Synthesis and Electrochemical Study of Three-Dimensional Graphene-Based Nanomaterials for Energy Applications

Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Porous Flow Field for Next-Generation Proton Exchange Membrane Fuel Cells: Materials, Characterization, Design, and Challenges

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L^-1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization.

Electrochemical Exfoliation of Graphite to Graphene-Based Nanomaterials

Here, we report on a new automated electrochemical process for the production of graphene oxide (GO) from graphite though electrochemical exfoliation. The effects of the electrolyte and applied voltage were investigated and optimized. The morphology, structure and composition of the electrochemically exfoliated GO (EGO) were probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy and Raman spectroscopy. Important metrics such as the oxygen content (25.3 at.%), defect density (I_D/I_G = 0.85) and number of layers of the formed EGO were determined. The EGO was also compared with the GO prepared using the traditional chemical method, demonstrating the effectiveness of the automated electrochemical process. The electrochemical properties of the EGO, CGO and other carbon-based materials were further investigated and compared. The automated electrochemical exfoliation of natural graphite powder demonstrated in the present study does not require any binders; it is facile, cost-effective and easy to scale up for a large-scale production of graphene-based nanomaterials for various applications.

Recent advances of carbon-based nanomaterials (CBNMs) for wastewater treatment: Synthesis and application

Carbon-based nanomaterials (CBNMs) have attracted significant alert due to the affluent science underpinning their implementations associated with a novel mixture of high aspect proportions, greater thermal and electrical performance, outstanding optical features, and high exterior area. CBNMs not only bear assurance in a broad range of implementations in medication, nano and microelectronics, and ecological remedies but may also be utilized in practical laboratory determinations. More specifically, CBNMs perform as an outstanding adsorbent in terminating heavy metal ions (HMI) from wastewater. There is presently a deficiency of powerful threat inspection instruments owing to their complex detection and related deficit in the health risk database. Therefore, our present review concentrates on spreading CBNMs to release pollutants from wastewater. The article wraps the effect of these contaminants and photocatalytic strategies towards treating these mixtures in wastewater, along with their restrictions and challenges, convincing resolutions, and possibilities of these approaches.

Recent Developments of Transition Metal Compounds-Carbon Hybrid Electrodes for High Energy/Power Supercapacitors

Due to their rapid power delivery, fast charging, and long cycle life, supercapacitors have become an important energy storage technology recently. However, to meet the continuously increasing demands in the fields of portable electronics, transportation, and future robotic technologies, supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged. Transition metal compounds (TMCs) possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors. However, the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process, which greatly impede their large-scale applications. Most recently, the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges. Herein, we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies, including conductive carbon skeleton, interface engineering, and electronic structure. Furthermore, the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.

Enhanced Supercapacitor Performance and Electromagnetic Interference Shielding Effectiveness of CuS Quantum Dots Grown on Reduced Graphene Oxide Sheets

This study is focused on the preparation of the CuS/RGO nanocomposite via the hydrothermal method using GO and Cu-DTO complex as precursors. X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopy study revealed the formation of the CuS/RGO nanocomposite with improved crystallinity, defective nanostructure, and the presence of the residual functional group in the RGO sheet. The morphological study displayed the transformation of CuS from nanowire to quantum dots with the incorporation of RGO. The galvanostatic charge/discharge curve showed that the CuS/RGO nanocomposite (12 wt % Cu-DTO complex) has tremendous and outperforming specific capacitance of 3058 F g-1 at 1 A g-1 current density with moderate cycling stability (∼60.3% after 1000 cycles at 10 A g-1). The as-prepared nanocomposite revealed excellent improvement in specific capacitance, cycling stability, Warburg impedance, and interfacial charge transfer resistance compared to neat CuS. The fabricated nanocomposites were also investigated for their bulk DC electrical conductivity and EMI shielding ability. It was observed that the CuS/RGO nanocomposite (9 wt % Cu-DTO) exhibited a total electromagnetic shielding efficiency of 64 dB at 2.3 GHz following absorption as a dominant shielding mechanism. Such a performance is ascribed to the presence of interconnected networks and synergistic effects.

Bioelectrocatalysis of Hemoglobin on Electrodeposited Ag Nanoflowers toward H2O2 Detection

Hydrogen peroxide (H2O2) is a partially reduced metabolite of oxygen that exerts a diverse array of physiological and pathological activities in living organisms. Therefore, the accurate quantitative determination of H2O2 is crucial in clinical diagnostics, the food industry, and environmental monitoring. Herein we report the electrosynthesis of silver nanoflowers (AgNFs) on indium tin oxide (ITO) electrodes for direct electron transfer of hemoglobin (Hb) toward the selective quantification of H2O2. After well-ordered and fully-grown AgNFs were created on an ITO substrate by electrodeposition, their morphological and optical properties were analyzed with scanning electron microscopy and UV-Vis spectroscopy. Hb was immobilized on 3-mercaptopropionic acid-coated AgNFs through carbodiimide cross-linking to form an Hb/AgNF/ITO biosensor. Electrochemical measurement and analysis demonstrated that Hb retained its direct electron transfer and electrocatalytic properties and acted as a H2O2 sensor with a detection limit of 0.12 µM and a linear detection range of 0.2 to 3.4 mM in phosphate-buffered saline (PBS). The sensitivity, detection limit, and detection range of the Hb/AgNF/ITO biosensor toward detection H2O2 in human serum was also found to be 0.730 mA mM-1 cm-2, 90 µM, and 0.2 to 2.6 mM, indicating the clinical application for the H2O2 detection of the Hb/AgNF/ITO biosensor. Moreover, interference experiments revealed that the Hb/AgNF/ITO sensor displayed excellent selectivity for H2O2.

First-principles investigation on the bonding mechanisms of two-dimensional carbon materials on the transition metals surfaces

Understanding the bonding mechanisms between carbon and metal atoms are crucial for experimental preparations of low-dimensional carbon materials and metal/low-dimensional carbon composites. In this work, various bonding modes are summarized through a systematical study on the adsorptions of graphene and graphyne on surfaces of typical transition metals. If a carbon atom is adjacent to a transition metal atom, the C-p_z electron may form a covalent bond with a s or a d electron of the transition metal atom. When a metal atom lies below two carbon atoms of graphene or graphyne, two new covalent bonds may be formed between the metal atom and the two carbon atoms by two C-p_z electrons with two d or two sd-hybridized orbital electrons of the transition metal atom. Specially, the two covalent bonds are almost identical by two sd-hybridized orbital electrons, but the two bonds should show significant differences by two d-orbital electrons. Three covalent bonds formed between three carbon atoms and one sd²-hybridized Ti atom are observed on the graphyne/Ti (0001) interface. In addition to the existing sp and sp² hybridizations, the carbon atom may show the sp³ hybridization after graphyne adsorbs on some metals. These research results are obtained through a comprehensive analysis of the adsorption configuration, the differential charge density, and the projected of states from the first-principles calculations in the present study.

Except for the existing sp and sp² hybridizations, the carbon shows the sp³ hybridization after graphyne adsorbs on Ti surface.