Carbon Trends最新文献

Increasing graphite demand for energy storage applications creates the need to make graphite using precursors and processes that are affordable and friendly to the environment. Non-graphitizing precursors such as biomass or polymers are known for their low cost and sustainability; therefore, graphitizing them will be an accomplishment. In this work, a process of converting a non-graphitizing precursor, phenolic resin novolac (N), into a graphitic carbon is presented. This was achieved by the addition of five additives categorized as graphene oxide (GO) and its derivatives with varied oxygen concentrations. The hypothesis is that the additives act as templates that promote matrix aromatic alignment to their basal planes during carbonization (physical templating) in addition to forming radical sites that bond to the decomposing matrix (chemical templating). Results showed that the addition of reduced graphene oxide (RGO) additives of approximately 15.4 at.(%) oxygen content to the novolac matrix (RGO-N) show the best graphitic quality. In contrast, the addition of GO additive of twice or more oxygen content ≥ 30.8 at.(%) to the novolac matrix (GO-N) led to poor graphitic quality. This suggests that there is an optimum amount of oxygen content in GO additives needed to induce graphitization of the novolac matrix.

Although heteroatom doping is an effective method to improve the capacity of hard carbon (HC) anodes in Na-ion batteries (NIBs), the complicated structure of HC leads to uncertainty when understanding the effects of heteroatom doping on sodium storage. This study shows the effects of phosphorus and sulfur doping to HC on sodium storage using solid-state NMR to improve the capacity of HC prepared by the carbonization of resorcinol formaldehyde (RF) resin at 1100 °C. Heteroatom doping increased the battery capacity of the HC, especially the plateau capacity, but the interlayer distance of the carbon layers in the HC did not expand considerably. ²³Na solid-state NMR revealed that heteroatom doping facilitates the formation of quasi-metallic sodium clusters, thereby contributing to the plateau capacity increase. The metallicity of the sodium clusters in heteroatom-doped HC samples was controlled by the amount of doped-phosphorous. XPS and ³¹P NMR detected various phosphorus sites such as phosphine and phosphine oxide in the carbon structure.

Increasing energy storage demands, and the reducing device size have led to the development of high surface area nanoporous materials. However, the energy storage in such materials do not typically scale as expected according to the increase in the surface area. This is because of another capacitance that appears in series with the electric double-layer capacitors used for energy storage. This capacitance is termed quantum capacitance, which is although present in all materials but becomes considerable in value for materials with low density of electronic states. The quantum capacitance and its effects can greatly enhance our understanding of the double-layer capacitance. In this review, we present the understanding built behind quantum capacitance based on some of the some recent work elucidating the vastness of the area that can be explored.

To accelerate the implementation of zero-emission power installations based on proton-exchange membrane fuel cells, it is necessary to maximize the power characteristics of these devices. For this purpose, we have obtained and tested a new N-doped carbon support and a synthesized Pt/C catalyst based on it with a platinum loading of about 37.3 %. A comparison of the degradation resistance of the initial support and the N-doped one has shown greater stability of the latter. At the same time, Raman spectroscopy has confirmed the presence of the C–N bond, which indicates the successful doping of carbon with nitrogen. The resulting Pt/C catalyst based on an N-doped support is characterized by a substantially narrow size dispersion and an ultra-small nanoparticle size of about 2.6 nm. The high-angle annular dark-field scanning transmission electron microscopy images of the synthesized catalyst have confirmed the presence of individual platinum atoms/clusters uniformly distributed over the surface of the support, and their presence is due to nitrogen embedded into the carbon structure. This material is characterized by a 50 m² g_Pt^-1 larger electrochemically active surface area and a 227 A g_Pt^-1 greater mass activity compared to the commercial JM40 analog (40 % platinum loading). Meanwhile, the electrochemical parameters remaining after the accelerated stress testing are almost 2 times higher than those of JM40. And the power characteristics in the membrane electrode assembly for the catalyst synthesized by the facile one-pot synthesis method are 13 % (575 mW cm^-2) higher than those of the commercial analog (500 mW cm^-2). The Pt/C catalyst obtained during the research is deemed promising for commercial use in proton-exchange membrane fuel cells.

Pressurized carbonization is known to improve carbon content and create textural changes in resultant carbon compared to conventional (atmospheric) carbonization. However, further studies investigating the impact of these carbonization methods on the graphitic quality of the carbon precursors have not been explored extensively. This study investigates the influence of carbonization methods on the graphitization behavior of soft and hard carbons using a three-model system: phenolic resole (hard carbon), polyvinyl chloride (PVC) (soft carbon), and a 50:50 blend of resole and PVC. Carbonization was conducted under autogenic pressure (AGP) and atmospheric pressure (APP) at 500 °C for 5 h, followed by high-temperature treatment at varying temperatures. Various techniques, including X-ray diffraction and Raman spectroscopy showed hard carbon precursors exhibited improved properties under AGP carbonization such as larger crystallite size, sharp crystalline peaks, lower I_D/I_G ratio, and narrow G-full width half-maximum, an indication of improved crystallinity by lowering amorphous phase at high temperature. For soft carbon precursors, the method of carbonization did not impact the graphitization level. The most significant finding was the enhanced crystalline nature observed in hard carbon under AGP conditions, without the need for any catalyst. It shows the influence of pressure on improving the crystallinity of hard carbon precursors.

Electrocatalytic carbon dioxide (CO₂) reduction has emerged as a promising approach for converting CO₂ into value-added products and mitigating greenhouse gas emissions. Layered double hydroxides (LDHs) and metal-organic frameworks (MOFs) have attracted significant attention as potential electrocatalysts for CO₂ reduction due to their unique structural properties and tunable chemical compositions. In this review, we provide a comprehensive overview of recent advances in the utilization of LDHs and MOFs as electrocatalysts for CO₂ reduction. Scrutiny on various catalysts, along with their general design ways for CO₂ reduction is presented. This review will provide insight into the up-to-date research progress in MOF-based materials for CO₂ conversion. Furthermore, we highlight opportunities in this field and propose future research directions aimed at optimizing the performance of LDHs and MOFs for CO₂ reduction applications.

The demand for suitable electrode materials for energy storage devices, driven by increasing energy needs and environmental concerns, has led to the investigation of green synthesis methods. In this study, a composite material (rGO@NCQDs) comprising nitrogen-doped carbon quantum dots (NCQDs) derived from Moosa balbeesiaana peels and reduced graphene oxide (rGO) was synthesized via hydrothermal methods to evaluate its photophysical properties and electrochemical performance for supercapacitors applications. Additionally, the electrochemical behavior of rGONCQDs combined with Vanadium pentoxide (V₂O₅) was explored.

Characterization techniques including FTIR spectroscopy revealed typical carbon-based material features in rGO-decorated NCQDs, and rGONCQDs@V₂O₅ composite. SEM analysis illustrated distinctive surface structures (mushroom-shaped for rGO@NCQDs and flowered-shaped for rGONCQDs@V2O5), while XRD confirmed crystalline structures with specific sizes.

Photophysical investigations demonstrated significant Solvatochromic shifts and strong solute-solvent interactions in the composites. Electrochemical studies, including cyclic Voltammetry and Galvanostatic measurements, exhibited promising performance metrics. Specifically, rGO@NCQDs demonstrated a specific capacitance of 134.68 Fg⁻¹ with excellent retention over 5000 charge-discharge cycles. In contrast, rGONCQDs@V₂O₅ exhibited a maximum specific capacitance of 562.62 Fg⁻¹ at a scan rate of 10 mVs⁻¹ and exceptional cycle stability (96 % retention over 5000 cycles).

These findings highlight the potential of the synthesized composites as efficient electrode materials for supercapacitors, offering enhanced electrochemical performance and stability. The study underscores the importance of green synthesis approaches in developing functional materials for sustainable energy storage applications.

This study systematically investigated the stable configurations and oxygen reduction reaction (ORR) catalytic activity of PN co-doped graphene using first-principles methods. We found that PN co-doped graphene substrates are generally highly stable. The adsorption energy of adsorbates is linearly positively correlated with the number of electrons obtained from the substrate. The P atoms serve as catalytic activity sites, the co-doping of N significantly enhances the adsorption energies of intermediate species in the ORR process, facilitating the direct dissociation of O2 and O2H. The solvation effect has a non-negligible impact on the adsorption energy of adsorbates, especially for O2. Due to the excessive adsorption of O, it poisons and inhibits the catalytic activity of P active sites for ORR. However, after O adsorption, the C atoms neighboring the PN impurity atoms in the P-Nn-Gra (n=2,3) substrates exhibit better catalytic activity than that of graphene doped with P/N alone. The P-Nn-defect-Gra (n=2,3,4) substrates are potential catalysts with good HER catalytic activity.

Carbon black (CB) has wide range of industrial applications, including in the manufacturing of automobile tires, rubber products, inks, and plastics. To improve the properties of the target products and establish recycling systems, it must be fully characterized. However, characterization of CB is challenging owing to its structural complexity and the limitation of conventionally used experimental techniques, especially for surface structures at the nanoscale. In this study, we characterized the surface structures of two commercial CB via atomic force and scanning tunneling microscopy. Analysis of well-dispersed aggregates on atomically flat solid surfaces revealed primary particles of diverse sizes. The particle surfaces lacked edges, grooves, and steps that should be observed between stacked graphene sheets, which contradicts the widely accepted crystallite model. Observed images suggest that the graphene sheets exhibit a size distribution, inferring that multiple non-uniformly sized small graphene sheets are stacked turbostratically, with each sheet displaying a localized curvature rather than the ideal planar form. Varying size of sheets and curvature indicate the presence of a decent number of edges terminated with hydrogen and oxygen-containing functional groups. This interpretation was corroborated by conventional spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and infrared absorption spectroscopy.

Carbon-carbon composite manufactured by deposition of pyrocarbon (PyC) through chemical vapor infiltration (CVI) has the key issue of being process parametric sensitive which necessitates the detailed study of the effect of process parameters on the rate of PyC deposition. Conventional method of studying the parametric effect by changing one variable at a time keeping the other variables constant has a limitation of more number of experiments and missing the interaction effect among the variables. Here, the effect of process parameters including temperature, pressure, methane gas flow rate, and nitrogen gas flow rate on the mass gain and PyC deposition was studied by Taguchi method, a statistical optimization method, which has the advantage of very few experiments performed at specific pairs of process parameters only. The experiments were performed at three levels of the process parameters. Carbon-Carbon composite material is processed through the CVI process where PyC was deposited on porous carbon fiber preforms at various process conditions as per the Taguchi method. The impact of gas residence time, Reynolds number, Prandtl number, and Peclet number were also investigated. It was observed that the CVI process parameters significantly affect the rate of PyC deposition. Optimized CVI process parameters are essential for achieving a high rate of PyC deposition to reduce the processing time. The findings have revealed that a higher PyC deposition rate arises under high temperatures, pressure, methane gas flow rate, and optimal nitrogen gas flow rate. The effect of the critical interaction of the CVI process parameters on the rate of PyC deposition was also obtained. Based on the experimental studies, process guidelines are proposed for the densification of carbon fibers preform to realize C/C composite products.