A Bimetallic Organic Framework with Mn in MIL-101(Cr) for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) show excellent performance in terms of specific capacity and energy density. However, the cyclic stability of LSBs is compromised due to the "shuttle effect", which hinders the practical applications of LSBs. Herein, a metal-organic framework (MOF) based on Cr ions as the main body composition, commonly known as MIL-101(Cr), was utilized to minimize the shuttle effect and improve the cyclic performance of LSBs. To obtain MOFs with a certain adsorption capacity for lithium polysulfide and a certain catalytic capacity, we propose an effective strategy of incorporating sulfur-loving metal ions (Mn) into the skeleton to enhance the reaction kinetics at the electrode. Based on the oxidation doping method, Mn²⁺ was uniformly dispersed in MIL-101(Cr) to produce bimetallic Cr₂O₃/MnO_x as a novel sulfur-carrying cathode material. Then, a sulfur injection process was carried out by melt diffusion to obtain the sulfur-containing Cr₂O₃/MnO_x-S electrode. Moreover, an LSB assembled with Cr₂O₃/MnO_x-S showed improved first-cycle discharge (1285 mAh·g^-1 at 0.1 C) and cyclic performance (721 mAh·g^-1 at 0.1 C after 100 cycles), and the overall performance was much better than that of monometallic MIL-101(Cr) as a sulfur carrier. These results revealed that the physical immobilization method of MIL-101(Cr) positively affected the adsorption of polysulfides, while the bimetallic composite Cr₂O₃/MnO_x formed by the doping of sulfur-loving Mn²⁺ into the porous MOF produced a good catalytic effect during LSB charging. This research provides a novel approach for preparing efficient sulfur-containing materials for LSBs.

Biowaste-Derived Heteroatom-Doped Porous Carbon as a Sustainable Electrocatalyst for Hydrogen Evolution Reaction

Heteroatom-doped porous carbon material (H-PCM) was synthesized using Anacardium occidentale (cashew) nut’s skin by a simple pyrolysis route. The resulting H-PCM was thoroughly characterized by various analytical techniques such as field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray (EDX) spectroscopy, high-resolution transmittance electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The obtained results strongly demonstrated that the synthesized H-PCM exhibited a porous nature, continuous sponge-like and sheet-like smooth morphology, and a moderate degree of graphitization/crystallinity with oxygen-, nitrogen-, and sulfur-containing functionalities in the carbon matrix. After the structural confirmation, as-prepared H-PCM has used a sustainable electrocatalyst for hydrogen evolution reaction (HER) because the metal-free carbonaceous catalysts are one of the most promising candidates. The H-PCM showed excellent HER activities with a lowest Tafel slope of 75 mV dec−1 and durable stability in 0.5 M H2SO4 aqueous solution. Moreover, this work provides a versatile and effective strategy for designing excellent metal-free electrocatalysts from the cheapest biowaste/biomass for large-scale production of hydrogen gas through electrochemical water splitting.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Preparation of Sulfur-doped Carbon for Supercapacitor Applications: A Review

Electrochemical capacitors, also known as supercapacitors (SCs), have lately played an important role in energy storage and conversion systems due to their specific characteristics such as high strength, durability, and environmental friendliness. A wide range of materials is used as electrodes for SC applications because the electrochemical efficiency is primarily determined by the electrode materials used. Carbonaceous materials with unique surface, chemical, electrochemical, and electronic characteristics have become attractive for energy storage research, but they cannot meet the rising need for high specific energy and specific power. Besides, heteroatom-doped carbon materials have shown pseudocapacitance characteristics and improved specific energy, specific power, and conductivity. This makes them more adaptable in SC application. Among different heteroatom doping of carbon, S-doped carbon has gained considerable attention in SC applications due to its unpaired electrons and easily polarizable nature. S-doped carbon materials-based SCs have demonstrated enhanced surface wettability, improved conductivity, and induced pseudocapacitance effect, thereby delivering improved specific energy and specific power. Many reports on S-doped carbon for SC applications have been published, but there is no specific Review on the preparation of S-doped carbon for SC applications. This Review focuses on recent developments in the field of SC electrodes made from S-doped carbon materials. Herein, the preparation methods and applications of S-doped carbon for SCs were summarized following a brief discussion of different electrochemical characterization techniques of SCs. Finally, the challenges of S-doped carbon materials and their potential prospects were discussed to give crucial insights into the favorable factors for future innovations of SC electrodes. This Review aims to provide insight for further research on the preparation of S-doped carbon for electrochemical energy storage applications.

Improvement of Nanostructured Polythiophene Film Uniformity Using a Cruciform Electrode and Substrate Rotation in Atmospheric Pressure Plasma Polymerization

In atmospheric pressure (AP) plasma polymerization, increasing the effective volume of the plasma medium by expanding the plasma-generating region within the plasma reactor is considered a simple method to create regular and uniform polymer films. Here, we propose a newly designed AP plasma reactor with a cruciform wire electrode that can expand the discharge volume. Based on the plasma vessel configuration, which consists of a wide tube and a substrate stand, two tungsten wires crossed at 90 degrees are used as a common powered electrode in consideration of two-dimensional spatial expansion. In the wire electrode, which is partially covered by a glass capillary, discharge occurs at the boundary where the capillary terminates, so that the discharge region is divided into fourths along the cruciform electrode and the discharge volume can successfully expand. It is confirmed that although a discharge imbalance in the four regions of the AP plasma reactor can adversely affect the uniformity of the polymerized, nanostructured polymer film, rotating the substrate using a turntable can significantly improve the film uniformity. With this AP plasma reactor, nanostructured polythiophene (PTh) films are synthesized and the morphology and chemical properties of the PTh nanostructure, as well as the PTh-film uniformity and electrical properties, are investigated in detail.

Sulfur-Doped Carbons from Durian Peels, Their Surface Characteristics, and Electrochemical Behaviors

Durian peels are an agricultural waste in Asian countries, including Thailand, Indonesia, and Malaysia, which can be used as a precursor for the production of activated carbon. The objective of this work is to produce activated carbon from durian peels by chemical activation using sodium sulfite (Na2SO3) as an activating and sulfur-doping agent. The process parameter investigated in this study was the activation temperature (500-900 °C) at a fixed impregnation ratio (durian to activating agent of 1:1, by weight). Specific surface areas and pore structures were determined by nitrogen adsorption and desorption measurements, and elemental compositions were characterized by CHNSO analysis. The chemical structure and surface functionality were examined by X-ray photoelectron spectroscopy. The electrochemical behavior of the obtained activated carbon was characterized in 6 M KOH using a three-electrode configuration. It was found that the sulfur content decreases with activation temperature. In contrast, the specific surface area of the activated carbon increases with activation temperature. However, the sample activated at 900 °C with the highest specific surface area (1499 m2 g-1) has a lower specific capacitance (166 F g-1) than the one activated at 700 °C (183 F g-1). This could be due to the presence of a pseudocapacitance caused by the organic sulfur functional groups such as thiophene, sulfone, and sulfoxide, which can trigger a surface redox reaction, leading to a higher capacitance.

Azo-dye derived oxidized-nitrogen rich carbon sheets with high adsorption capability for dye effluent under both batch and continuous conditions

The removal of methyl blue (MB) from wastewater using graphene and its derivative is very successful due to their high aromaticity which drives adsorption via π-π and electron-donor-acceptor (EDA) interactions; however, graphene is expensive and difficult to synthesize, which limit its practical application. Meanwhile, low aromatic carbon materials (LACM) derived from farm-water and other materials are cheaper and easier to synthesize but have limited π-π and EDA interactions and low adsorption capacity. Herein, we demonstrate that LACM with oxidized-nitrogen (N-O^-) functionality overcomes this limitation via chemisorption of MB through a combination of hydrophobic-hydrophobic interactions and EDA interactions. This is confirmed using XPS analysis of LACM/N-O^- post MB adsorption. Consequently, a remarkable adsorption capacity of 3904 mg g^-1 is achieved under batch condition which is the highest ever reported for any MB adsorbent. Furthermore, LACM/N-O^- works equally well under continuous-flow adsorption conditions which shows its practicability. Amongst several LACM precursors tested, only Azo-dyes are able to generate LACM/N-O^- implying that the NN moiety is key to N-O^- formation. A carbonization temperature of 700 °C generates the highest N-O^- sites hence the highest adsorption capacity. Characterization of LACM/N-O^- is done mainly using BET, XPS, Raman, TGA, and FTIR analysis.

Ultrafast Room Temperature Synthesis of Porous Polythiophene via Atmospheric Pressure Plasma Polymerization Technique and Its Application to NO2 Gas Sensors

New nanostructured conducting porous polythiophene (PTh) films are directly deposited on substrates at room temperature (RT) by novel atmospheric pressure plasma jets (APPJs) polymerization technique. The proposed plasma polymerization synthesis technique can grow the PTh films with a very fast deposition rate of about 7.0 μm·min⁻¹ by improving the sufficient nucleation and fragment of the thiophene monomer. This study also compares pure and iodine (I₂)-doped PTh films to demonstrate the effects of I₂ doping. To check the feasibility as a sensing material, NO₂-sensing properties of the I₂-doped PTh films-based gas sensors are also investigated. As a result, the proposed APPJs device can produce the high density, porous and ultra-fast polymer films, and polymers-based gas sensors have high sensitivity to NO₂ at RT. Our approach enabled a series of processes from synthesis of sensing materials to fabrication of gas sensors to be carried out simultaneously.

N/S co-doped coal-based porous carbon spheres as electrode materials for high performance supercapacitors

N/S co-doped porous carbon spheres were prepared using one step strategy for high performance supercapacitors.

A dual metal organic framework based on copper-iron clusters integrated sulphur doped graphene as a porous material for supercapacitor with remarkable performance characteristics

Herein, a novel bimetallic metal organic framework (MOF) using copper and iron as the metal centers with 1,3,5-tricarboxylic acid as a ligand (CuFeBTC) and its composite with sulphur doped graphene (S-GNS) have been investigated for supercapacitive performance. The synthesis of materials has been carried out using a facile wet chemical route. The physicochemical characterization of the materials employing various structural and surface techniques has been performed which confirms the successful formation of nanocomposite. The capacitive behavior of CuFeBTC, S-GNS and CuFeBTC/S-GNS has been systematically examined using 1 M Na₂SO₄ as an electrolyte in a three and two electrode assembly. The electrochemical studies reveal that CuFeBTC/S-GNS electrode demonstrates highest specific capacitance of 1164.3 F g^-1 at 0.5 A g^-1 with suffice rate capability as compared to CuFeBTC and S-GNS electrodes. Moreover, a symmetric supercapacitor is configured using the CuFeBTC/S-GNS nanocomposite electrodes which deliver remarkable energy and power output of 96.57 Wh kg^-1 and 1595.12 W kg^-1 at an operating voltage of 1.8 V. The as-fabricated symmetric supercapacitor displays competent energy storage retention of 50.2 Wh kg^-1 even at current density of 20.0 A g^-1 with high power density 26973.13 W kg^-1. These deliverables epitomize the latest performance record of bimetallic MOFs based supercapacitors, suggesting that CuFeBTC/S-GNS is a promising active material for high performance electrochemical energy storage applications.

Nitrogen and Sulfur Self-Doped Activated Carbon Directly Derived from Elm Flower for High-Performance Supercapacitors

N,S-Doped activated carbon was directly prepared via a facile and cost-efficient hydrothermal reaction, followed by alkali activation of elm flower (EL)-derived biomass. The EL-derived activated carbon (ELAC) had N and S contents of 2.21 and 6.06 atom %, respectively, in addition to a high Brunauer-Emmett-Teller (BET) surface area of 2048.6 m² g^-1 and moderate pore volume of 0.88 cm³ g^-1. Owing to its high BET surface area and N/S functional groups, ELAC achieved a specific capacitance of 275 F g^-1 at a current density of 1 A g^-1 and retained a capacitance of 216 F g^-1 at 20 A g^-1. In addition, a symmetric supercapacitor based on N,S-self-doped ELAC electrode provided a capacitance of 62 F g^-1 at a current density of 10 A g^-1, with maximum energy and power densities of 16.8 Wh kg^-1 and 600 W kg^-1, respectively. The capacitance retention was also high, at 87.2%, at 4 A g^-1 after 5000 cycles.

MoS2 /MoOx -Nanostructure-Decorated Activated Carbon Cloth for Enhanced Supercapacitor Performance

MoS₂ /MoO_x nanostructures were grown on activated carbon cloth through a facile one-step microwave-assisted hydrothermal method. The growth of MoS₂ /MoO_x on activated carbon cloth creates a unique structure that favors ion intercalation. The conductive activated carbon cloth, MoO_3-x , and monoclinic MoO₂ provide fast electron transport, whereas the MoS₂ nanosheets/MoO_3-x nanoparticles structure improves the capacitance. As a result, MoS₂ /MoO_x -nanostructure-decorated activated carbon cloth shows a high specific capacitance of 230 F g^-1 at a scan rate of 5 mV s^-1 with a low contact resistance of approximately 1.91 Ω. Moreover, the activated carbon cloth acts as a template for the growth of a perpendicular MoS₂ layer, which gives an excellent utilization rate of the active MoS₂ /MoO_x material. We also demonstrate that the MoS₂ /MoO_x /activated carbon cloth nanocomposite shows excellent electrochemical stability with retention up to 128 % after 1500 cycles. Finally, we show the use of a microwave-assisted hydrothermal method for the synthesis of the MoS₂ /MoO_x /activated carbon cloth nanocomposite as an alternative and clean route to improve the kinetics of the intercalation redox reaction.

A high-performance asymmetric supercapacitor based on vanadyl phosphate/carbon nanocomposites and polypyrrole-derived carbon nanowires

A novel asymmetric supercapacitor device in an aqueous electrolyte is fabricated using a vanadyl phosphate/carbon nanocomposite as the positive electrode and a polypyrrole-derived carbon nanowire as the negative electrode. The vanadyl phosphate/carbon nanocomposites are synthesized by a simple two-step approach in which layered VOPO₄·2H₂O is first intercalated by dodecylamine and then annealed at high temperature, leading to the in situ carbonization of the intercalated dodecylamine. It is found that the sample in which the incorporated carbon with a high degree of graphitization exhibits a high specific capacitance of 469 F g^-1 at a current density of 1 A g^-1 and excellent rate performance (retained 77% capacitance at 10 A g^-1). A polypyrrole-derived carbon nanowire is synthesized by the direct carbonization of nanowire-shaped polypyrrole, revealing a rough surface of nanowire-like frameworks and good electrochemical behavior. Taking advantage of both positive and negative materials, the assembled asymmetric supercapacitor device exhibits a high energy density of 30.6 W h kg^-1 at a high power density of 813 W kg^-1 in a wide voltage region of 0-1.6 V, as well as a good electrochemical stability (84.3% capacitance retention after 5000 cycles). The present work can shed light on the fabrication of novel asymmetric supercapacitors with high-performance.

Solvent-Induced Cadmium(II) Metal-Organic Frameworks with Adjustable Guest-Evacuated Porosity: Application in the Controllable Assembly of MOF-Derived Porous Carbon Materials for Supercapacitors

In this work, five new cadmium metal-organic frameworks (Cd-MOFs 1-5) have been synthesized from solvothermal reactions of Cd(NO₃ )₂ ⋅4 H₂ O with isophthalic acid and 1,4-bis(imidazol-1-yl)-benzene under different solvent systems of CH₃ OH, C₂ H₅ OH, (CH₃ )₂ CHOH, DMF, and N-methyl-2-pyrrolidone (NMP), respectively. Cd-MOF 1 shows a 3D diamondoid framework with 1D rhombic and hexagonal channels, and the porosity is 12.9 %. Cd-MOF 2 exhibits a 2D (4,4) layer with a 1D parallelogram channel and porosity of 23.6 %. Cd-MOF 3 has an 8-connected dense network with the Schäfli symbol of [4²⁴ ⋅6⁴ ] based on the Cd₆ cluster. Cd-MOFs 4-5 are isomorphous, and display an absolutely double-bridging 2D (4,4) layer with 1D tetragonal channels and porosities of 29.2 and 28.2 %, which are occupied by DMF and NMP molecules, respectively. Followed by the calcination-thermolysis procedure, Cd-MOFs 1-5 are employed as precursors to prepare MOF-derived porous carbon materials (labeled as PC-me, PC-eth, PC-ipr, PC-dmf and PC-nmp), which have the BET specific surface area of 23, 51, 10, 122, and 96 m²  g^-1 , respectively. The results demonstrate that the specific surface area of PCs is tuned by the porosity of Cd-MOFs, where the later is highly dependent on the solvent. Thereby, the specific surface area of PCs could be adjusted by the solvent used in the synthese of MOF precusors. Significantly, PCs have been further activated by KOH to obtain activated carbon materials (APCs), which possess even higher specific surface area and larger porosity. After a series of characterization and electrochemical investigations, the APC-dmf electrode exhibits the best porous properties and largest specific capacitances (153 F g^-1 at 5 mV s^-1 and 156 F g^-1 at 0.5 Ag^-1 ). Meanwhile, the APC-dmf electrode shows excellent cycling stability (ca. 84.2 % after 5000 cycles at 1 Ag^-1 ), which can be applied as a suitable electrode material for supercapacitors.