Rational Synthesis of Spongy Fe3N@N-Doped Carbon Nanorods with Controlled Topography and Porosity for Enhanced Energy Storage Anodes in Lithium-Ion Batteries

Iron nitrides with the merits of high theoretical capacities, cost-effectiveness, and good electronic/ionic conductivity have been recognized as attractive anode candidates for lithium-ion batteries (LIBs). Carbon compositing, pore engineering, and nanostructure construction have proved to be effective strategies to prepare high-performance metal nitride anodes for LIBs. Herein, we synthesized a series of Fe3N-embedded and N-doped carbon nanorods (Fe3N@NCNR) with a hierarchical porous system and controllable topography by metal-catalyzed graphitization-nitridization of the Fe(III)-triazole framework (Fe-MOF) and thermal evaporation of the triblock copolymer F127 template assembled in Fe-MOF via hydrogen bonding interaction, followed by the air oxidation and urea-assisted ammonolysis processes. The Fe3N@NCNR as anodes for LIBs display extraordinary lithium storage capabilities with a high reversible capacity of 830 mA h g-1 at 0.1 C, a good rate performance of 576 mAh g-1 at 5 C, and a long-term cycling stability of 742 mA h g-1 over 600 cycles at 1 C. Such outstanding performance benefits from the spongy carbon nanorods with rich macropores for rapid electronic/ionic transport and effective accommodation of electrode volume expansion, abundant N-doped meso-/microporous carbon for the additional storage of Li+ via capacitive effect, and the efficient utilization of Fe3N nanoparticles uniformly distributed through carbon nanorods. Importantly, this work introduces an effective strategy to construct superior performance nitride anodes from MOF surfactants based on hydrogen bonding-driven interface self-assembly and provides insight into the preparation of highly efficient nanoarchitectures for Li+ storage.

Controllable Preparation of a N-Doped Hierarchical Porous Carbon Framework Derived from ZIF-8 for Highly Efficient Capacitive Deionization

Capacitive deionization (CDI) is a promising desalination technology, and metal-organic framework (MOF)-derived carbon as an electrode material has received more and more attention due to its designable structure. However, MOF-derived carbon materials with single-pore structures have been difficult to meet the technical needs of related fields. In this work, the ordered hierarchical porous carbon framework (OMCF) was prepared by the template method using zeolitic imidazolate frameworks-8 (ZIF-8) as a precursor. The pore structures, surface properties, electrochemical properties, and CDI performances of the OMCF were investigated and compared with the microporous carbon framework (MCF), also derived from ZIF-8. The results show that the hierarchical porous carbon OMCF possessed a higher specific surface area, better hydrophilic surface (with a contact angle of 13.45°), and higher specific capacitance and ion diffusion rate than those of the MCF, which made the OMCF exhibit excellent CDI performances. The adsorption capacity and salt adsorption rate of the OMCF in a 500 mg·L-1 NaCl solution at 1.2 V and a 20 mL·min-1 flow rate were 12.17 mg·g-1 and 3.34 mg·g-1·min-1, respectively, higher than those of the MCF. The deionization processes of the OMCF and MCF closely follow the pseudo-first-order kinetics, indicating the double-layer capacitance control. This work serves as a valuable reference for the CDI application of N-doped hierarchical porous carbon derived from MOFs.

Tailored Properties of Carbon for Supercapacitors by Blending Lignin and Cellulose to Mimic Biomass as Carbonaceous Precursor

KOH-activated carbon materials prepared from biomass-derived carbon source, cellulose and lignin, were compared. Mixtures of different ratios of cellulose and lignin were used to partially mimic biomass as carbon source. This allows tailoring and optimizing of the KOH activated carbon materials by getting rid of the restriction of the intrinsic proportion of cellulose and lignin in specific biomass. The results indicate that cellulose use results in a more porous structure, whereas lignin use leads to more partially activated graphite structure. The activated carbon material (CL1) prepared from blend of cellulose with lignin in mass ratio of 1 : 1 exhibits a high specific surface area of 2000.39 m2  g-1 , and in TEABF4 /ACN (tetraethylammonium tetrafluoroborate dissolved in acetonitrile) electrolyte it showed a maximum specific capacitance of 136.10 F g-1 , a maximum energy density of 18.11 Wh kg-1 , and a capacitance retention of 85.04 % under current density as high as 15 A g-1 .

Pyridinic Nitrogen Doped Carbon Dots Supply Electrons to Improve Photosynthesis and Extracellular Electron Transfer of Chlorella pyrenoidosa

Optimizing photosynthesis is imperative for providing energy and organics for all life on the earth. Here, carbon dots doped with pyridinic nitrogen (named lev-CDs) are synthesized by the one-pot hydrothermal method, and the structure-function relationship between functional groups on lev-CDs and photosynthesis of Chlorella pyrenoidosa (C. pyrenoidosa) is proposed. Pyridinic nitrogen plays a key role in the positive effect on photosynthesis caused by lev-CDs. In detail, lev-CDs act as electron donors to supply photo-induced electrons to P680⁺ and QA⁺ , causing electron transfer from lev-CDs to the photosynthetic electron transport chain in the photosystems. In return, the recombination efficiency of electron-hole pairs on lev-CDs decreases. As a result, the electron transfer rate in the electron transport chain, the activity of photosystem II, and the Calvin cycle are enhanced. Moreover, the electron transfer rate between C. pyrenoidosa and external circumstances enhanced by lev-CDs is about 50%, and electrons exported from C. pyrenoidosa can be used to reduce iron(III). This study is of great significance for engineering nanomaterials to improve photosynthesis.

Nanoporous Hollow Carbon Spheres Derived from Fullerene Assembly as Electrode Materials for High-Performance Supercapacitors

The energy storage performances of supercapacitors are expected to be enhanced by the use of nanostructured hierarchically micro/mesoporous hollow carbon materials based on their ultra-high specific surface areas and rapid diffusion of electrolyte ions through the interconnected channels of their mesoporous structures. In this work, we report the electrochemical supercapacitance properties of hollow carbon spheres prepared by high-temperature carbonization of self-assembled fullerene-ethylenediamine hollow spheres (FE-HS). FE-HS, having an average external diameter of 290 nm, an internal diameter of 65 nm, and a wall thickness of 225 nm, were prepared by using the dynamic liquid-liquid interfacial precipitation (DLLIP) method at ambient conditions of temperature and pressure. High temperature carbonization (at 700, 900, and 1100 °C) of the FE-HS yielded nanoporous (micro/mesoporous) hollow carbon spheres with large surface areas (612 to 1616 m² g^-1) and large pore volumes (0.925 to 1.346 cm³ g^-1) dependent on the temperature applied. The sample obtained by carbonization of FE-HS at 900 °C (FE-HS_900) displayed optimum surface area and exhibited remarkable electrochemical electrical double-layer capacitance properties in aq. 1 M sulfuric acid due to its well-developed porosity, interconnected pore structure, and large surface area. For a three-electrode cell setup, a specific capacitance of 293 F g^-1 at a 1 A g^-1 current density, which is approximately 4 times greater than the specific capacitance of the starting material, FE-HS. The symmetric supercapacitor cell was assembled using FE-HS_900 and attained 164 F g^-1 at 1 A g^-1 with sustained 50% capacitance at 10 A g^-1 accompanied by 96% cycle life and 98% coulombic efficiency after 10,000 consecutive charge/discharge cycles. The results demonstrate the excellent potential of these fullerene assemblies in the fabrication of nanoporous carbon materials with the extensive surface areas required for high-performance energy storage supercapacitor applications.

Evaluation of Biological Pretreatment of Wormwood Rod Reies with White Rot Fungi for Preparation of Porous Carbon

In this work, the wormwood rod residues are pretreated with white rot fungi as the precursor to preparing porous carbon following a simple carbonization and activation process (denoted herein as FWRA sample). The FWRA sample possesses abundant hierarchical pores structure with high specific surface area (1165.7 m² g^-1) and large pore volume (1.02 cm³ g^-1). As an electrode for supercapacitors, the FWRA sample offers a high specific capacitance of 443.2 F g^-1 at 0.5 A g^-1 and superb rate ability holding a specific capacitance of 270 F g^-1 at 100 A g^-1 in 6 M KOH electrolyte. The corresponding symmetrical capacitor has a superb cyclic stability with a low specific capacitance decay rate of 0.4% after 20,000 cycles at 5 A g^-1 in 1 M Na₂SO₄ electrolyte. Moreover, measurements revealed that when used as adsorbent, the FWRA sample is ideal for removing methyl orange (MO) from water, exhibiting a superior adsorption ability of 260.8 mg g^-1. Therefore, this study is expected to provide a simple and environmentally friendly technique for the generation of value-added and functional porous carbon materials from Chinese medicinal herbal residues, thus offering promising candidates for broad application areas.

Conversion of Plastic Waste to Carbon-Based Compounds and Application in Energy Storage Devices

At present, plastic waste accumulation has been observed as one of the most alarming environmental challenges, affecting all forms of life, economy, and natural ecosystems, worldwide. The overproduction of plastic materials is mainly due to human population explosion as well as extraordinary proliferation in the global economy accompanied by global productivity. Under this threat, the development of benign and green alternative solutions instead of traditional disposal methods such as conversion of plastic waste materials into cherished carbonaceous nanomaterials such as carbon nanotubes (CNTs), carbon quantum dots (CQDs), graphene, activated carbon, and porous carbon is of utmost importance. This critical review thoroughly summarizes the different types of daily used plastics, their types, properties, ways of accumulation and their effect on the environment and human health, treatment of waste materials, conversion of waste materials into carbon-based compounds through different synthetic schemes, and their utilization in energy storage devices particularly in supercapacitors, as well as future perspectives. The main purpose of this review is to help the targeted audience to design their futuristic study in this desired field by providing information about the work done in the past few years.

High mass load of oxygen-enriched microporous hollow carbon spheres as electrode for supercapacitor with solar charging station application

Carbon materials modified with pores and heteroatoms have been pursued as promising electrode for supercapacitors due to the synergic storage of electric double-layer capacitance (EDLC) and pseudocapacitance. A vital problem that the actual effect of pores and heteroatoms on energy storage varies with the carbon matrix used presents in numerous carbon electrodes, but is ignored greatly, which limits their sufficient utilization. Moreover, most of modified carbon electrodes still suffer from severe capacitance degeneration under high mass load caused by the blocked surface and inaccessible bulk phase. Here, we shape an interconnected hollow carbon sphere (HCS) as the matrix by regulating and selectively-etching low molecular weight component in the inhomogeneous precursors, accompanied with the decoration of rich oxygen groups (15.9at%) and micropores (centering at 0.6-1.4 nm). Finite-element calculation and energy storage kinetics reveal the modified HCS electrode exposes accessible dual active surface with highly-matched electrons and ions for pores and oxygen groups to improve both EDLC and pseudocapacitance. Under a commercial-level load of 11.2 mg cm^-2, the HCS exhibits a high specific capacitance of 288.3 F g^-1 at 0.5 A g^-1, performing a retention of 91.8% relative to 314 F g^-1 under 2.8 mg cm^-2 load, applicable for solar charging station to efficiently drive portable electronics.

Green Synthesis of N doped Porous carbon/Carbon dots Composite as Metal-Free Catalytic Electrode Materials for Iodide Mediated Quasi-solid Flexible Supercapacitor

P-nitroaniline is adopted as versatile precursor for preparation of N-doped porous carbon (PC) and carbon dots (CDs) with enriched N functionalities, and the CDs are further anchored onto PC to...

Coordination Polymer Derived Porous Carbon Activated in Situ by the ZnCl2 Dot: Capacitances Greatly Enhanced by Redox-Activity Additives in Electrolytes

Herein, a 1D zinc coordination polymer [Zn(bibp)Cl₂]_∞ (CP-2-ZX) was assembled from the reaction of 4,4'-bis(imidazol-1-yl)-biphenyl (bibp) with ZnCl₂. Through a calcination-thermolysis strategy, sponge-like highly porous carbon AC-Zn-CP was prepared by employing the coralloid sample of CP-2-ZX as the precursor. For comparisons, a series of activated carbon (AC-n) was obtained by the similar heating process on the mixture of bibp with ZnCl₂ at different mass ratios. The results illustrate that the atomically dispersed ZnCl₂ dot in the 1D chain of CP-2-ZX has an in situ activation effect on the generation of AC-Zn-CP, which can greatly promote the porosity and achieve high-efficiency utilization of ZnCl₂. Therefore, the atomically dispersed activating agent provides a new method for environmentally friendly production of porous carbon materials. Significantly, the AC-Zn-CP electrode displays specific capacitance of 215 F g^-1 in 3 M KOH solution, which will be largely promoted to 1419 F g^-1 in the redox active electrolyte of K₃[Fe(CN)₆]/KOH. AC-Zn-CP also shows remarkable cycling stability (the capacity retention is 89.0% after 5000 cycles). Moreover, the fabricated symmetric supercapacitor owns a high energy density of 34.8 Wh kg^-1 at 785.5 W kg^-1. So, the AC-Zn-CP∩K₃[Fe(CN)₆] system has wide application prospects in supercapacitors.

One-Step Hydrothermal Synthesis of Nitrogen-Doped Reduced Graphene Oxide/Hausmannite Manganese Oxide for Symmetric and Asymmetric Pseudocapacitors

In this paper, the pseudocapacitive performance of nitrogen-doped and undoped reduced graphene oxide/tetragonal hausmannite nanohybrids (N-rGO/Mn₃O₄ and rGO/Mn₃O₄) synthesized using a one-pot hydrothermal method is reported. The nanohybrid electrode materials displayed exceptional electrochemical performance relative to their respective individual precursors (i.e., reduced graphene oxide (rGO), nitrogen-doped reduced graphene oxide (N-rGO), and tetragonal hausmannite (Mn₃O₄)) for symmetric pseudocapacitors. Among the two nanohybrids, N-rGO/Mn₃O₄ displayed greater performance with a high specific capacitance of 345 F g^-1 at a current density of 0.1 A g^-1, excellent specific energy of 12.0 Wh kg^-1 (0.1 A g^-1), and a high power density of 22.5 kW kg^-1 (10.0 A g^-1), while rGO/Mn₃O₄ demonstrated a high specific capacitance of 264 F g^-1 (0.1 A g^-1) with specific energy and power densities of 9.2 Wh kg^-1 (0.1 A g^-1) and 23.6 kW kg^-1 (10.0 A g^-1), respectively. Furthermore, the N-rGO/Mn₃O₄ nanohybrid exhibited an impressive pseudocapacitive performance when fabricated in an asymmetric configuration, having a stable potential window of 2.0 V in 1.0 M Na₂SO₄ electrolyte. The nanohybrid showed excellent specific energy and power densities of 34.6 Wh kg^-1 (0.1 A g^-1) and 14.01 kW kg^-1 (10.0 A g^-1), respectively. These promising results provide a good substance for developing novel carbon-based metal oxide electrode materials in pseudocapacitor applications.

B,N-Codoped Porous C with Controllable N Species as an Electrode Material for Supercapacitors

Manufacturing heteroatom-doped porous C with controllable N species is an important issue for supercapacitors. Herein, we report a low-cost and simplified strategy for synthesizing B,N-codoped porous C (BNPC) by a freeze-drying chitosan-boric acid aerogel beads and subsequent carbonization treatment. The BNPC samples were studied using various characterization technologies. The introduction of boric acid to chitosan successfully induced the formation of B,N-codoped C with a well-developed 3D interconnected porous structure. The B doping had a significant impact on the distribution of N species in the samples. Moreover, the good wettability of the sample resulting from B doping is favorable for electrolyte diffusion and ion transport. As a consequence, the optimal BNPC sample showed an excellent specific capacitance of 240 F g^-1 at 0.5 A g^-1 and an outstanding capacitance retention of 95.1% after 10000 cycles at 5 A g^-1. An assembled symmetrical supercapacitor displayed an energy density of 11.4 Wh kg^-1 at a power density of 250 W kg^-1. The proposed work provides a simple and effective method to obtain B,N-codoped C-based materials with high electrochemical performance.

Nitrogen Heterosubstitution in Graphene Nanoflakes: An Effective Approach to Improving Performance of Supercapacitors with Ionic Liquid Electrolyte

Abstract

Nitrogen-doped graphene nanoflakes with a high nitrogen content (6.6 at %) and developed mesoporosity were synthesized via pyridine pyrolysis. They were tested in a supercapacitor with a non-aqueous electrolyte: a 1.2 M solution of ionic liquid Et4N+TFSI− in acetonitrile. It was found that incorporation of nitrogen into the graphene layers nearly tripled the specific capacitance of the electrode, compared to the undoped nanoflakes.

The Effect of Modifications of Activated Carbon Materials on the Capacitive Performance: Surface, Microstructure, and Wettability

In this review, the efforts done by different research groups to enhance the performance of the electric double-layer capacitors (EDLCs), regarding the effect of the modification of activated carbon structures on the electrochemical properties, are summarized. Activated carbon materials with various porous textures, surface chemistry, and microstructure have been synthesized using several different techniques by different researchers. Micro-, meso-, and macroporous textures can be obtained through the activation/carbonization process using various activating agents. The surface chemistry of activated carbon materials can be modified via: (i) the carbonization of heteroatom-enriched compounds, (ii) post-treatment of carbon materials with reactive heteroatom sources, and (iii) activated carbon combined both with metal oxide materials dan conducting polymers to obtain composites. Intending to improve the EDLCs performance, the introduction of heteroatoms into an activated carbon matrix and composited activated carbon with either metal oxide materials or conducting polymers introduced a pseudo-capacitance effect, which is an additional contribution to the dominant double-layer capacitance. Such tricks offer high capacitance due to the presence of both electrical double layer charge storage mechanism and faradic charge transfer. The surface modification by attaching suitable heteroatoms such as phosphorus species increases the cell operating voltage, thereby improving the cell performance. To establish a detailed understanding of how one can modify the activated carbon structure regarding its porous textures, the surface chemistry, the wettability, and microstructure enable to enhance the performance of the EDLCs is discussed here in detail. This review discusses the basic key parameters which are considered to evaluate the performance of EDLCs such as cell capacitance, operating voltage, equivalent series resistance, power density, and energy density, and how these are affected by the modification of the activated carbon framework.

High Energy Density Heteroatom (O, N and S) Enriched Activated Carbon for Rational Design of Symmetric Supercapacitors

Carbon-based symmetric supercapacitors (SCs) are known for their high power density and long cyclability, making them an ideal candidate for power sources in new-generation electronic devices. To boost their electrochemical performances, deriving activated carbon doped with heteroatoms such as N, O, and S are highly desirable for increasing the specific capacitance. In this regard, activated carbon (AC) self-doped with heteroatoms is directly derived from bio-waste (lima-bean shell) using different KOH activation processes. The heteroatom-enriched AC synthesized using a pretreated carbon-to-KOH ratio of 1:2 (ONS@AC-2) shows excellent surface morphology with a large surface area of 1508 m²  g^-1 . As an SC electrode material, the presence of heteroatoms (N and S) reduces the interfacial charge-transfer resistance and increases the ion-accessible surface area, which inherently provides additional pseudocapacitance. The ONS@AC-2 electrode attains a maximum specific capacitance (C_sp ) of 342 F g^-1 at a specific current of 1 Ag^-1 in 1 m NaClO₄ electrolyte at the wide potential window of 1.8 V. Moreover, as symmetric SCs the ONS@AC-2 electrode delivers a maximum specific capacitance (C_sc ) of 191 F g^-1 with a maximum specific energy of 21.48 Wh kg^-1 and high specific power of 14 000 W kg^-1 and excellent retention of its initial capacitance (98 %) even after 10000 charge/discharge cycles. In addition, a flexible supercapacitor fabricated utilizing ONS@AC-2 electrodes and a LiCl/polyvinyl alcohol (PVA)-based polymer electrolyte shows a maximum C_sc of 119 F g^-1 with considerable specific energy and power.

Sustainable biomass-based hierarchical porous carbon for energy storage: A novel route to maintain electrochemically attractive natural structure of precursor

The development of sustainable and renewable energy storage devices with low cost and environment friendly features is an extremely urgent issue that needs to be solved. Herein, low-cost and sustainable biomass chitin, possessing natural fibrous, O/N-enriched and porous structure, was employed as a porous carbon (PC) precursor. However, a huge challenge in PC preparation is to maintain the natural electrochemically attractive structure of chitin while obtaining highly porous structure. In this study, by utilizing the molten protecting effect and micropore-creating ability of CuCl₂ 2H₂O, the obtained PCs maintain the natural structure, achieve high yield (46%), and simultaneously develop hierarchical pores with a specific surface area range of 1635-2381 m² g^-1, a tunable micropore volume ratio range of 63.5-96.8%, and high surface O/N contents (N: 3.1-9.0 wt% and O: 10.5-12.8 wt%). Benefiting from these excellent properties, optimized PC achieves a high specific capacitance of 286 F g^-1 at 0.5 A g^-1 and a remarkably high rate capability of 88% at 10 A g^-1; moreover, it even exhibits a rate capability of 80% at an ultrahigh current density of 50 A g^-1. The optimized PC-based supercapacitor assembled in Na₂SO₄ electrolyte shows a high energy density of 15.41 W h kg^-1 at 0.19 kW kg^-1 and achieves 76% energy density retention when the power density increased tenfold. Thus, this study presents a new way to fully utilize biomass, especially with electrochemically attractive natural structure, for developing advanced energy storage devices.

Nitrogen-Doped Mesoporous Carbon Microspheres by Spray Drying-Vapor Deposition for High-Performance Supercapacitor

Nitrogen-doped mesoporous carbon microspheres have been successfully synthesized via a spray drying-vapor deposition method for the first time, using commercial Ludox silica nanoparticles as hard templates. Compared to freeze-drying and air-drying methods, mesoporous carbon with a higher packing density can be achieved through the spray drying method. Vapor deposition of polypyrrole followed by carbonization and etching is beneficial for the generation of ultra-thin carbon network. The mesoporous carbon microspheres possess a mesopore-dominate (95%) high surface area of 1528 m² g⁻¹, a wall thickness of 1.8 nm, and a nitrogen content of 8 at% in the framework. Benefiting from the increased apparent density, high mesopore surface area, and considerable nitrogen doping, the resultant mesoporous carbon microspheres show superior gravimetric/volumetric capacitance of 533.6 F g⁻¹ and 208.1 F cm⁻³, good rate performance and excellent cycling stability in electric double-layer capacitors.

Boosting the charge transfer of Li2TiSiO5 using nitrogen-doped carbon nanofibers: towards high-rate, long-life lithium-ion batteries

Li2TiSiO5 (LTSO) has a theoretical specific capacity of up to 315 mA h g-1 with a suitable working potential (0.28 V vs. Li/Li+). However, the electronic structure of Li2TiSiO5 is firstly investigated by theoretical calculation based on the first-principles approach, and the results demonstrate that Li2TiSiO5 acts as the insulator for transferring electrons. Therefore, the framework with better conductivity is very essential for Li2TiSiO5 to enhance the charge transfer kinetics. Nitrogen-doped carbon encapsulated Li2TiSiO5 nanofibers (LTSO/NDC nanofibers) are obtained by using carbamide as a nitrogen source through an electrospinning technique. The nitrogen-doped carbon matrix with high electronic conductivity improves the electrochemical properties of LTSO significantly. The diffusion coefficient of lithium ions (DLi+) is greatly improved by manual calculation. The LTSO/NDC nanofiber electrode can deliver 371.7 mA h g-1 at 0.1 A g-1 and 361.1 mA h g-1 at 0.2 A g-1, and also shows a comparable cycle performance which could endure a long cycle over 800 cycles at 0.5 A g-1 almost without capacity decay. Hence, the LTSO/NDC nanofiber anode with a high rate and a long life provides a new direction for the realization of LTSO-based compounds in lithium ion batteries.

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal-organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

A Covalent Organic Framework for Fast-Charge and Durable Rechargeable Mg Storage

High-safety, low-cost, and high-volumetric-capacity rechargeable magnesium batteries (RMBs) are promising alternatives to lithium ion batteries. However, lack of high-power, high-energy, and stable cathodes for RMBs hinders their commercialization. Herein, an environmentally benign, low-cost, and sustainable covalent organic framework (COF) cathode for Mg storage is reported for the first time. It delivers a high power density of 2.8 kW kg^-1, a high specific energy density of 146 Wh kg^-1, and an ultralong cycle life of 3000 cycles with a very slow capacity decay rate of 0.0196% per cycle, representing one of the best cathodes to date. The comprehensive electrochemical analysis proves that triazine ring sites in the COF are redox centers for reversible reaction with magnesium ions, and the ultrafast reaction kinetics are mainly attributed to pseudocapacitive behavior. The high-rate Mg storage of the COF offers new opportunities for the development of ultrastable and fast-charge RMBs.

Far-Red Carbon Dots as Efficient Light-Harvesting Agents for Enhanced Photosynthesis

Sunlight utilization by plants via the photosynthesis process is limited to the visible spectral range. How to expand the utilization spectral range via construction of a hybrid photosynthetic system is a hot topic in this field. In this work, far-red carbon dots (FR-CDs) with excellent water solubility, good biocompatibility, high quantum yield (QY), and superior stability were prepared by a one-step microwave synthesis in 3 min. The as-prepared FR-CDs is an efficient converter transferring ultraviolet A (UV-A) light to 625-800 nm far-red emission, which can be directly absorbed and utilized by chloroplasts. Due to the broader spectral utilization of solar energy and Emerson effect, increased photosynthetic activity can be achieved both in vivo and in vitro when applied for Roman lettuce. The in vitro hybrid photosynthetic system via coating chloroplasts with FR-CDs presents higher electron transfer efficiency between PS II (photosystem II) to PS I (photosystem I), which consequently increases the ATP production. The in vivo experiment further confirms that FR-CDs-treated lettuce can induce a 28.00% higher electron transfer rate compared with the control group, which results in 51.14 and 24.60% enhancement of fresh and dry weights, respectively. This work is expected to provide a way for improving the conversion efficiency from solar energy to chemical energy. (PS II) to photosystem I (PS I), which consequently increases the ATP production. The in vivo experiment further confirms that FR-CDs-treated lettuce can induce a 28.00% higher electron transfer rate compared with the control group, which results in 51.14 and 24.60% enhancement of fresh and dry weights, respectively. This work is expected to provide a way for improving the conversion efficiency from solar energy to chemical energy.

Three-Dimensional Superlithiophilic Interphase for Dendrite-Free Lithium Metal Anodes

Lithium metal is among the most promising anode candidates of high-energy-density batteries. However, the formed dendrites result in low Coulombic efficiency and serious security issues. Designing lithiophilic sites is one of the effective strategies to control Li deposition. Herein, we propose a three-dimensional lithiophilic N-rich carbon nanofiber with the decoration of ZnO granules as a protective layer for a dendrite-free lithium metal anode. Theoretical evaluation indicates the synergistic effects of lithiophilic ZnO and N-containing functional groups enhance lithium adsorption and trigger uniform deposition. With the lithiophilic interlayer, the lithium deposition overpotential is only ∼20, 50, and 74 mV at 1, 3, and 6 mA cm^-2, respectively, which are much lower than those without the functional interlayer (∼55, 130, and 238 mV). The average Coulombic efficiency of lithium stripping and plating is up to ∼97.4% (94.0% for that without the interlayer) at 0.5 mA cm^-2. Meanwhile, the Li|LiFePO₄ full cell with the superlithiophilic interlayer demonstrates a high capacity retention rate of 99.6% (91.0% for that without the interlayer) over 200 cycles at 1 C. The introduction of the lithiophilic interphase could provide a convenient strategy and guidance to design the configuration for the practical application of Li metal batteries.

N-Doped 3D hierarchical carbon from resorcinol–formaldehyde–melamine resin for high-performance supercapacitors

N-Doped hierarchical porous carbons were fabricated by foaming and carbonizing resorcinol–formaldehyde–melamine resin and used as electrodes for flexible solid-state supercapacitors.

Metallic Organic Framework-Derived Fe, N, S co-doped Carbon as a Robust Catalyst for the Oxygen Reduction Reaction in Microbial Fuel Cells

Oxygen reduction reaction (ORR) provides a vital role for microbial fuel cells (MFCs) due to its slow reaction kinetics compared with the anodic oxidation reaction. How to develop new materials with low cost, high efficacy, and eco-friendliness which could replace platinum-based electrocatalysis is a challenge that we have to resolve. In this work, we accomplished this successfully by means of a facile strategy to synthesize a metallic organic framework-derived Fe, N, S co-doped carbon with FeS as the main phase. The Fe/S@N/C-0.5 catalyst demonstrated outstandingly enhanced ORR activity in neutral PBS and alkaline media, compared to that of commercial 20% Pt-C catalyst. Here, we started-up and operated two parallel single-chamber microbial fuel cells of an air cathode, and those cathode catalysts were Fe/S@N/C-0.5 and commercial Pt-C (20% Pt), respectively. Scanning electron microscopy (SEM) elaborated that the Fe/S@N/C-0.5 composite did not change the polyhedron morphology of ZIF-8. According to X-ray diffractometry(XRD) curves, the main crystal phase of the resulted Fe/S@N/C-0.5 was FeS. The chemical environment of N, S, and Fe which are anticipated to be the high-efficiency active sites of ORR for MFCs were investigated by X-ray photoelectron spectroscopic(XPS). Nitrogen adsorption/desorption techniques were used to calculate the pore diameter distribution. In brief, the obtained Fe/S@N/C-0.5 material exhibited a pronounced reduction potential at 0.861 V (versus Reversible Hydrogen Electrode(RHE)) in 0.1M KOH solution and –0.03 V (vs. SCE) in the PBS solution, which both outperform the benchmark platinum-based catalysts. Fe/S@N/C-0.5-MFC had a higher Open Circuit Voltage(OCV) (0.71 V), stronger maximum power density (1196 mW/m2), and larger output voltage (0.47 V) than the Pt/C-MFC under the same conditions.

Deep-Ultraviolet Emissive Carbon Nanodots

Deep-ultraviolet (DUV) emissive carbon nanodots (CNDs) have been designed theoretically and demonstrated experimentally based on the results of first-principles calculations using the density functional theory method. The emission of the CNDs is located in the range from 280 to 300 nm, which coincides well with the results of theoretical calculation results. The photoluminescence (PL) quantum yield (QY) of the CNDs is up to 31.6%, and the strong emission of the CNDs originates from core-state (π-π*) carriers' radiative recombination and surface passivation. Benefiting from the core-state emission and surface group passivation, the emission of the CNDs is independent of the excitation wavelength and ambient solvent. DUV light-emitting diodes (LEDs) have been fabricated based on the DUV emissive CNDs, and the LEDs can be used as the excitation source to excite blue, green, and red CNDs, indicating their potential application in DUV light sources. This work may provide a clue for the designing and realizing of DUV emissive CNDs, thus promising the potential application of CNDs in DUV light-emitting sources.

Mechanism of biomass activation and ammonia modification for nitrogen-doped porous carbon materials

The effect of chemical activation and NH₃ modification on activated carbons (ACs) was explored via two contrasting bamboo pyrolysis strategies involving either two steps (activation followed by nitrogen doping in NH₃ atmosphere) or one step (activation in NH₃ atmosphere) with several chemical activating reagents (KOH, K₂CO₃, and KOH + K₂CO₃). The ACs produced by the two-step method showed relatively smaller specific surface areas (∼90% micropores) and lower nitrogen contents. From the one-step method, the ACs had larger pore diameters with about 90% small mesopores (2-3.5 nm). Due to a promotion effect with the KOH + K₂CO₃ combination, the AC attained the greatest surface area (2417 m² g^-1) and highest nitrogen content (3.89 wt%), endowing the highest capacitance (175 F g^-1). The balance between surface area and nitrogen content recommends KOH + K₂CO₃ activation via the one-step method as the best choice for achieving both greener production process and better pore structure.

New Insights into the Electrochemistry Superiority of Liquid Na-K Alloy in Metal Batteries

The significant issues with alkali metal batteries arise from their poor electrochemical properties and safety problems, limiting their applications. Herein, TiO₂ nanoparticles embedded into N-doped porous carbon truncated ocatahedra (TiO₂ ⊂NPCTO) are engineered as a cathode material with different metal anodes, including solid Na or K and liquid Na-K alloy. Electrochemical performance and kinetics are systematically analyzed, with the aim to determine detailed electrochemistry. By using a galvanostatic intermittent titration technique, TiO₂ ⊂NPCTO/NaK shows faster diffusion of metal ions in insertion and extraction processes than that of Na-ions and K-ions in solid Na and K. The lower reaction resistance of liquid Na-K alloy electrode is also examined. The higher b-value of TiO₂ ⊂NPCTO/NaK confirms that the reaction kinetics are promoted by the surface-induced capacitive behavior, favorable for high rate performance. This superiority highly pertains to the distinct liquid-liquid junction between the electrolyte and electrode, and the prohibition of metal dendrite growth, substantiated by symmetric cell testing, which provides a robust and homogeneous interface more stable than the traditional solid-liquid one. Hence, the liquid Na-K alloy-based battery exhibits to better cyclablity with higher capacity, rate capability, and initial coulombic efficiency than solid Na and K batteries.