Flexible 3D carbon cloth as a high-performing electrode for energy storage and conversion

Paper-based Electrochemical Sensor Integrated with Gold Nanoparticle-Decorated Carbon Cloth as a Working Electrode for Nitric Oxide Detection in Artificial Tears

Nitric oxide (NO) in human tears regulates numerous ocular surface processes, such as tear generation, corneal wound healing, conjunctival vascular tone, and so forth. Any deviation from its normal concentration is linked to various ocular syndromes, including microbial keratitis, conjunctivitis, pterygium, dry eye, retinitis, glaucoma, and so forth. Therefore, precise monitoring of NO in tears can be considered as a potential biomarker for ocular diseases. Here, we report a highly sensitive and selective electrochemical NO sensor using carbon ink-based electrodes. Counter, working (WE), and reference electrodes have been designed and painted on a butter paper by using carbon ink. To improve the sensing performance, the WE has been modified with a gold nanoparticle (Au NP)-deposited carbon cloth (CC). Such a paper-based sensor demonstrated high sensitivity of ∼0.34 μA μM-1 cm-2, ultralow detection limit of ∼2.35 nM, wide linear range of 10 nM-0.4 mM, and fast response time (0.35 s). The sensor also showed excellent stability and selectivity toward the interfering agents in human body fluids. Such a low-cost, flexible paper-based sensor was employed for the detection of NO in artificial tears.

Monolithic Microparticles Facilitated Flower-Like TiO2 Nanowires for High Areal Capacity Flexible Li-Ion Batteries

Flexible lithium-ion batteries (FLIBs) are intensively studied using free-standing transition metal oxides (TMOs)-based anode materials. However, achieving high areal capacity TMO-based anode materials is yet to be effectively elucidated owing to the poor adhesion of the active materials to the flexible substrate resulting in low active mass loading, and hence low areal capacity is realized. Herein, a novel monolithic rutile TiO2 microparticles on carbon cloth (ATO/CC) that facilitate the flower-like arrangement of TiO2 nanowires (denoted ATO/CC/OTO) is demonstrated as high areal capacity anode for FLIBs. The optimized ATO/CC/OTO anode exhibits high areal capacity (5.02 mAh cm-2@0.4 mA cm-2) excellent rate capability (1.17 mAh cm-2@5.0 mA cm-2) and remarkable cyclic stability (over 500 cycles). A series of morphological, kinetic, electrochemical, in situ Raman, and theoretical analyses reveal that the rational phase boundaries between the microparticles and nanowires contribute to promoting the Li storage activity. Furthermore, a 16.0 cm2 all-FLIB pouch cell assembled based on the ATO/CC/OTO anode and LiNiCoMnO2 cathode coated on ATO/CC (ATO/CC/LNCM) exhibits impressive flexibility under different folding conditions, creating opportunity for the development of high areal capacity anodes in future flexible energy storage devices.

Single-Atomic Co-N4 Sites with CrCo Nanoparticles for Metal-Air Battery-Driven Hydrogen Evolution

Designing highly active and robust earth abundant trifunctional electrocatalysts for energy storage and conversion applications remain an enormous challenge. Herein, we report a trifunctional electrocatalyst (CrCo/CoN4@CNT-5), synthesized at low calcination temperature (550 °C), which consists of Co-N4 single atom and CrCo alloy nanoparticles and exhibits outstanding electrocatalytic performance for the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The catalyst is able to deliver a current density of 10 mA cm-2 in an alkaline electrolytic cell at a very low cell voltage of ∼1.60 V. When the catalyst is equipped in a liquid rechargeable Zn-air battery, it endowed a high open-circuit voltage with excellent cycling durability and outperformed the commercial Pt/C+IrO2 catalytic system. Furthermore, the Zn-air battery powered self-driven water splitting system is displayed using CrCo/CoN4@CNT-5 as sole trifunctional catalyst, delivering a high H2 evolution rate of 168 μmol h-1. Theoretical calculations reveal synergistic interaction between Co-N4 active sites and CrCo nanoparticles, favoring the Gibbs free energy for H2 evolution. The presence of Cr not only enhances the H2O adsorption and dissociation but also tunes the electronic property of CrCo nanoparticles to provide optimized hydrogen binding capacity to Co-N4 sites, thus giving rise to accelerated H2 evolution kinetics. This work highlights the importance of the presence of small quantity of Cr in enhancing the electrocatalytic activity as well as robustness of single-atom catalyst and suggests the design of the multifunctional robust electrocatalysts for long-term H2 evolution application.

Fabrication of well-aligned Co-MOF arrays through a controlled and moderate process for the development of a flexible tetrabromobisphenol A sensor

Tetrabromobisphenol A (TBBPA) has attracted a great deal of attention due to its side effects and potential bioaccumulation properties. It is of great importance to construct and develop novel electrochemical sensors for the sensitive and selective detection of TBBPA. In the present study, cobalt (Co) based metal-organic frameworks (MOFs) were synthesized on carbon cloth (CC) by using cobalt nitrate hexahydrate and 2-methylimidazole. The morphological characterization was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that Co-MOFs/CC have a leaf-like structure and abundant surface functional groups. The electrochemical properties of the sensor were investigated by differential pulse voltammetry (DPV). The effects of different ratios of metal ions to organic ligands, reaction temperature, time, concentration, pH value of the electrolyte, and incubation time on the oxidation peak current of TBBPA were studied. Under the optimal conditions, the linear range of the designed sensor was 0.1 μM-100 μM, and the limit of detection was 40 nM. The proposed sensor is simple, of low cost and efficient, which can greatly facilitate the detection tasks of environmental monitoring workers.

An electrochemical sensor founded on heterogeneous MXene & MOF composite for tanshinol sensing

A new kind of electrochemical sensor based on the MXene & MOF composite-modified carbon cloth was prepared firstly by self-assembly through hydrogen bonds, and then by air-annealing process for detection. The preparation processing introduced chemical bonds between MXene and MOF, which remarkably enhanced the electron transfer ability. Accordingly, combing the unique features of MXene and MOF themselves, the novel electrochemical sensor exhibited exceptional performance to detect tanshinol. Via differential pulse voltammetry, we could obtain a linear tanshinol concentration range of 0.08-8 μM and the limit of detection is 0.034 μM. Furthermore, this developed electrochemical sensor could determine concentrations of tanshinol in real Chinese herbal samples, confirming its practicability and reliability.

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

Short-Time Magnetron Sputtering for the Development of Carbon-Palladium Nanocomposites

In recent nanomaterials research, combining nanoporous carbons with metallic nanoparticles, like palladium (Pd), has emerged as a focus due to their potential in energy, environmental and biomedical fields. This study presents a novel approach for synthesizing Pd-decorated carbons using magnetron sputter deposition. This method allows for the functionalization of nanoporous carbon surfaces with Pd nano-sized islands, creating metal-carbon nanocomposites through brief deposition times of up to 15 s. The present research utilized direct current magnetron sputtering to deposit Pd islands on a flexible activated carbon cloth substrate. The surface chemistry, microstructure, morphology and pore structure were analyzed using a variety of material characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, gas sorption analysis and scanning electron microscopy. The results showed Pd islands of varying sizes distributed across the cloth's carbon fibers, achieving high-purity surface modifications without the use of chemicals. The synthesis method preserves the nanoporous structure of the carbon cloth substrate while adding functional Pd islands, which could be potentially useful in emerging fields like hydrogen storage, fuel cells and biosensors. This approach demonstrates the possibility of creating high-quality metal-carbon composites using a simple, clean and economical method, expanding the possibilities for future nanomaterial-based applications.

Role of microbial electrosynthesis system in CO2 capture and conversion: a recent advancement toward cathode development

Microbial electrosynthesis (MES) is an emerging electrochemical technology currently being researched as a CO₂ sequestration method to address climate change. MES can convert CO₂ from pollution or waste materials into various carbon compounds with low energy requirements using electrogenic microbes as biocatalysts. However, the critical component in this technology, the cathode, still needs to perform more effectively than other conventional CO₂ reduction methods because of poor selectivity, complex metabolism pathways of microbes, and high material cost. These characteristics lead to the weak interactions of microbes and cathode electrocatalytic activities. These approaches range from cathode modification using conventional engineering approaches to new fabrication methods. Aside from cathode development, the operating procedure also plays a critical function and strategy to optimize electrosynthesis production in reducing operating costs, such as hybridization and integration of MES. If this technology could be realized, it would offer a new way to utilize excess CO₂ from industries and generate profitable commodities in the future to replace fossil fuel-derived products. In recent years, several potential approaches have been tested and studied to boost the capabilities of CO₂-reducing bio-cathodes regarding surface morphology, current density, and biocompatibility, which would be further elaborated. This compilation aims to showcase that the achievements of MES have significantly improved and the future direction this is going with some recommendations. Highlights - MES approach in carbon sequestration using the biotic component.- The role of microbes as biocatalysts in MES and their metabolic pathways are discussed.- Methods and materials used to modify biocathode for enhancing CO₂ reduction are presented.

Recent Advances in Metal-Organic Frameworks (MOFs) and Their Composites for Non-Enzymatic Electrochemical Glucose Sensors

In recent years, with pressing needs such as diabetes management, the detection of glucose in various substrates has attracted unprecedented interest from researchers in academia and industry. As a relatively new glucose sensor, non-enzymatic target detection has the characteristics of high sensitivity, good stability and simple manufacturing process. However, it is urgent to explore novel materials with low cost, high stability and excellent performance to modify electrodes. Metal-organic frameworks (MOFs) and their composites have the advantages of large surface area, high porosity and high catalytic efficiency, which can be utilized as excellent materials for electrode modification of non-enzymatic electrochemical glucose sensors. However, MOFs and their composites still face various challenges and difficulties that limit their further commercialization. This review introduces the applications and the challenges of MOFs and their composites in non-enzymatic electrochemical glucose sensors. Finally, an outlook on the development of MOFs and their composites is also presented.

Mechanisms of interfacial catalysis and mass transfer in a flow-through electro-peroxone process

To investigate the catalytic mechanism and mass transfer efficiency in the removal of amitriptyline using an electro-peroxide process, a CuFe₂O₄-modified carbon cloth cathode was prepared and utilized in a reaction unit. The results demonstrated a remarkable efficacy of the system, achieving 91.0% amitriptyline removal, 68.3% mineralization, 41.2% mineralization current efficiency, and 0.24 kWh/m³ energy consumption within just five minutes of treatment. The study revealed that the exposed Fe atoms of the ferrite nanoparticles, with a size of 22.7 nm and 89.7% crystallinity, functioned as mediators to bind the adsorbed O atoms. The 3d_xy, 3d_xz, and 3d²_z orbitals of Fe atoms interacted with the 2p_z orbital of O atoms of H₂O₂ and O₃ to form σ and π bonds, facilitating the adsorption-activation of H₂O₂ and O₃ into hydroxyl radicals. These hydroxyl radicals (∼ 1.15 × 10¹³ mol/L) were distributed at the cathode-solution interface and rapidly consumed along the direction of liquid flow. The flow-through cathode design improved the mass transfer of aqueous O₃ and in-situ generated H₂O₂, leading to an increased yield of hydroxyl radicals, as well as the contact time and space between hydroxyl radicals and amitriptyline. Ultimately, this resulted in a higher degradation efficiency of the system.

Fabrication of polydopamine decorated carbon cloth as support material to anchor CeO2 nanoparticles for electrochemical detection of ethanol

A flexible CeO₂ nanostructured polydopamine-modified carbon cloth (CeO₂/PDA/CC) interface was fabricated via electrodeposition for ethanol detection. The fabrication method involved two consecutive electrochemical steps in which dopamine was firstly electrodeposited on carbon fibers, followed by the electrochemical growth of CeO₂ nanoparticles. The CeO₂/PDA-based electroactive interface exerts an impressive electrochemical performance on the flexible sensor due to strong synergistic effect of the PDA functionalization with more active sites. Moreover, catalytic activity of CeO₂ nanostructures anchored on highly conductive CC incorporate superior electrocatalytic performance of the fabricated interface. The designed electrochemical sensor showed a wide response to ethanol in the linear range 1 to 25 mM with a detection limit of 0.22 mM. The CeO₂/PDA/CC flexible sensor showed good anti-interference ability and excellent repeatability and reproducibility (RSD = 1.67%). The fabricated interface performed well in saliva samples with satisfactory recoveries, corroborating the viability of CeO₂/PDA/CC integrated interface for practical implementation.

Flexible quasi-solid-state zinc-ion hybrid supercapacitor based on carbon cloths displays ultrahigh areal capacitance

Over the past few years, the flexible quasi-solid-state zinc-ion hybrid supercapacitors (FQSS ZHSCs) have been found to be ideal for wearable electronics applications due to their high areal capacitance and energy density. The assembly of desirable ZHSCs devices that have promising practical applications is of high importance, whereas it is still challenging to assemble ZHSCs devices. In this study, a ZHSC that exhibited ultrahigh areal capacitance and high stability was developed by using an active carbon cloth (ACC) cathode, which could improve ionic adsorption. The as-obtained ACC cathode had an energy storage mechanism due to the electrical double-layer capacitive behavior of Zn2+, which was accompanied by the dissolution/deposition of Zn4SO4(OH)6·5H2O. The ACC//Zn@ACC ZHSC device exhibited an areal capacitance of 2437 mF cm-2 (81 F cm-3, 203 F g-1 under the mass of ACC with ∼12 mg cm-2) at 1 mA cm-2, an areal energy density of 1.354 mWh cm-2 at 1 mW cm-2, as well as high stability (with an insignificant capacitance decline after 20000 cycles), which was demonstrated to outperform the existing ZHSCs. Furthermore, the assembled flexible device still had competitive capacitance, energy density and service life when integrated into a FQSS ZHSC. When applied in practice, the device could achieve high mechanical flexibility, wearable stability and output. This study can inspire the development of the FQSS ZHSC device to satisfy the demands for wearable energy storage devices with high performance.

Interfacial engineered PANI/carbon nanotube electrode for 1.8 V ultrahigh voltage aqueous supercapacitors

Flexible three-dimensional interconnected carbon nanotubes on the carbon cloth (3D-CNTs/CC) were obtained through simple magnesium reduction reactions. According to the Nernst equation, the cell voltage based on these pure carbon electrodes without any additives could reach 1.5 V due to the higher di-hydrogen evolution over potential in neutral 3.5 M LiCl electrolytes. In order to improve the electrochemical performance of the electrodes, 3D-CNTs/CC electrodes covered with polyaniline barrier layer (3D-PANI/CNTs/CC) were prepared byin situelectropolymerization using interfacial engineering method. The assembled symmetric supercapacitors display a broadened voltage of 1.8 V, high areal capacitance of 380 mF cm^-2, outstanding areal energy density of 85.5μWh cm^-2and 84% of its initial capacitance after 20 000 charge-discharge cycles. This work demonstrated that the interface engineering strategy provides a promising way to improve the energy density of carbon-based aqueous supercapacitors by widening the voltage and boosting the capacitance simultaneously.

MoS2 nanosheets on plasma-nitrogen-doped carbon cloth for high-performance flexible supercapacitors

With the surging demand for flexible and portable electronic devices featuring high energy and power density, the development of next-generation lightweight, flexible energy storage devices is crucial. However, achieving the expected energy and power density of supercapacitors remains a great challenge. This work reports a facile plasma-enabled method for preparing supercapacitor electrodes made of MoS2 nanosheets grown on flexible and lightweight N-doped carbon cloth (NCC). The MoS2/NCC presents an outstanding specific capacitance of 3834.28 mF/cm2 at 1 mA/cm2 and energy density of 260.94 µWh/cm2 at a power density of 354.48 µW/cm2. An aqueous symmetric supercapacitor fitted with two MoS2/NCC electrodes achieved the maximum energy density of 138.12 µWh/cm2 and the highest power density of 7,417.33 µW/cm2, along with the excellent cycling stability of 83.3 % retention over 10,000 cycles. The high-performance energy storage ASSSs (all-solid-state supercapacitors) are demonstrated to power devices in both rigid and flexible operation modes. This work provides a new perspective for fabricating high-performance all-solid-state flexible supercapacitors for clean energy storage.

Innovative Variation in the Morphological Characteristics of Carbon Nanowalls Grown on a Molybdenum Disulfide Interlayer

Carbon is a material with interesting properties which exists in large quantities on Earth, so many studies involving carbon have been conducted. In particular, nano-sized carbon allotropes, referred to as carbon nanomaterials, comprise the subject of various studies currently underway. The electrical, chemical, physical properties of carbon nanowalls (CNWs) are modified by parameters such as surface density, height and thickness. These characteristics have significant effects on CNWs and can be adjusted as a growth interlayer. It was confirmed that the molybdenum disulfide (MoS₂) interlayer synthesized in this paper by radio frequency (RF) magnetron sputtering altered the morphological characteristics of the CNWs, including its shaped edge, pores diameter and density. We provide interesting results through FE-SEM, EDS and Raman analysis in this paper. Based on the Raman analysis, both the D-peak of carbon and the I_D/I_G ratio decreased. Through this study, the effect of MoS₂ on the morphological characteristics of CNWs was confirmed.

Structural Regulation of Oxygen Vacancy-Rich K0.5 Mn2 O4 Cathode by Carbon Hybridization for Enhanced Zinc-Ion Energy Storage

High-voltage manganese-based materials are considered as promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, oxygen vacancy-rich K_0.5 Mn₂ O₄ sheets were anchored uniformly onto honeycomb-like interconnected carbon nanoflakes (CNF@K_0.5 Mn₂ O₄ ) for AZIB cathode applications. In the composite, the CNFs provided excellent intergranular electron transport capability, while the oxygen vacancies enhanced the electron transport efficiency inside crystals, and the embedded K ions expanded the interlayer spacing and stabilized the layered crystal structure. A reversible specific capacity of 241 mAh g^-1 could be maintained by the composite at 0.5 A g^-1 for 400 cycles. A combination of ex-situ analytical methods and density functional theory calculations was carried out to elucidate the electrochemical mechanism of reversible zinc storage. In addition, flexible quasi-solid-state batteries of Zn//CNF@K_0.5 Mn₂ O₄ were constructed by substituting the traditional aqueous electrolyte for a quasi-solid-state gel electrolyte, which worked efficiently and exhibited high bending durability.

Life Cycle Assessment and Life Cycle Cost of an Innovative Carbon Paper Sensor for 17α-Ethinylestradiol and Comparison with the Classical Chromatographic Method

Nowadays there is a growing concern with the environment and sustainability, which means that better methods, including pollutants analysis, with less consumption of materials, organic solvents, and energy, need to be developed. Considering the almost inexistent information about the topic, the main goal of this work was to compare the environmental impacts of two analytical methods, a traditional one based on liquid chromatography with fluorescence detection and a newly developed carbon paper sensor. The selected analyte was 17α-ethinylestradiol, which is a contaminant of emergent concern in aquatic ecosystems due to its endocrine disruptor behavior. The life cycle assessment data showed that the sensor detection presents an almost negligible environmental impact when compared with the extraction step (the same for both methods) and the liquid chromatographic determination (roughly 80 times higher than with the sensor). The sensor values for all categories of damage are below 3% of the total method impacts, i.e., 1.6, 1.9, 2.4, and 2.9% for resources, climate change, human health, and ecosystem quality. The extraction represents 98.1% of the sensor environmental impacts (and 99.6% of its life cycle costing) and 38.8% of the chromatographic method. This study evidences the need of developing and applying greener analytical (detection and extraction) strategies.

Conducting Polymer-Coated Carbon Cloth Captures and Releases Extracellular Vesicles by a Rapid and Controlled Redox Process

Electrochemical techniques offer great opportunities for the capture of chemical and biological entities from complex mixtures and their subsequent release into clean buffers for analysis. Such methods are clean, robust, rapid, and compatible with a wide range of biological fluids. Here, we designed an electrochemically addressable system, based on a conducting terpolymer [P(EDOT-co-EDOTSAc-co-EDOTEG)] coated onto a carbon cloth substrate, to selectively capture and release biological entities using a simple electrochemical redox process. The conducting terpolymer composition was optimized and the terpolymer-coated carbon cloth was extensively characterized using electrochemical analysis, Raman and Fourier transform-infrared spectroscopy, water contact angle analysis, and scanning electron microscopy. The conductive terpolymer possesses a derivative of EDOT with an acetylthiomethyl moiety (EDOTSAc), which is converted into a "free" thiol that then undergoes reversible oxidation/reduction cycles at +1.0 V and -0.8 V (vs Ag/AgCl), respectively. That redox process enables electrochemical capture and on-demand release. We first demonstrated the successful electrochemical capture/release of a fluorescently labeled IgG antibody. The same capture/release procedure was then applied to release extracellular vesicles (EVs), originating from both MCF7 and SKBR3 breast cancer cell line bioreactors. EVs were captured using the substrate-conjugated HER2 antibody which was purified from commercially available trastuzumab. Capture and release of breast cancer EVs using a trastuzumab-derived HER2 antibody has not been reported before (to the best of our knowledge). A rapid (2 min) release at a low potential (-0.8 V) achieved a high release efficiency (>70%) of the captured, HER2+ve, SKBR3 EVs. The developed system and the electrochemical method are efficient and straightforward and have vast potential for the isolation and concentration of various biological targets from large volumes of biological and other (e.g., environmental) samples.

Progress in the use of organic potassium salts for the synthesis of porous carbon nanomaterials: microstructure engineering for advanced supercapacitors

Porous carbon nanomaterials (PCNs) are widely applied in energy storage devices. Traditionally, PCNs were mainly synthesized by activation and templating methods, which are time-consuming, tedious, corrosive and relatively high cost. Therefore, the development of easier and greener methods to produce PCNs is of great significance. Recently, organic potassium salts (OPSs) emerged as versatile reagents for synthesizing PCNs. The OPS-based synthesis of PCNs can avoid the use of large amounts of corrosive chemical agents. Potassium carbonate generated in situ from the decomposition of OPSs could serve as both a green activation agent and a water-removable template to produce nanopores. Potassium oxide and potassium formed at higher temperature could generate additional porosity, contributing to a highly porous architecture. The carbon-rich organic moiety could function as a carbon precursor and chemical blowing agent. This review aims to elucidate the multifunctionality of OPSs in the synthesis of PCNs and the capacitive performance of the corresponding PCNs. To this end, recent progress on the capacitive performance of PCNs synthesized from OPSs is summarized. This review provides constructive viewpoints for the cost-effective and green synthesis of PCNs with the aid of OPSs for application in supercapacitors.

2D graphdiyne: an emerging carbon material

As a new member of carbon allotropes, graphdiyne (GDY) has the characteristics of being one-atom-thick with two-dimensional layers comprising sp and sp² hybridized carbon atoms, and represents a trend in the development of carbon materials. Its unique chemical and electronic structures give GDY many unique and fascinating properties such as rich chemical bonds, highly conjugated and super-large π structures, infinitely distributed pores and high inhomogeneity of charge distribution. GDY has entered a period of rapid development, especially with the significant emergence of fundamental research and applied research achievements over the past five years. As one of the frontiers of chemistry and materials science, graphdiyne was listed in the Top 10 research areas in the 2020 Research Frontiers report and was jointly released in the Top 10 in the world by Clarivate and the Chinese Academy of Sciences. The research results have shown the great potential of GDY in the applications of energy, catalysis, environmental science, electronic devices, detectors, biomedicine and therapy, etc. Scientists are eager to explore and fully reveal the new properties, discover new scientific concepts and phenomena, discover the new conversion modes and mechanisms of GDY in photoelectricity, energy, and catalysis, etc., and build the important scientific value of new conversion devices. This review covers research on the foundation and application of GDY, such as the controlled preparation of new methods of GDY and GDY-based materials, studies on new mechanisms and properties in chemistry and physics, and the foundation and applications in energy, catalysis, photoelectric and devices.

Electronic Structure Reconfiguration of Self-Supported Polyoxometalate-Based Lithium-Ion Battery Anodes for Efficient Lithium Storage

Polyoxometalate (POM)-based materials are considered as promising candidates for lithium-ion batteries (LIBs) due to their stable and well-defined molecular structure and reversible multielectron redox properties. Currently, POM-based electrode materials suffer from high interfacial resistance and low uniformity. Herein, we reported a self-supported POM-based anode material for LIBs by electrodepositing H₃PMo₁₂O₄₀ (PMo₁₂) and aniline on carbon cloth (CC) for the first time. The as-prepared polyaniline (PANi)-PMo₁₂/CC composite exhibited an excellent reversible capacity of 1092 mA h g^-1 for 200 cycles at 1 A g^-1. Such an outstanding performance was attributed to the rapid electron transfer and Li⁺ diffusion stemming from the exposure of more active sites by the self-supported structure, the strong electrostatic interaction, and electronic structure reconfiguration between the active PMo₁₂ cluster and conductive PANi polymer. This work provides insight into the electronic structure engineering of highly efficient LIB anode materials.

High performance flexible asymmetric supercapacitor constructed by cobalt aluminum layered double hydroxide @ nickel cobalt layered double hydroxide heterostructure grown in-situ on carbon cloth

HYPOTHESIS

Three-dimensional layered layered double hydroxide (LDH) nanostructure materials grow in-situ on excellent conductive and flexible carbon cloth (CC) substrate not only reduce the ability of binders in resisting ions transfer, but also make them to be quasi-vertically arranged well on substrates without aggregation. This would result in enough electroactive sites, to obtain superior electrochemical performance.

EXPERIMENTS

A hierarchical CoAl-LDH@NiCo-LDH composite was prepared on a surface-modified carbon cloth by a simple two-step hydrothermal process. In this process, CoAl-LDH nanosheets (NSs)/CC acting as the inner core were wrapped up in NiCo-LDH nanoneedle arrays (NNAs) evenly. Also, a flexible quasi-solid-state supercapacitor device was constructed using CoAl-LDH@NiCo-LDH/CC and activated carbon (AC) as a positive electrode and a negative electrode, respectively.

FINDINGS

The CoAl-LDH@NiCo-LDH/CC developed had an excellent specific capacitance (2633.6F/g at 1 A/g) with remarkable cyclic performance (92.5% retention of its incipient over 5000 cycles at 4 A/g). The flexible quasi-solid-state supercapacitor device CoAl-LDH@NiCo-LDH/CC//AC/CC yielded a splendid energy density of 57.8 Wh/kg at a power density of 0.81 kW/kg and a brilliant power density of 16.09 kW/kg at 38.0 Wh/kg in a broad potential window of 1.55 V. Furthermore, the exceptional cyclic stability and excellent flexibility of the device show it can be applied in flexible energy storage systems.

2D Graphdiyne: A Rising Star on the Horizon of Energy Conversion

Two-dimensional (2D) graphdiyne (GDY), a rapidly rising star on the horizon of carbon materials, is a new carbon allotrope featuring sp- and sp² -cohybridized carbon atoms and 2D one-atom-thick network. Since the first successful synthesis of GDY by Professor Li's group in 2010, GDY has attached great interests from both scientific and industrial viewpoints based on its unique structure and physicochemical properties, which provides a fertile ground for applications in various fields including electrocatalysis, energy conversion, energy storage and optoelectronic devices. In this work, various potential properties of the GDY-based electrocatalysts and their recent advances in energy conversion are reviewed, including atomic catalysts, heterogeneous catalysts, and metal-free catalysts. The critical role of GDY in improving catalytic activity and stability is analyzed. The perspectives of the challenges and opportunities faced by GDY-based materials for energy conversion are also outlined.

Functionalized and tip-open carbon nanotubes for high-performance symmetric supercapacitors

Carbon nanotubes (CNTs) have been widely studied for use in supercapacitor electrodes because of their excellent conductivity, high aspect ratio, excellent mechanical properties, chemical stability, and large specific surface area. However, the electrochemical performance of CNTs is usually limited by their closed tips and fewer active sites. Therefore, a facile and efficient chemical-acid-etching method was employed to open the tips of CNTs and introduce functional groups. Different types of ions (Li⁺, Na⁺, and Mg²⁺) in aqueous electrolytes were investigated using the functionalized and tip-open CNTs (FTO-CNTs), and the Li⁺-based electrolyte has the best electrochemical performance. The areal capacitance when using FTO-CNTs as positive and negative electrodes could reach 542 mF cm^-2 and 410 mF cm^-2, respectively, at a scan rate of 10 mV s^-1, and the positive electrode reached the highest areal capacitance of 903 mF cm^-2 at a current density of 1 mA cm^-2. The symmetric supercapacitor-based FTO-CNTs electrode delivered a superior areal energy density of 39 μW h cm^-2 and an areal power density of 10.2 mW cm^-2, with remarkable cycling stability.

In Situ Reactor-Integrated Electrospray Ionization Mass Spectrometry for Heterogeneous Catalytic Reactions and Its Application in the Process Analysis of High-Pressure Liquid-Phase Lignin Depolymerization

Process analysis of heterogeneous catalytic reactions such as lignin depolymerization is essential to understand the reaction mechanism at the molecular level, but it is always challenging due to harsh conditions. Herein, we report an operando process analysis strategy by combining a microbatch reactor with high-resolution mass spectrometry (MS) via a reactor-integrated electrospray ionization (R-ESI) technique. R-ESI-MS expands the applications of traditional in situ MS to a heterogeneous and high-pressure liquid-phase system. With this strategy, we present the evolution of a series of monomers, dimers, and oligomers during lignin depolymerization under operando conditions (methanol solvent, 260 °C, ∼8 MPa), which is the first experimental elucidation of a progressive depolymerization pathway and evidence of repolymerization of active monomers. The proposed R-ESI-MS is crucial in probing depolymerization intermediates of lignin; it also provides a flexible strategy for process analysis of heterogeneous catalytic reactions under operando conditions.

Recent Development of Flexible and Stretchable Supercapacitors Using Transition Metal Compounds as Electrode Materials

Flexible and stretchable supercapacitors (FS-SCs) are promising energy storage devices for wearable electronics due to their versatile flexibility/stretchability, long cycle life, high power density, and safety. Transition metal compounds (TMCs) can deliver a high capacitance and energy density when applied as pseudocapacitive or battery-like electrode materials owing to their large theoretical capacitance and faradaic charge-storage mechanism. The recent development of TMCs (metal oxides/hydroxides, phosphides, sulfides, nitrides, and selenides) as electrode materials for FS-SCs are discussed here. First, fundamental energy-storage mechanisms of distinct TMCs, various flexible and stretchable substrates, and electrolytes for FS-SCs are presented. Then, the electrochemical performance and features of TMC-based electrodes for FS-SCs are categorically analyzed. The gravimetric, areal, and volumetric energy density of SC using TMC electrodes are summarized in Ragone plots. More importantly, several recent design strategies for achieving high-performance TMC-based electrodes are highlighted, including material composition, current collector design, nanostructure design, doping/intercalation, defect engineering, phase control, valence tuning, and surface coating. Integrated systems that combine wearable electronics with FS-SCs are introduced. Finally, a summary and outlook on TMCs as electrodes for FS-SCs are provided.

Advanced Tri-Layer Carbon Matrices with π-π Stacking Interaction for Binder-Free Lithium-Ion Storage

Enabling materials with distinct features toward achieving high-performance energy storage devices is of huge importance but highly challenging. Commercial carbon cloth (CC), because of its appealing chemical and mechanical properties, has been proven to be an excellent conductive substrate for active electrode materials. However, its performance is notably poor when directly used as an electrode in energy storage, due to its low theoretical capacity and surface area. Herein, we successfully endow the CC with enhanced storage capacity via formation of a π-π stacking interaction by integrating electrochemically activated CC (denoted CC/ACC) with biomass-derived carbon (BMDC) (denoted π-CC/ECC@BMDC). The π-CC/ECC@BMDC electrode displays excellent storage performance with a high capacity of 2.53 mAh cm^-2 under 0.2 mA cm^-2 when used as anode material for lithium ion batteries (LIBs). Due to the induction energy, the negatively charged molecules of the CC/ACC functional groups interact with the BMDC during carbonization, creating the π-π stacking interaction. Based on first-principles calculations, the structural design of the tri-layer carbon enables the movement of electrons around the π-π stacking interaction, which significantly facilitates rapid transportation of electrons, creates three-dimensional (3D) ion tunnels for fast transportation of ions, and improves the electrode's mechanical and electronic properties.

A Porphyrinic Zirconium Metal-Organic Framework for Oxygen Reduction Reaction: Tailoring the Spacing between Active-Sites through Chain-Based Inorganic Building Units

The oxygen reduction reaction (ORR) is central in carbon-neutral energy devices. While platinum group materials have shown high activities for ORR, their practical uses are hampered by concerns over deactivation, slow kinetics, exorbitant cost, and scarce nature reserve. The low cost yet high tunability of metal-organic frameworks (MOFs) provide a unique platform for tailoring their characteristic properties as new electrocatalysts. Herein, we report a new concept of design and present stable Zr-chain-based MOFs as efficient electrocatalysts for ORR. The strategy is based on using Zr-chains to promote high chemical and redox stability and, more importantly, tailor the immobilization and packing of redox active-sites at a density that is ideal to improve the reaction kinetics. The obtained new electrocatalyst, PCN-226, thereby shows high ORR activity. We further demonstrate PCN-226 as a promising electrode material for practical applications in rechargeable Zn-air batteries, with a high peak power density of 133 mW cm-2. Being one of the very few electrocatalytic MOFs for ORR, this work provides a new concept by designing chain-based structures to enrich the diversity of efficient electrocatalysts and MOFs.

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.