C-Cl grafted silica gel for styrene can be attributed to atom transfer radical polymerization (ATRP) of styrene molecules on modified silica gel during adsorption process.

Porous nitrogen-doped reduced graphene oxide-supported CuO@Cu2O hybrid electrodes for highly sensitive enzyme-free glucose biosensor.

Constructing high-performance enzyme-free biosensors for detecting glucose is essential to preliminary diabetes diagnosis. Here, copper oxide nanoparticles (CuO@Cu2O NPs) were anchored in porous nitrogen-doped reduced graphene oxide (PNrGO) to construct CuO@Cu2O/PNrGO/GCE hybrid electrode for sensitive detection of glucose. Benefiting from the remarkable synergistic effects between the multiple high activation sites of CuO@Cu2O NPs and the dramatic properties of PNrGO with excellent conductivity and large surface area with many accessible pores, the hybrid electrode possesses outstanding glucose sensing performance that is far superior to those of pristine CuO@Cu2O electrode. The as-fabricated enzyme-free glucose biosensor displays prominent glucose sensitivity of 2,906.07 µA mM-1 cm-2, extremely low limit of detection of 0.13 µM, and wide linear detection of 3 µM-6.772 mM. In addition, excellent reproducibility, favorable long-term stability, and distinguished selectivity are obtained in the glucose detection. Importantly, this study provides promising results for continuous improvement of non-enzyme sensing applications.

Relation between the charge efficiency of activated carbon fiber and its desalination performance.

Four types of activated carbon fibers (ACFs) with different specific surface areas (SSA) were used as electrode materials for water desalination using capacitive deionization (CDI). The carbon fibers were characterized by scanning electron microscopy and N(2) adsorption at 77 K, and the CDI process was investigated by studying the salt adsorption, charge transfer, and also the charge efficiency of the electric double layers that are formed within the micropores inside the carbon electrodes. It is found that the physical adsorption capacity of NaCl by the ACFs increases with increasing Brunauer-Emmett-Teller (BET) surface area of the fibers. However, the two ACF materials with the highest BET surface area have the lowest electrosorptive capability. Experiments indicate that the charge efficiency of the double layers is a key property of the ACF-based electrodes because the ACF material which has the maximum charge efficiency also shows the highest salt adsorption capacity for CDI.

Re-understanding and focusing on normoalbuminuric diabetic kidney disease.

Diabetes mellitus (DM) has grown up to be an important issue of global public health because of its high incidence rate. About 25% of DM patients can develop diabetic foot/ulcers (DF/DFU). Diabetic kidney disease (DKD) is the main cause of end-stage kidney disease (ESKD). DF/DFU and DKD are serious complications of DM. Therefore, early diagnosis and timely prevention and treatment of DF/DFU and DKD are essential for the progress of DM. The clinical diagnosis and staging of DKD are mostly based on the urinary albumin excretion rate (UAER) and EGFR. However, clinically, DKD patients show normoalbuminuric diabetic kidney disease (NADKD) instead of clinical proteinuria. The old NADKD concept is no longer suitable and should be updated accordingly with the redefinition of normal proteinuria by NKF/FDA. Based on the relevant guidelines of DM and CKD and combined with the current situation of clinical research, the review described NADKD from the aspects of epidemiology, pathological mechanism, clinical characteristics, biomarkers, disease diagnosis, and the relationship with DF/DFU to arouse the new understanding of NADKD in the medical profession and pay attention to it.

Exfoliated graphite blocks with resilience prepared by room temperature exfoliation and their application for oil-water separation.

Exfoliated graphite (EG) blocks are prepared from the ultra-large flakes of graphite by intercalation of H2SO4 using a large amount of H2O2 at 5 °C and following exfoliation at 30 °C. By the exfoliation in a closed container, EG blocks with the bulk densities of 0.008-0.024 g/cm3 are successfully prepared. The resultant EG blocks have high sorption capacities for a diesel oil, up to 45 g/g. The EG blocks after oil sorption can get certain resilience for compressive stress with high reproducibility by compression-release cycles, which allows us to apply the compression-releasing for the oil sorption-desorption of the EG blocks. The performance of cyclic oil sorption-desorption by compression-releasing of EG block is compared with those of filtration and distillation. Since the resultant EG blocks had sufficient mechanical strength, the continuous removal of oil floating on the water surface is possible, exporting oil through a catheter inserted into the block and connected to a peristaltic pump. By warming up by Joule heating, even a crude oil having high viscosity can be continuously removed from the water with sufficient rate. The high hydrophobicity and lipophilicity of EG make selective removal of oil from water possible.

Adsorptive removal of gas phase naphthalene on ordered mesoporous carbon.

Adsorptive removal of gas phase low concentration macromolecular organic component, represented by naphthalene, from the enclosed space using ordered mesoporous carbon (OMC) has been studied by molecular simulation and experimental investigation. The simulation results indicated that both adsorption capacity and adsorption stability of the OMCs for naphthalene decreased with the increase of pore sizes from 2 nm to 8 nm. Characterizations showed that the prepared OMCs had the pore structure similar to the simulated OMCs except for the rough surface. In particular, the adsorption performance of the prepared OMCs was significantly lower than that of the simulated OMCs when pore size was 2 nm and 3 nm, which was attributed to the rough inner surface of these adsorbents, blocking the narrow pore channels and significantly reducing the pore volume. OMC with pore size of 4 nm had the highest adsorption amount for naphthalene. The co-adsorption experiments in the presence of both naphthalene and toluene, acetone or water showed the adsorption performance of OMCs for naphthalene were almost unaffected by the presence of low concentration toluene and acetone, as well as high relative humidity.

Adsorption of lead(II) ions from aqueous solution on low-temperature exfoliated graphene nanosheets.

Graphene nanosheets (GNSs) that were obtained by vacuum-promoted low-temperature exfoliation were used to adsorb lead ions from an aqueous system. The pristine and thermally modified GNSs were characterized with scanning electron microscopy observation and X-ray photoelectron spectroscopy analysis. It was interestingly found that the adsorption against lead ions was enhanced by heat treatment, although the oxygen complexes of GNSs showed a significant decrease. In addition, lead ion uptake resulted in an increase in the pH value of the solution. It is supposed that the Lewis basicity of GNSs is improved by heat treatment under a high vacuum, in favor of simultaneous adsorption of lead ions and protons onto GNSs.

Combining Multiple Methods for Recycling of Kish Graphite from Steelmaking Slags and Oil Sorption Performance of Kish-Based Expanded Graphite.

The utilization of industrial waste as renewable resources is an essential issue of sustainable development. Kish graphite is a precipitate of excess carbon generated during the cooling of molten iron and one of the byproducts associated with steel slags. The scale-up recycling of kish graphite from steelmaking slags is a promising way to develop natural graphite alternatives. However, only one means cannot work efficiently because of the unusual occurrence of associated impurities; combining multiple separation methods is the solution. In this paper, we proposed an integrated beneficiation process, pneumatic separation-flotation-sonication-magnetic separation, to recycle kish graphite flakes with a high graphitization degree and investigated the sorption performance of various oils on kish-based expanded graphite. The new process avoided shortages such as the sediments of iron particles in the flotation cell and the loss of clean graphite in the magnetic separation. Consequently, the carbon content of kish graphite reached ∼95% after separation and >99% after acid leaching. The macroscopic structural defects of kish particles created more active sites, made the intercalation of KG-GICs faster, and yielded better-staged compounds. The kish graphite-based expanded graphite presented an octopus-like shape and exhibited an expansion volume of ∼150 mL/g. Furthermore, the developed macropore structure of the obtained kish graphite-based expanded graphite led to a superior sorption performance for oils. This work supplies one feasible and promising way to recycle kish graphite from steelmaking slags and use it.

One-step green fabrication of hierarchically porous hollow carbon nanospheres (HCNSs) from raw biomass: Formation mechanisms and supercapacitor applications.

Hierarchical porous hollow carbon nanospheres (HCNSs) were fabricated directly from raw biomass via a one-step method, in which HCNSs were obtained by thermal treatment of raw biomass in the presence of polytetrafluoroethylene (PTFE). The HCNSs possess coupling merits of uniformly distributed hollow spherical architectures, and high specific surface area, abundant accessible/open micropores and reasonable mesopores, the HCNS-based electrodes deliver high electrochemical capacitance. The formation mechanisms of pores and hollow core-shell structures were explored thoroughly, it is found that the key to the formation of hollow core-shell structure is the onset-pyrolysis temperature difference between raw biomass and PTFE. Moreover, the content of silica had significant effects on the textures of HCNSs, and HCNS with the largest SSA of 1984 m2/g was obtained. Accordingly, a possible mechanism of HCNSs formation was proposed here, where PTFE acted as the pore creation and nucleation agents and raw biomasses were the primary carbon precursors.

Blow-spun N-doped carbon fiber based high performance flexible lithium ion capacitors.

Constructing flexible hybrid supercapacitors is a feasible way to achieve devices with high energy density, high power density and flexibility at the same time. Herein, flexible asymmetric hybrid supercapacitors are fabricated with blow spun activated carbon fibers. Owing to the highly effective conductive network, abundant nitrogen doping, optimized pore-structure and surface chemical properties of the carbon fibers, the as-prepared flexible hybrid supercapacitor shows outstanding energy and power performance (98 W h kg-1 (0.3 mW h cm-2) @ 400 W kg-1, 9 W h kg-1 @ 34 kW kg-1), as well as excellent cycle stability with 93% capacitance retention after 4000 cycles.

Na0.76V6O15/Activated Carbon Hybrid Cathode for High-Performance Lithium-Ion Capacitors.

Lithium-ion hybrid capacitors (LICs) are regarded as one of the most promising next generation energy storage devices. Commercial activated carbon materials with low cost and excellent cycling stability are widely used as cathode materials for LICs, however, their low energy density remains a significant challenge for the practical applications of LICs. Herein, Na0.76V6O15 nanobelts (NaVO) were prepared and combined with commercial activated carbon YP50D to form hybrid cathode materials. Credit to the synergism of its capacitive effect and diffusion-controlled faradaic effect, NaVO/C hybrid cathode displays both superior cyclability and enhanced capacity. LICs were assembled with the as-prepared NaVO/C hybrid cathode and artificial graphite anode which was pre-lithiated. Furthermore, 10-NaVO/C//AG LIC delivers a high energy density of 118.9 Wh kg-1 at a power density of 220.6 W kg-1 and retains 43.7 Wh kg-1 even at a high power density of 21,793.0 W kg-1. The LIC can also maintain long-term cycling stability with capacitance retention of approximately 70% after 5000 cycles at 1 A g-1. Accordingly, hybrid cathodes composed of commercial activated carbon and a small amount of high energy battery-type materials are expected to be a candidate for low-cost advanced LICs with both high energy density and power density.

Asymmetric Supercapacitors Based on Hierarchically Nanoporous Carbon and ZnCo2O4 From a Single Biometallic Metal-Organic Frameworks (Zn/Co-MOF).

Metal-organic framework (MOF)-derived nanoporous carbons (NPCs) and porous metal oxide nanostructures or nanocomposites have gathered considerable interest due to their potential use in supercapacitor (SCs) applications, owing to their precise control over porous architectures, pore volumes, and surface area. Bimetallic MOFs could provide rich redox reactions deriving from improved charge transfer between different metal ions, so their supercapacitor performance could be further greatly enhanced. In this study, "One-for-All" strategy is adopted to synthesize both positive and negative electrodes for hybrid asymmetric SCs (ASCs) from a single bimetallic MOF. The bimetallic Zn/Co-MOF with cuboid-like structures were synthesized by a simple method. The MOF-derived nanoporous carbons (NPC) were then obtained by post-heat treatment of the as-synthesized Zn/Co-MOF and rinsing with HCl, and bimetallic oxides (ZnCo2O4) were achieved by sintering the Zn/Co-MOF in air. The as-prepared MOF-derived NPC and bimetallic oxides were utilized as negative and positive materials to assemble hybrid ASCs with 6 M KOH as an electrolyte. Owing to the matchable voltage window and specific capacitance between the negative (NPC) and positive (ZnCo2O4), the as-assembled ASCs delivered high specific capacitance of 94.4 F/g (cell), excellent energy density of 28.6 Wh/kg at a power density of 100 W/kg, and high cycling stability of 87.2% after 5,000 charge-discharge cycles. This strategy is promising in producing high-energy-density electrode materials in supercapacitors.

Steam Selective Etching: A Strategy to Effectively Enhance the Flexibility and Suppress the Volume Change of Carbonized Paper-Supported Electrodes.

Paper-supported electrodes with high flexibility have attracted much attention in flexible Li-ion batteries. However, they are restricted by the heavy inactive paper substrate and large volume change during the lithiation-delithiation process, which will lead to low capacity and poor rate capability and cyclability. Converting the paper substrate to carbon fiber by carbonization can substantially eliminate the "dead mass", but it becomes very brittle. This study reports a water-steam selective etching strategy that successfully addresses these problems. With the help of steam etching, pores are created, and transition-metal oxides are embedded into the fiber. These effectively accommodate the volume change and enhances the kinetics of ion and electron transport. The pores release the mechanical stress from bending, ensuring the sufficient bendability of carbonized paper. Benefiting from these merits, the steam-etched samples show high flexibility and possess outstanding electrochemical performance, including ultra-high capacity and superior cycling stability with capacity retention over 100% after 1500 cycles at 2 A g-1. Furthermore, a flexible Li-ion full battery using the steam-etched Fe2O3@CNF anode and LiFePO4/steam-etched CNF cathode delivers a high capacity of 623 mAh g-1 at 100 mA g-1 and stable electrochemical performances under the bent state, holding great promise for next-generation wearable devices.

Nonpyrolyzed Fe-N Coordination-Based Iron Triazolate Framework: An Efficient and Stable Electrocatalyst for Oxygen Reduction Reaction.

Pyrolyzed base-metal-based metal-organic frameworks (MOFs) with FeNx coordination are emerging as nonprecious metal catalysts for electrochemical oxygen reduction reaction (ORR). However, surprisingly, nonpyrolyzed MOFs involving Fe-N coordination have not been explored for the ORR. This study concerns the catalytic performance of a semiconducting nonpyrolyzed iron triazolate framework (FeTa2 ) for ORR in alkaline electrolyte. The FeTa2 catalyst is studied as composites with different amounts of conductive Ketjenblack carbon (KB). The performance of these FeTa2 -x KB (x denotes the KB/FeTa2 weight ratio) composites by onset and half-wave potentials of ORR appears to be superior to most previously documented nonpyrolyzed MOFs. Characterization by elemental analysis, FTIR spectroscopy, XPS, and cyclic voltammetry suggest that N-FeIII -OH- sites at the surface of FeTa2 function as the catalytic active sites. This FeTa2 also shows very stable activity during ORR, as supported by accelerated durability test of the FeTa2 -x KB sample (20 000 cycles, ca. 90 h). The framework structure of FeTa2 remains intact during the durability test, which would help to explain its excellent catalytic durability. This would be the first study demonstrating efficient and stable ORR catalysis by a nonpyrolyzed Fe-N coordination-based MOF material.

From upcycled waste polyethylene plastic to graphene/mesoporous carbon for high-voltage supercapacitors.

We report a successful design and synthesis method for developing a graphene/mesoporous carbon (G@PE40-MC700) electrode materials from upcycled waste polyethylene (PE) plastic combined with graphene oxide (GO) and flame retardant by low-temperature carbonization at 700 °C. The G@PE40-MC700 exhibits a high surface area (1175 m2 g-1) and a considerable amount of mesopores (2.30 cm3 g-1), thus improved electrochemical performance in both symmetric and hybrid supercapacitors with wide voltage windows. The hybrid supercapacitor assembled from G@PE40-MC700 as anode and LiMn2O4 as cathode operating at 2.0 V in 0.5 M Li2SO4 was investigated. The hybrid supercapacitor delivers an energy density of 47.8 Wh kg-1 at a power density of 250 W kg-1, as well as high cycling stability of 83.8 % after 5000 cycles. Furthermore, the much higher energy density of 63.3 Wh kg-1 by using G@PE40-MC700 as electrode material was achieved in high-voltage (4.0 V) symmetric supercapacitors using 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as the electrolyte with enhanced cycling stability of 89.3% after 5000 cycles. The high capacitance and rate capability of G@PE40-MC700 can be attributed to the synergistic effect of graphene and the mesoporous carbon composites. Our work not only offers a sustainable approach to turn waste plastic into valuable carbon materials but also an opportunity for its applications in "gold capacitors."