Hollow Carbon-Based Nanoarchitectures Based on ZIF: Inward/Outward Contraction Mechanism and Beyond.

Hollow carbon-based nanoarchitectures (HCAs) derived from zeolitic imidazolate frameworks (ZIFs), by virtue of their controllable morphology and dimension, high specific surface area and nitrogen content, richness of metal/metal compounds active sites, and hierarchical pore structure and easy exposure of active sites, have attracted great interests in many fields of applications, especially in heterogeneous catalysis, and electrochemical energy storage and conversion. Despite various approaches that have been developed to prepare ZIF-derived HCAs, the hollowing mechanism has not been clearly disclosed. Herein, a specialized overview of the recent progress of ZIF-derived HCAs is introduced to provide an insight into their preparation strategy and the corresponding hollowing mechanisms. Based on the fundamental understanding of the structural evolution of ZIF nanocrystals during the high-temperature pyrolysis process, the hollowing mechanisms of ZIF-derived HCAs are classified into four categories: i) inward contraction of core-shell template@ZIF composites or hollow ZIFs, ii) outward contraction of ZIF@shell composites, iii) special outward contraction of ZIF arrays, and iv) mechanism beyond inward/outward contraction of pure ZIF nanocrystals. Finally, an outlook on the development prospects and challenges of HCAs based on ZIF precursors, especially in terms of controlled synthesis and future electrochemical application, is further discussed.

Recent Advances of Porous Graphene: Synthesis, Functionalization, and Electrochemical Applications.

Graphene is a 2D sheet of sp2 bonded carbon atoms and tends to aggregate together, due to the strong π-π stacking and van der Waals attraction between different layers. Its unique properties such as a high specific surface area and a fast mass transport rate are severely blocked. To address these issues, various kinds of 2D holey graphene and 3D porous graphene are either self-assembled from graphene layers or fabricated using graphene related materials such as graphene oxide and reduced graphene oxide. Porous graphene not only possesses unique pore structures, but also introduces abundant exposed edges and accelerates mass transfer. The properties and applications of these porous graphenes and their composites/hybrids have been extensively studied in recent years. Herein, recent progress and achievements in synthesis and functionalization of various 2D holey graphene and 3D porous graphene are reviewed. Of special interest, electrochemical applications of porous graphene and its hybrids in the fields of electrochemical sensing, electrocatalysis, and electrochemical energy storage, are highlighted. As the closing remarks, the challenges and opportunities for the future research of porous graphene and its composites are discussed and outlined.

Research Advances of Amorphous Metal Oxides in Electrochemical Energy Storage and Conversion.

Amorphous metal oxides (AMOs) have aroused great enthusiasm across multiple energy areas over recent years due to their unique properties, such as the intrinsic isotropy, versatility in compositions, absence of grain boundaries, defect distribution, flexible nature, etc. Here, the materials engineering of AMOs is systematically reviewed in different electrochemical applications and recent advances in understanding and developing AMO-based high-performance electrodes are highlighted. Attention is focused on the important roles that AMOs play in various energy storage and conversion technologies, such as active materials in metal-ion batteries and supercapacitors as well as active catalysts in water splitting, metal-air batteries, and fuel cells. The improvements of electrochemical performance in metal-ion batteries and supercapacitors are reviewed regarding the enhancement in active sites, mechanical strength, and defect distribution of amorphous structures. Furthermore, the high electrochemical activities boosted by AMOs in various fundamental reactions are elaborated on and they are related to the electrocatalytic behaviors in water splitting, metal-air batteries, and fuel cells. The applications in electrochromism and high-conducting sensors are also briefly discussed. Finally, perspectives on the existing challenges of AMOs for electrochemical applications are proposed, together with several promising future research directions.

One Dimensional Silver-based Nanomaterials: Preparations and Electrochemical Applications.

One dimensional (1D) silver-based nanomaterials have a great potential in various fields because of their high specific surface area, high electric conductivity, optoelectronic properties, mechanical flexibility and high electro-catalytic efficiency. In this Review, the preparations of 1D silver-based nanomaterials is classified by structure composed of simple silver nanowires/rods/belts/tubes, core-shells, and hybrids. The latest applications based on 1D silver nanomaterials and their composite materials are summarized systematically including electrochemical capacitors, lithium-ion/lithium-oxygen batteries, electrochemical sensors and electrochemical catalysis. The preparation process, tailored material properties and electrochemical applications are discussed.

Facile Synthesis, Structural, Morphological and Electrochemical Properties of Bismuth Sulfide (Bi2S3) Nanostructures.

Bismuth sulfide (Bi2S3) nanowires were synthesized successfully by a facile sonochemical method from Bi(DTC)3 as a single source precursor. The structural, vibrational, morphological properties and the functional groups of the samples were confirmed by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and Raman spectroscopy techniques. The formation of pure phase of Bi2S3 and nanowires like morphology was confirmed by powder XRD and SEM analysis. The purity and elemental composition of Bi2S3 nanowires were confirmed by EDX analysis. The electrochemical properties of Catechol (CC) at the modified electrode were studied with the presence of Bi2S3 nanowires modified GCE electrode in aqueous solution with different scan rate and concentration. A novel method for determination of catechol using cyclic voltammetry (CV) was investigated. The homogeneous rate constants were estimated by comparing the experimental CV responses with the digital simulated results.

Research Progress on the Preparation of Manganese Dioxide Nanomaterials and Their Electrochemical Applications.

Manganese dioxide (MnO2) nanomaterials have shown excellent performance in catalytic degradation and other fields because of their low density and great specific surface area, as well as their tunable chemical characteristics. However, the methods used to synthesize MnO2 nanomaterials greatly affect their structures and properties. Therefore, the present work systematically illustrates common synthetic routes and their advantages and disadvantages, as well as examining research progress relating to electrochemical applications. In contrast to previous reviews, this review summarizes approaches for preparing MnO2 nanoparticles and describes their respective merits, demerits, and limitations. The aim is to help readers better select appropriate preparation methods for MnO2 nanomaterials and translate research results into practical applications. Finally, we also point out that despite the significant progress that has been made in the development of MnO2 nanomaterials for electrochemical applications, the related research remains in the early stages, and the focus of future research should be placed on the development of green synthesis methods, as well as the composition and modification of MnO2 nanoparticles with other materials.

Stainless Steel Mesh in Electrochemistry: Comprehensive Applications and Future Prospects.

Stainless steel mesh (SSM) has emerged as a cornerstone in electrochemical applications owing to its exemplary versatility, electrical conductivity, mechanical robustness, and corrosion resistance. This state-of-the-art review delves into the diverse roles of SSM across a spectrum of electrochemical domains, including energy conversion and storage devices, water treatment technologies, electrochemical sensors, and catalysis. We meticulously explore its deployment in supercapacitors, batteries, and fuel cells, highlighting its utility as a current collector, electrode, and separator. The review further discusses the critical significance of SSM in water treatment processes, emphasizing its efficacy in supporting membranes and facilitating electrocoagulation, as well as its novel uses in electrochemical sensing and catalysis, which include electrosynthesis and bioelectrochemistry. Each section delineates the recent advancements, identifies the inherent challenges, and suggests future directions for leveraging SSM in electrochemical technologies. This comprehensive review showcases the current state of knowledge and articulates the novel integration of SSM with emerging materials and technologies, thereby establishing a new paradigm for sustainable and efficient electrochemical applications. Through critical analysis and insightful recommendations, this review positions itself as a seminal contribution, paving the way for researchers and practitioners to harness the full potential of SSM in advancing the electrochemistry frontiers.

Current insights and future prospects of graphene aerogel-enhanced supercapacitors: A systematic review.

Supercapacitors present a compelling alternative to conventional batteries, offering rapid energy storage and high power density. Despite their advantages, they typically fall short in energy density compared to traditional batteries, primarily due to limitations in electrode materials. Graphene Aerogels (GA) have emerged as a promising solution to enhance supercapacitor performance because of their unique properties, such as high surface area and excellent conductivity. This systematic review provides a comprehensive analysis of recent advancements in GA technology, focusing on their synthesis methods and applications in supercapacitors. It highlights significant improvements that GA can bring to Electric Double-Layer Capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors. Additionally, the review explores GA's potential for enhancing electric generators and integrating into flexible, wearable technologies. Future research directions are emphasised, particularly regarding GA's potential applications in waste management and environmental protection. The review was conducted through a thorough literature search, prioritising peer-reviewed sources related to GA synthesis and supercapacitor applications. Methodological quality and potential biases of the included studies were assessed using principles similar to the Cochrane Risk of Bias tool. Thematic analysis was employed to synthesise findings and identify key trends and challenges. Limitations such as potential biases and methodological variations are discussed. Overall, this review highlights the technological prospects of GA and provides guidance for future research in supercapacitor development and applications.

Tragia involucrata Leaf-Mediated ZnO NPs: Biomedical Applications, Ointment Formulation and Electrochemical Studies.

Zinc oxide (ZnO) NPs, owing to their broad biomedical applications, have recently attracted the scientific community with incredible interest as therapeutic agents. So, the present study aims at preparation of ZnO NPs, using Tragia involucrata leaf extract and exploring their capability as antioxidant, anticancer and anti-inflammatory agents. Besides, the ointment formulation and electrochemical studies were also carried out in this work. The antioxidant activity of the synthesized ZnO NPs was evaluated using DPPH assay method and the results clearly showed higher inhibition of about 70% and lower inhibition of about 14% for 100 µg/ml and 25 µg/ml concentrations, respectively. The cytotoxic effects of ZnO NPs were evaluated against human cancer cell lines such as A549 (lungs), HeLa (cervical), HeP-2 (laryngeal) and MCF-7 (breast). The outcome of this investigation confirmed the effectiveness of the synthesized NPs against HeP-2 even at the lowest concentration. The anti-inflammatory activity was measured by the inhibition of protein denaturation assay. A higher inhibition of about 54% was noticed at the concentration of 100 µg/ml. In the case of the ointment formulation study, the pastes prepared using the biosynthesized ZnO NPs and commercially available ZnO powder were compared and evaluated using the parameters such as pH, spreadability, moisture content, extrudability, foamability and physical examinations. As it has been noticed that all the observed parameters were matching well with those of the commercially available ZnO powder, ZnO NPs, synthesized using Tragia involucrata, may be suggested for the clinical trials. Cyclic voltammetry was used to measure the specific capacitance of the synthesized ZnO NPs for different scan rates. The results of this study showed the gradual decrease in specific capacitance value for the corresponding increase in scan rates. Therefore, the results of present study indicated that ZnO NPs prepared using Tragia involucrata leaves were found to be effective for all the above chosen applications and hence, have multifunctional capacity.

Selected Kraft lignin fractions as precursor for carbon foam: Structure-performance correlation and electrochemical applications.

The rapid exhaustion of fossil fuels brings to the fore the need to search for energy efficient strategies. The conversion of lignin into advanced functional carbon-based materials is considered one of the most promising solutions for environmental protection and the use of renewable resources. This study analyzed the structure-performance correlation of carbon foams (CF) when lignin-phenol-formaldehyde (LPF) resins produced with different fractions of kraft lignin (KL) were employed as carbon source, and polyurethane foam (PU) as sacrificial mold. The lignin fractions employed were KL, fraction of KL insoluble in ethyl acetate (LFIns) and fraction of KL soluble in ethyl acetate (LFSol). The produced CFs were characterized by thermogravimetric analysis (TGA), X-ray diffractometry (XRD), Raman spectroscopy, 2D HSQC Nuclear magnetic resonance (NMR) analysis, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and electrochemical measurements. The results showed that when LFSol was employed as a partial substitute for phenol in LPF resin synthesis, the final performance of the produced CF was infinitely higher. The improved solubility parameters of LFSol along with the higher S/G ratio and ß-O-4/α-OH content after fractionation were the key to produce CF with better carbon yields (54 %). The electrochemical measurements showed that LFSol presented the highest current density (2.11 × 10-4 mA.cm-2) and the lowest value of resistance to charge transfer (0.26 KΩ) in relation to the other samples, indicating that the process of electron transfer was faster in the sensor produced with LFSol. LFSol's potential for application as an electrochemical sensor was tested as a proof of concept and demonstrated excellent selectivity for the detection of hydroquinone in water.

Understanding the Impedance of Mesoporous Oxides: Reliable Determination of the Material-Specific Conductivity.

The unique architecture of ordered mesoporous oxides makes them a promising class of materials for various electrochemical applications, such as gas sensing or energy storage and conversion. The high accessibility of the internal surface allows tailoring of their electrochemical properties, e.g., by adjusting the pore size or surface functionalization, resulting in superior device performance compared to nanoparticles or disordered mesoporous counterparts. However, optimization of the mesoporous architecture requires reliable electrochemical characterization of the system. Unfortunately, the interplay between nanocrystalline grains, grain boundaries, and the open pore framework hinders a simple estimation of material-specific transport quantities by using impedance spectroscopy. Here, we use a 3D electric network model to elucidate the impact of the pore structure on the electrical transport properties of mesoporous thin films. It is demonstrated that the impedance response is dominated only by the geometric current constriction effect arising from the regular pore network. Estimating the effective conductivity from the total resistance and the electrode geometry, thus, differs by more than 1 order of magnitude from the material-specific conductivity of the solid mesoporous framework. A detailed analysis of computed impedances for varying pore size allows for the correlation of the effective conductivity with the material-specific conductivity. We derive an empirical expression that accounts for the porous structure of the thin films and allows a reliable determination of the material-specific conductivity with an error of less than 8%.

Hierarchical Design in Nanoporous Metals.

Hierarchically porous metals possess intriguing high accessibility of matter molecules and unique continuous metallic frameworks, as well as a high level of exposed active atoms. High rates of diffusion and fast energy transfer have been important and challenging goals of hierarchical design and porosity control with nanostructured metals. This review aims to summarize recent important progress toward the development of hierarchically porous metals, with special emphasis on synthetic strategies, hierarchical design in structure-function and corresponding applications. The current challenges and future prospects in this field are also discussed.

Controlled Porosity in Ferroelectric BaTiO3 Photoanodes.

The use of ferroelectric polarization to promote electron-hole separation has emerged as a promising strategy to improve photocatalytic activity. Although ferroelectric thin films with planar geometry have been largely studied, nanostructured and porous ferroelectric thin films have not been commonly used in photo-electrocatalysis. The inclusion of porosity in ferroelectric thin films would enhance the surface area and reactivity, leading to a potential improvement of the photoelectrochemical (PEC) performance. Herein, the preparation of porous barium titanate (pBTO) thin films by a soft template-assisted sol-gel method is reported, and the control of porosity using different organic/inorganic ratios is verified by the combination of scanning electron microscopy and ellipsometry techniques. Using piezoresponse force microscopy, the switching of ferroelectric domains in pBTO thin films is observed, confirming that the ferroelectric polarization is still retained in the porous structures. In addition, the presence of porosity in pBTO thin films leads to a clear improvement of the PEC response. By electrochemical poling, we also demonstrated the tuning of the PEC performance of pBTO thin films via ferroelectric polarization. Our work offers a simple and low-cost approach to control the morphology optimization of ferroelectric thin films, which could open up the development of materials with great potential for PEC applications.

Nanostructure Engineering of Graphitic Carbon Nitride for Electrochemical Applications.

Graphitic carbon nitride with ordered two-dimensional structure displays multiple properties, including tunable structure, suitable bandgap, high stability, and facile synthesis. Many achievements on this material have been made in photocatalysis, but the advantages have not yet been fully explored in electrochemical fields. The bulk structure with low conductivity impedes charge-transfer kinetics during electrochemical processes. Excessive nitrogen content leads to insufficient charge transfer, while bulk structures produce tortuous channels for mass transport. Some attempts have been made to address these issues by nanostructure engineering, such as ultrathin structure design, heterogeneous composition, defect engineering, and morphology control. These structure-engineered nanomaterials have been successfully applied in electrochemical fields, including ionic actuators, flexible supercapacitors, lithium-ion batteries, and electrochemical sensors. Herein, a timely review on the latest advances in graphitic carbon nitride through various engineering strategies for electrochemical applications has been summarized. A perspective on critical challenges and future research directions is highlighted for graphitic carbon nitride in electrochemistry on the basis of existing research works and our experimental experience.

Covalent Organic Frameworks: Emerging Organic Solid Materials for Energy and Electrochemical Applications.

Covalent organic frameworks (COFs), materials constructed from organic building blocks joined by robust covalent bonds, have emerged as attractive materials in the context of electrochemical applications because of their high, intrinsic porosities and crystalline frameworks, as well as their ability to be tuned across two- and three-dimensions by the judicious selection of building blocks. Because of the recent and rapid development of this field, we have summarized COFs employed for electrochemical applications, such as batteries and capacitors, water splitting, solar cells, and sensors, with an emphasis on the structural design and resulting performance of the targeted electrochemical system. Overall, we anticipate this review will stimulate the design and synthesis of the next generation of COFs for use in electrochemical applications and beyond.

New Organic Electrode Materials for Ultrafast Electrochemical Energy Storage.

Organic materials are both environmentally and economically attractive as potential electrode candidates. This Research News reports on a new class of stable and electrically conductive organic electrodes based on metal porphyrins with functional groups that are capable of electrochemical polymerization, rendering the materials promising for electrochemical applications. Their structural flexibility and the unique highly conjugated macrocyclic structure allows the produced organic electrodes to act as both cathode and anode materials giving access to fast charging as well as high cycling stability. The extreme thermal and chemical stability of the porphyrin-based organic electrodes and their chemical versatility suggest an important role for these molecular systems in the further development of novel electrochemical energy storage applications.

Engineering glucose oxidase for bioelectrochemical applications.

There is still a growing interest in developing glucose sensors using glucose oxidase. Since 2012, over 1000 papers are published every year, while efficient commercial sensors exist on the market. Among those glucose sensors, few have been thought and well-engineered and do not solve the problems associated with glucose oxidase; among which the O2 sensitivity of the enzyme or the competition between O2 and redox mediators for GOx's electrons. Enzyme engineering has been employed to solve those issues but screening GOx in homogeneous solution with O2 as an electron acceptor is not suitable. Very few reports describe the specific reengineering of GOx for electrochemical applications and are the subject of this review. It starts with a brief presentation of glucose oxidase and presents the recent progress in glucose oxidase reengineering by highlighting the kind of engineering/mutations performed to increase its electron transfer rate to electrode surfaces and, to decrease its O2 sensitivity. In addition, the review highlights the need to develop new screening methods involving electrochemical probing, essential to develop the next generation of glucose sensors; specific to glucose, O2 independent, biocompatible and stable over 2 weeks.