Advanced Carbon Materials Research Articles

Carbon Electrode Materials for Advanced Potassium‐Ion Storage

AbstractTremendous progress has been made in the field of electrochemical energy storage devices that rely on potassium‐ions as charge carriers due to their abundant resources and excellent ion transport properties. Nevertheless, future practical developments not only count on advanced electrode materials with superior electrochemical performance, but also on competitive costs of electrodes for scalable production. In the past few decades, advanced carbon materials have attracted great interest due to their low cost, high selectivity, and structural suitability and have been widely investigated as functional materials for potassium‐ion storage. This article provides an up‐to‐date overview of this rapidly developing field, focusing on recent advanced and mechanistic understanding of carbon‐based electrode materials for potassium‐ion batteries. In addition, we also discuss recent achievements of dual‐ion batteries and conversion‐type K−X (X=O2, CO2, S, Se, I2) batteries towards potential practical applications as high‐voltage and high‐power devices, and summarize carbon‐based materials as the host for K‐metal protection and possible directions for the development of potassium energy‐related devices as well. Based on this, we bridge the gaps between various carbon‐based functional materials structure and the related potassium‐ion storage performance, especially provide guidance on carbon material design principles for next‐generation potassium‐ion storage devices.

High sulfur-doped microporous carbon for high-rate potassium ion storage: Interspace design and solvent effect

Carbon materials as promising anode for potassium ion batteries (PIBs) suffer from low rate performance, which is attributed to sluggish K+ transport stemming from limited carbon interspace and elusive solvent effect. Herein, interspace design and solvent effect are investigated to resolve this issue. Through an innovative salt template assisted molten sulfur method, large hollow pores, massive micropores and expanded interlayer spacing are integrated in a high sulfur-doped porous carbon (S-PC), showing obviously higher rate capability (351.5 and 122.3 mA h g−1 at 0.1 and 20 A g−1, respectively) than pristine porous carbon (PC). Furthermore, the S-PC exhibits significantly-higher rate performance in ester-based electrolyte (1 M KFSI/EC + DEC) than in ether one (1 M KFSI/DME). Kinetic study demonstrates advantage of interspace design and ester-based electrolyte on promoting faster K+ transport. The explicit solvent effect on S-PC is further examined by XPS and HRTEM analyses, revealing a desirable inorganic KF-salt-dominated, thin solid electrolyte interface (SEI) layer in ester-based electrolyte. This work opens new avenues for precise design of advanced carbon materials for high-rate PIBs.

Pure and Metal‐confining Carbon Nanotubes through Electrochemical Reduction of Carbon Dioxide in Ca‐based Molten Salts

AbstractTo be successfully implemented, an efficient conversion, affordable operation and high values of CO2‐derived products by electrochemical conversion of CO2 are yet to be addressed. Inspired by the natural CaO‐CaCO3 cycle, we herein introduce CaO into electrolysis of SnO2 in affordable molten CaCl2‐NaCl to establish an in situ capture and conversion of CO2. In situ capture of anodic CO2 from graphite anode by the added CaO generates CaCO3. The consequent co‐electrolysis of SnO2 and CaCO3 confines Sn in carbon nanotube (Sn@CNT) in cathode and increases current efficiency of O2 evolution in graphite anode to 71.9 %. The intermediated CaC2 is verified as the nuclei to direct a self‐template generation of CNT, ensuring a CO2‐CNT current efficiency and energy efficiency of 85.1 % and 44.8 %, respectively. The Sn@CNT integrates confined responses of Sn cores to external electrochemical or thermal stimuli with robust CNT sheaths, resulting in excellent Li storage performance and intriguing application as nanothermometer. The versatility of the molten salt electrolysis of CO2 in Ca‐based molten salts for template‐free generation of advanced carbon materials is evidenced by the successful generation of pure CNT, Zn@CNT and Fe@CNT.

Pure and Metal-confining Carbon Nanotubes through Electrochemical Reduction of Carbon Dioxide in Ca-based Molten Salts.

To be successfully implemented, an efficient conversion, affordable operation and high values of CO2 -derived products by electrochemical conversion of CO2 are yet to be addressed. Inspired by the natural CaO-CaCO3 cycle, we herein introduce CaO into electrolysis of SnO2 in affordable molten CaCl2 -NaCl to establish an in situ capture and conversion of CO2 . In situ capture of anodic CO2 from graphite anode by the added CaO generates CaCO3 . The consequent co-electrolysis of SnO2 and CaCO3 confines Sn in carbon nanotube (Sn@CNT) in cathode and increases current efficiency of O2 evolution in graphite anode to 71.9 %. The intermediated CaC2 is verified as the nuclei to direct a self-template generation of CNT, ensuring a CO2 -CNT current efficiency and energy efficiency of 85.1 % and 44.8 %, respectively. The Sn@CNT integrates confined responses of Sn cores to external electrochemical or thermal stimuli with robust CNT sheaths, resulting in excellent Li storage performance and intriguing application as nanothermometer. The versatility of the molten salt electrolysis of CO2 in Ca-based molten salts for template-free generation of advanced carbon materials is evidenced by the successful generation of pure CNT, Zn@CNT and Fe@CNT.

Biomass Derived N-Doped Porous Carbon Made from Reed Straw for an Enhanced Supercapacitor.

Developing advanced carbon materials by utilizing biomass waste has attracted much attention. However, porous carbon electrodes based on the electronic-double-layer-capacitor (EDLC) charge storage mechanism generally presents unsatisfactory capacitance and energy density. Herein, an N-doped carbon material (RSM-0.33-550) was prepared by directly pyrolyzing reed straw and melamine. The micro- and meso-porous structure and the rich active nitrogen functional group offered more ion transfer and faradaic capacitance. X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) measurements were used to characterize the biomass-derived carbon materials. The prepared RSM-0.33-550 possessed an N content of 6.02% and a specific surface area of 547.1 m2 g-1. Compared with the RSM-0-550 without melamine addition, the RSM-0.33-550 possessed a higher content of active nitrogen (pyridinic-N) in the carbon network, thus presenting an increased number of active sites for charge storage. As the anode for supercapacitors (SCs) in 6 M KOH, RSM-0.33-550 exhibited a capacitance of 202.8 F g-1 at a current density of 1 A g-1. At a higher current density of 20 A g-1, it still retained a capacitance of 158 F g-1. Notably, it delivered excellent stability with capacity retention of 96.3% at 20 A g-1 after 5000 cycles. This work not only offers a new electrode material for SCs, but also gives a new insight into rationally utilizing biomass waste for energy storage.

Unveiling Superior Capacitive Behaviors of One-Pot Molten Salt-Engineered B, N Co-Doped Porous Carbon Sheets.

Heteroatom-doped porous carbon materials with distinctive surface properties and capacitive behavior have been accepted as promising candidates for supercapacitor electrodes. Currently, the researches mainly focus on developing facile synthetic method and unveiling the structure-activity relationship to further elevate their capacitive performance. Here, the B, N co-doped porous carbon sheet (BN-PCS) is constructed by one-pot pyrolysis of agar in KCl/KHCO3 molten salt system. In this process, the urea acts as directing agent to guide the formation of 2D sheet morphology, and the decomposition of KHCO3 and boric acid creates rich micro- and mesopores in the carbon framework. The specific capacitance of optimized BN-PCS reaches 361.1 F g-1 at a current density of 0.5 A g-1 in an aqueous KOH electrolyte. Impressively, the fabricated symmetrical supercapacitor affords a maximum energy density of 43.5Wh kg-1 at the power density of 375.0W kg-1 in 1.0mol L-1 TEABF4 /AN electrolyte. It also achieves excellent long-term stability with capacitance retention of 91.1% and Columbic efficiency of 100% over 10000 cycles. This study indicates one-pot molten salt method is effective in engineering advanced carbon materials for high-performance energy storage devices.

Coupling Uniform Pore Size And Multi‑Chemisorption Sites: Hierarchically Ordered Porous Carbon For Ultra‐Fast And Large Zinc Ion Storage

AbstractConstructing hierarchically ordered macro/meso−microporous structures of carbonaceous cathode with matchable pore size and adequate active sites is significant toward large Zn2+ storage, but remains a formidable challenge. Herein, a new perspective is reported for synthesizing phosphorus and nitrogen dual‐doped hierarchical ordered porous carbon (PN‐HOPC) by eliminating the micropore confinement effect and synchronously introducing multi‐chemisorption sites. The interconnected macropore can effectively facilitate long‐distance mass transfer, and meso−microporous wall can promote accessibility of active sites. Density functional theory (DFT) calculations identify that the P and N co‐doping markedly contributes to the reversible adsorption/desorption of zinc ions and protons. Consequently, the optimized PN‐HOPC exhibits outstanding Zn2+ storage capabilities in terms of high capacity (211.9 mAh g−1), superb energy density (169.5 Wh kg−1), and ultralong lifespan (99.3% retention after 60 000 cycles). Systematic ex situ measurements integrating with in situ Raman spectroscopy and electrochemical quartz crystal microbalance (EQCM) techniques elucidate that the superior electrochemical capability is ascribed to the synergistic effect of the Zn2+, H+, and SO42− co‐adsorption mechanism, as well as invertible chemical adsorption. This study not only provides new insights to design advanced carbon materials toward practical applications but also sheds lights on a deeper understanding of charge storage mechanism for zinc‐ion capacitors (ZICs).

Exploiting the Coordination Effect in Fe-Phenanthroline Complex for the Catalytic Carbonization of Phenanthroline toward the High Capacity Anode Grade Carbon

Aromatic organic molecules (AOMs) present an appealing precursor option for anode-grade hard carbon for sodium-ion batteries (SIBs) because of their prevalence, diverse chemical functionalities, and huge scope for nanostructure engineering at the molecular level. However, most small organic molecules decompose before actual carbonization is initiated unless reactions are carried out under high pressures or in the presence of catalysts. Herein, we report a facile carbonization of aromatic monomeric phenanthroline (phen) by exploiting the strong molecule-level coordination effect of the Fe-phen complex and in situ catalysis affected by Fe. With this carbonization strategy, we achieve better scalability with appreciable carbon yield, while carbonization of simple phen molecule returns zero carbon yields. The as-prepared N-doped microporous carbon (NMC) possesses desirable microstructural features with optimum nitrogen content to be employed as an anode for SIB. As an anode, the NMC delivers a high reversible capacity of 271 mAh g–1 at 100 mA g–1, an ultrahigh rate capability of 101 mAh g–1 at 1 A g–1, and a stable cycle life. The galvanostatic intermittent titration technique (GITT) depicts sodium ion diffusion coefficients of the order of ∼10–13 (cm2 s–1) in the intercalation region, which implies a faster sodium ion diffusion rate compared to most of the reported hard carbons. Given the vast diversity of AOMs, this work encourages new research interests to produce advanced carbon materials with nanostructure engineering at the molecular level for sodium-ion battery applications.

Transforming bio-oil into nitrogen-doped hierarchical porous carbons: Excellent oxygen reduction electrocatalysts for Zn-air batteries

Nitrogen-doped hierarchical porous carbons are considered as important substitutes for noble metal electrocatalysts for the oxygen reduction reaction (ORR) in green-energy devices. Herein, bio-oil, the liquid product of biomass pyrolysis, and urea were used as the carbon and nitrogen source based on a simple MgO template approach. The obtained carbons exhibited a micro-/meso-/macroporous structure, considerable specific surface area and abundance of Graphitic and Pyridinic nitrogen species, leading to the excellent ORR catalytic performance with a half-wave potential of 0.84 V. The assembled primary Zn-air battery displayed a maximum power density of 239.36 mW cm−2 and consistent discharging stability. This work verified the great potential of bio-oil as a sustainable and low-cost precursor of advanced functional carbon materials and was conducive to the large-scale production of efficient carbon-based ORR catalysts.

Recent Progress in Nanostructured Functional Materials and Their Applications II

Microstructure of the materials is essential to design new functional materials, especially from atomic scale to micron order structures. Many attempts have been carried out to give nanostructures and such structures have been analyzed using cutting-edge methods both theoretically and experimentally. In this report, recent trends in research on functional materials related to the micro-structures in nano-meter scale are reviewed by mainly introducing the contents of the special issue published in Materials Transactions, vol. 61, No. 8, in which following 6 categories of the topics are included; computational materials science, magnetic materials, advanced functional oxides, carbon and organic materials, and optical materials.

CO2 Pressure-Dependent Microstructure and Morphology of Carbon for Energy Storage: Unraveling the Role of CO2 in Green Synthesis of Carbon Materials

Advanced carbon materials have played an important function in the field of energy conversion and storage. The green and low-carbon synthesis of elemental carbon with controllable morphology and microstructure is the main problem for carbon materials. Herein, we develop a green and low-carbon method to synthesize porous carbon by reacting CO2 with LiAlH4 at low temperatures. The starting reaction temperatures are as low as 142, 121, and 104 °C for LiAlH4 reacting with 1, 30, and 60 bar CO2, respectively. For the elemental carbon, the porosity of elemental carbon gradually decreased, whereas its graphitization degree increased as the CO2 pressure increased from 1 bar to 60 bar. CO2 serves as one of the two reactants and the CO2 pressure can adjust the thermodynamic and kinetic properties of the formation reaction for synthesizing elemental carbon. The mechanism for CO2 pressure-dependent microstructure and morphology of carbon is discussed on the basis of the formation reaction of elemental carbon and gas blowing effect of H2 and CO2. The elemental carbon with different morphology and microstructure exhibits distinct electrochemical lithium storage performance including reversible capacity, rate capability, cycling stability, and Coulombic efficiency, owing to their different lithium storage mechanism. The elemental carbon synthesized at 30 bar CO2 delivers the highest reversible capacity of 506 mAh g−1 after 1000 cycles even at 1.0 A g−1. Advanced energy storage technology based on the green and low-carbon synthesis of carbon materials is a requisite for providing a stable and sustainable energy supply to meet the ever-growing demand for energy.

DEVELOPMENT OF SORPTION MATERIALS OF WIDE FUNCTIONAL PURPOSE IN THE V.I. VERNADSKII INSTITUTE OF GENERAL AND INORGANIC CHEMISTRY OF THE NAS OF UKRAINE

The review is devoted to the work, which were performed at the V.I. Vernadskii Institute of General and Inorganic Chemistry of the NAS of Ukraine according to the direction of the development of sorption naterials of wide functional purpose. All sorbents can be used in separation processes: due to their coarse dispersion and mechanical strength, they can be used as fillers for sorption columns.The direction of early works is the development of amorphous hydrophosphates and double hyd­rated oxides of multivalent metals, intended for the removal of toxic inorganic ions from water (arsenate-, chromate- and borate-anions, Cu2+, Pb2+, Cd2+cations etc.). Currently, attention is focused on the development of composite materials.The base of inorganic composites is hydrophosphate and oxide sorbents, and the modifiers are the advanced carbon materials, lithium-titanium and lithium-titanium-manganese spinels etc.Sorbents based on ion-exchange resins modified with inorganic ionites have also been developed.The combination of various components in composites makes it possible to obtain sorbents with improved properties (faster sorption, increased capacity and selectivity, sorption capacity in a wider pH range, easier regeneration) or multifunctional materials that sorb both inorganic and orga­nic compounds, for example, pesticides. Prospective field of research is the development of technologies that include not only the extraction of toxic and valuable components from liquids of natural, technological and biogenic origin, but also the regeneration of the sor­bent and processing of the concentrate to obtain commercial products.Thus, the integration of lithium sorption concentration into the process of reverse osmosis water desalination has been proposed. The processing of the solution formed during the regeneration of the sorbent includes the production of lithium carbonate and a complex fertilizer for acidic soils. Composites, the components of which are natural materials, are also in the focus of attention.Magnetic sorbents based on biopolymers, proposed for extraction of oil and oil products from water surfaces. Composites based on zeolites are used as containers for liquid fertilizers Another direction of research is the creation of composites - potential membrane modifiers for separation processes.

Green Synthesis of Advanced Carbon Materials Used as Precursors for Adsorbents Applied in Wastewater Treatment.

Huge amounts of vegetable waste, mainly resulting from the food industry, need large areas for storage, as they could cause hazardous environmental impact, leading to soil and water pollution or to CO2 emissions during accidental incineration. This work was aimed at recycling certain lignocellulosic waste (walnut shells, kernels of peach, apricot, and olive) to design advanced carbon material precursors (ACMP) to be used for obtaining nano-powders with high applicative potential in pollution abatement. Both waste and ACMP were characterized using proximate and elemental analysis, and by optical microscopy. Complex characterization of raw materials by FTIR, TGA-DTG, and SEM analysis were carried out. The ACMP were synthetized at 600-700 °C by innovative microwave heating technology which offers the advantages of lower energy consumption using 3.3 kW equipment at laboratory level. The ACMP ash < 3% and increased carbon content of 87% enabled the development of an extended pore network depending on degassing conditions during heating. TEM analysis revealed a well-developed porous structure of the synthesized ACMP carbonaceous materials. Due to the presence of oxygen functional groups, ACMPs exhibit adsorption properties highlighted by an iodine index of max. 500 mg/g and surface area BET of 300 m2/g, which make them attractive for removal of environmental pollutants such as dyes having molecule sizes below 2 nm and ions with pore dimensions below 1 nm, widely used industrially and found in underground waters (NO3-) or waste waters (SO42-).

Discriminating Active BN Sites in Coralloidal B, N Dual‐Doped Carbon Nano‐Bundles for Boosted Zn‐Ion Storage Capability

AbstractDual doping of boron (B) and nitrogen (N) provides an effective strategy to tailor chemical properties and electron distributions in the carbon plane, as well as customize the energy storage performance. Herein, a systematic theoretical and experimental study on rationally constructing coralloidal B, N dual‐doped carbon (BNC) nano‐bundles with abundant BN bonds for efficient Zn‐ion storage is presented. Compared with the single B or N doped sample and other dual‐doped B and N sites, the BN bond sites are found to boost the adsorption of Zn ions and enhance the electronic conductivity, which efficiently contribute to Zn‐ion storage. As expected, the optimized BNC nano‐bundles display greatly improved electrochemical performance, manifested by the high specific capacity of 204 mAh g−1 at 0.2 A g−1 and ultralong cycling stability for 40 000 cycles, outperforming most of the state‐of‐the‐art carbon cathodes. Moreover, a distinguished energy density of 178.7 Wh kg−1 and a high‐power density of 17.5 kW kg−1 are achieved with a constructed BNC//Zn device. This work not only provides critical insight for designing advanced carbon materials but also deepens the fundamental understanding of the governing mechanisms in dual‐doped carbon electrodes.

Research advancement in molten salt-mediated thermochemical upcycling of biomass waste

This paper discusses the research development and future challenges in molten salt-mediated thermochemical conversion of biomass waste into chemicals, fuels and advanced carbon materials.

Activating biomass carbon with metallurgical slag by pyrolysis in molten salt for high-performance supercapacitors.

Pyrolysis of sustainable biomass to advanced carbon materials for energy storage is key-enabling in energy and environmental sustainability. However, obtaining carbon materials with well-defined microstructure and composition for high-performance energy storage is extremely challenging. Herein, efficient activation of biomass carbon is realized by introducing extra metallurgical slag during pyrolysis of coconut shell in Na2CO3-K2CO3 molten salt. The molten salt guides the formation of carbon with a hierarchical honeycomb-like nanostructure, while the metallurgical slag facilitates enhanced doping of the heteroatom species, conjointly contributing to the increase of the specific surface area of carbon materials from 424 m2 g-1 to 1451 m2 g-1 and the extension of the single N dopant to multiple dopants of N, P, Zn and Co. Such adequate tuning of the microstructure and composition in the pyrolysis product increases the capacitance for supercapacitors from 30 F g-1 to 135 F g-1 at 0.5 A g-1. The results can provide new insights for the controllable upgradation of both biomass and waste industrial slag toward enhanced energy storage.

High-value utilization of lignin to prepare N,O-codoped porous carbon as a high-performance adsorbent for carbon dioxide capture

The concern for environmental sustainability has increased the interest in biomass materials for the synthesis of porous carbon, especially as an effective alternative and multifunctional adsorbent in the field of adsorption of a wide range of pollutants and carbon dioxide. Lignin has high carbon content, abundant aromatic rings and condensation bonds, which make it suitable as a precursor for carbon-containing materials. In this study, lignin was firstly precarbonized to achieve its degradation and efficient conversion, and then chemically activated by KOH to prepare a low-cost porous carbon materials with finely developed microporous structure, which showed excellent gas adsorption performance of 3.98 and 5.82 mmol/g at 1 bar, 298 K and 273 K, respectively. In addition to this, we have also investigated the dynamic sorption properties of the samples on CO2. The original lignin contains N,O functional groups that can be doped to the surface of the porous carbon, and previous studies have confirmed that the porosity and functional groups on the surface of the carbon material play a positive role in improving the defective and adsorption properties of the material. Our work provided a promising strategy for valorization of lignin as a precursor for producing advanced carbon materials.

Pyrolysis mechanism of composite binder composed of coal tar pitch and phenolic resin for carbon materials

The composite binder consisting of coal tar pitch (CTP) and phenolic resin (PR) has both low viscosity and high char yield, and it has great potential in the preparation of advanced carbon materials. However, the lack of understanding of its synergetic behavior and mechanism hinders the optimization of the preparation process. In this work, the co-pyrolysis of CTP and PR was systematically investigated. The char yield of the composite binder was confirmed to be remarkably higher than the weighted average of the two single binders. Furthermore, the calculated activation energy for the pyrolysis of the composite binder was higher than that of CTP and PR after 400 °C. The interaction and structure evolution mechanisms of composite binder were clarified. Specifically, the ortho-position of the phenoxy carbon in CTP cross-link with the para-position of the phenoxy carbon in PR by the methylene bridge, and the free polycyclic aromatic hydrocarbons stack onto the as-crosslinked polycyclic aromatics driven by the pancake bonds.

Fabrication of Graphdiyne/Graphene Composite Microsphere with Wrinkled Surface via Ultrasonic Spray Compounding and its Microwave Absorption Properties

Advanced carbon materials are constantly being used in the field of microwave absorption. Herein, in order to enrich the variety and expand the application fields of graphdiyne (GDY), the wrinkled graphene (RGO) nanosheet coated and embedded with GDY porous microspheres (RGO/GDY) are prepared by GDY synthesis, ultrasonic spray, and pyrolysis. The study finds that RGO and GDY have effective synergistic effects. The suitable pores and composition, conductive network formed by overlapping 0D and 2D materials, special surface and internal morphology design, and high-temperature activation process make RGO/GDY exhibit excellent impedance matching and attenuation capabilities. Under the best amount of GDY (20mg), the particle sizes of the microspheres (≈6µm), and filler content (27.5%), the minimum reflection loss (RLmin ) is -58 dB@8.3GHz, and the corresponding matching thickness is 2.7mm. The effective absorption bandwidth is 4.3GHz as the thickness is 1.9mm. By adjusting the thickness, the absorber can completely absorb microwaves of all the C, X, and Ku bands. The microwave absorbing mechanisms are elucidated. GDY materials are first applied to the field of microwave absorption, enhancing the absorption performance of RGO/GDY. It provides a new way to manufacture electromagnetic wave absorbers with satisfactory performance.

Hydrothermal carbonization of glucose: Secondary char properties, reaction pathways, and kinetics

Hydrothermal carbonization (HTC) is a promising green route to synthesize carbon materials and valorize biomass waste. The intricacy behind the conversion is enormous, requiring investigations of the mechanisms starting from the fundamentals. Intending to contribute to the rudiments of HTC, this work provides a systematic insight into the decomposition of glucose during HTC. The interest in glucose stems from its nature, indeed it is: one of the building blocks of biomass, a substrate for producing advanced carbon materials, and a precursor of secondary char - the solid phase deriving from re-polymerization and condensation reactions from the liquid phase back onto solid. The work approaches the glucose HTC holistically, focusing on kinetics and characterization of the products. A 1.1 M glucose solution was hydrothermally carbonized over several operating conditions (180–270 °C and 0–8 h) with analysis of the solid and liquid phases. Results show that hydrochar changes significantly with time only at 180 °C. Above 180 °C, the solid yield stabilizes at 47–50 % and the carbon content at 67–70 %. The time-evolution of liquid intermediates (like HMF and small carboxylic acids) detected through NMR enabled the deduction of formation pathways and calibration of a higher-order kinetics model. Meanwhile, SEM and Raman spectra show hydrochars characterized by typical nano/microspheres, having a size distribution dependent on operating conditions and mainly an amorphous structure, with a tendency towards graphitization as the HTC severity increases. All the hydrochars show photoluminescence, a functionality that opens to several application possibilities.