Carbon Sites Research Articles

An Unprecedented CeO2/C Non-Noble Metal Electrocatalyst for Direct Ascorbic Acid Fuel Cells.

Direct ascorbic acid fuel cells (DAAFCs) employ biocompatible ascorbic acid (AA) as fuel, allowing convenient storage, transportation, and fueling as well as avoiding fuel crossover. The AA oxidation reaction (AAOR) largely governs the performance of DAAFCs. However, AAOR electrocatalysts currently have low activity, and state-of-the-art ones are limited to carbon black. Herein, we report the synthesis of an unprecedented AAOR electrocatalyst comprising 3.9 ± 1.1 nm CeO2 nanoparticles evenly distributed on carbon black simply by the wet chemical precipitation of Ce(OH)3 and a subsequent heat treatment. The resultant CeO2/C shows a remarkable AAOR activity with a peak current density of 13.1 mA cm-2, which is 1.7 times of that of carbon black (7.67 mA cm-2). According to X-ray photoelectron spectroscopy (XPS), the surface Ce3+ of CeO2 appears to contribute to the AAOR activity. Furthermore, our density functional theory (DFT) calculation reveals that that the proton of the hydroxyl group of AA can easily migrate to the bridging O sites of CeO2, resulting in a faster AAOR with respect to the pristine carbon, -COOH, and -C=O sites of carbon. After an i-t test, CeO2/C loses 17.8% of its initial current density, which is much superior to that of carbon black. CeO2 can capture the electrons generated by the AAOR to protect the -COOH and -C=O sites from being reduced. Finally, DAAFCs fabricated with CeO2/C exhibit a remarkable power density of 41.3 mW cm-2, which is the highest among proton-exchange-membrane-based DAAFCs in the literature.

Encapsulation of sulfur in MoS2-modified metal-organic framework-derived N, O-codoped carbon host for sodium–sulfur batteries

Room-temperature sodium–sulfur batteries (RT Na-S) are promising energy storage systems with high energy densities and low costs. Nevertheless, drawbacks, including the limited cycle life and sluggish redox kinetics of sodium polysulfides, hinder their implementation. Herein, a heterostructure of MoS2 nanosheets coated on a metal–organic framework (MOF)-derived N, O-codoped flower-like carbon matrix (NOC) was designed as a sulfur host for advanced RT Na-S batteries. The NOC@MoS2 hierarchical host provided a sufficient space to guarantee a high sulfur loading and confinement for the volume expansion of sulfur during the charge/discharge process. According to first-principle calculations, the NOC@MoS2 composite exhibited metallic conductivity because electronic states crossed the Fermi level, which indicates that the introduction of NOC significantly improved the electronic conductivity of MoS2. Furthermore, electron transfer from MoS2 to the O-doped carbon sites was observed owing to the strong electronegativity of O, which can effectively increase the Lewis acidity of MoS2 and weaken the sodium–sulfur bonds in sodium polysulfides after adsorption on the cathode, leading to reductions in the Na2S dissociation energy barrier and Gibbs free energy for the rate-limiting step of the sulfur reduction process. Therefore, with the synthetic effects of MoS2 and N, O-codoped carbon, the obtained cathode exhibited a superior electrochemical performance.

Rational design of vitamin C/defective carbon van der Waals heterostructure for enhanced activity, durability and storage stability toward oxygen reduction reaction

Metal-free defective carbon materials with abundant active sites have been widely studied as low-cost and efficient oxygen reduction reaction (ORR) electrocatalysts in metal-air batteries. However, the active sites in defective carbon are easily subjected to serious oxidation or hydroxylation during ORR or storage, leading to rapid degradation of activity. Herein, we design a van der Waals heterostructure comprised of vitamin C (VC) and defective carbon (DC) to not only boost the activity but also enhance the durability and storage stability of the DC-VC electrocatalyst. The formation of VC van der Waals between DC and VC is demonstrated to be an effective strategy to protect the defect active sites from oxidation and hydroxylation degradation, thus significantly enhancing the electrochemical durability and storage anti-aging performance. Moreover, the DC-VC van der Waals can reduce the reaction energy barrier to facilitate the ORR. These findings are also confirmed by operando Fourier transform infrared spectroscopy and density functional theory calculations. It is necessary to mention that the preparation of this DC-VC electrocatalyst can be scaled up, and the ORR performance of the largely produced electrocatalyst is demonstrated to be very consistent. Furthermore, the DC-VC-based aluminum-air batteries display very competitive power density with good performance maintenance.

Revisiting energy transition projects future with "coal-to-gas" energy projects: assessing through life-cycle project cost method.

This research aims to evaluate the life-cycle project costs associated with "coal-to-gas" energy transition projects in the context of the present energy environment. Determining the possible role of such initiatives in attaining a sustainable and economical energy future is at the heart of the problem statement. Four major coal seam gas (CSG) projects have affected the local population in China. The study applied structural equation modeling (SEM) and quantile process estimation (QPE) techniques. In this piece, we analyze the methods used to calculate the societal costs of such populations. The people of impacted regions are concerned about increasing economic disparity, have poor trust in the future, and are experiencing a falling standard of living, according to a cross-sectional survey (n = 428) and structural equation modeling (SEM). Most people are worried about the future of their town (reported by 77.3% of respondents), the long-term effects on groundwater (reported by 77.4% of respondents), and the growing cost of living (reported by 83.4% of respondents). The study encompasses the project's life cycle, from conception and construction to decommissioning and site restoration. The findings indicate that although coal-to-gas projects may provide short-term benefits, they may not be economically sustainable in the long term. Factors such as rising natural gas prices, prospective carbon taxes, and decommissioning and site restoration costs can significantly influence the overall project expense. Hence, policymakers and energy companies must carefully evaluate the life-cycle cost of such projects before investing in them as an interim solution.

Probing individual single atom electrocatalyst sites by advanced analytical scanning transmission electron microscopy

Single atom electrocatalysts (SAEs) are promising next-generation materials for promoting a variety of important reactions, such as the oxygen reduction, nitrogen reduction, and CO2 reduction reactions. While bulk characterization techniques such as X-ray absorption spectroscopy and Mössbauer spectroscopy have significantly enhanced our understanding of these catalysts, direct probing of individual single metal atom sites at the atomic scale is necessary to understand local variations in the properties of these sites and accelerate design and synthesis of improved SAEs. Aberration-corrected scanning transmission electron microscopy (STEM) has become a powerful tool for providing this type of atomic-scale information about SAE metal sites. These sites are typically unstable under the electron beam, however, which, in combination with conventional acquisition methods and detectors, has limited the type and quantity of information obtainable by spectroscopic STEM techniques. Here, we map multiple individual SAE metal sites in a nitrogen-doped carbon containing atomically dispersed Fe and Re (FeReNC) at the atomic scale by direct electron detection electron energy-loss spectroscopy (EELS). Direct electron detection provides an improved signal-to-noise ratio over conventional scintillator-based detectors and enables detection and real space localization of weak signals. In addition, we demonstrate an automated method for identification of metal atom positions, placement of the probe on these sites, and simultaneous EELS and energy dispersive X-ray spectroscopic (EDS) signal acquisition. This simultaneous acquisition of EELS and EDS provides access to the composition and bonding of a wide range of SAE metal sites. Focusing the probe directly on the metal sites also increases the relevant data acquisition rate by more than an order of magnitude over two-dimensional mapping, enabling improved statistical measurements of site properties. The versatility, sensitivity, and speed that these techniques provide enhances our ability to probe the local elemental and chemical environment of a large number of individual SAE metal site structures at the atomic scale, enabling an improved understanding of the variations in the local properties of these electrocatalysts to be gained. As a result, significantly increased information about individual metal sites will be available to future electrochemical studies through these techniques, accelerating the development of advanced SAEs.

Development of mechanistic models for the description of radionuclide retention onto calcareous gravels

The retention capacity of natural calcareous gravels used as a filling material between the packages containing radioactive waste materials in the disposal cells was evaluated for Sr, U, Ni, Ag, 14C, 99Tc, 239Pu, 228Th and 152Eu. The thermodynamic calculations performed considering repository conditions indicated that the chemistry of most of these elements was dominated by neutral or cationic species, this is the case of 238Pu 152Eu, 228Th, Ni and Ag. The studied gravels presented high sorption capacities for these cationic or neutral species, but they are not efficient on retaining anionic species as in the case of 99Tc or Sr, which is already present in the composition of the studied gravels. For those elements where the predominant species are carbonated (14C and U) low distribution coefficients were obtained. A preliminary mechanistic sorption model was developed for each radionuclide considering carbonate (>CO3H) and calcium hydroxide (>CaOH) sites. Our preliminary model allowed to successfully reproduce the experimental trend of the data obtained in this work.

Amorphous cobalt-iron boride nanoparticles grown on B, N-doped carbon frame for efficient electrocatalytic oxygen evolution

Commencing from low-cost transition metal-based electrocatalysts, improving the catalytic activity and resource utilization is one of the ways to reduce the overall cost of hydrogen production from water cracking and improve energy conversion efficiency. Herein, the bimetallic cobalt-iron boride nanoparticles grown on the B, N-doped carbon frame (noted as CoFeB@BNC) was successfully synthesized by one-step pyrolysis boronizing using CoFe-zeolite imidazole frame (CoFe-ZIF) as the precursor and H3BO3 as the boron source. The excellent OER activity of CoFeB@BNC composite is attributed to the synergy of metal boride sites and additional B, N-doped carbon sites. Its overpotential is 297 mV at 10 mA cm−2 and 332 mV at 50 mA cm−2. Meanwhile, Tafel slope is only 43 mV dec−1, showing faster OER kinetics. The introduction of appropriate amount of Fe creates high conductivity of CoFeB@BNC composite and significantly accelerates OER kinetics. The CoFe-ZIF precursor has a large number of structure defects, which provide abundant mesoporous and active sites for the CoFeB@BNC composite. The B, N-doped carbon frame improves the conductivity and stability of the material. This work provides a feasible strategy for the design and preparation of Fe-doped ZIF-67 precursor and its derived highly active and stable boride catalyst.

On-the-Go Vis-NIR Spectroscopy for Field-Scale Spatial-Temporal Monitoring of Soil Organic Carbon

Agricultural soils serve as crucial storage sites for soil organic carbon (SOC). Their appropriate management is pivotal for mitigating climate change. Continuous monitoring is imperative to evaluate spatial and temporal changes in SOC within agricultural fields. In-field datasets of Vis-NIR soil spectra were collected on a long-term experimental site using an on-the-go spectrophotometer. Data processing for continuous SOC prediction involves a two-step modeling approach. In Step 1, a partial least square (PLSR) regression model is trained to establish a relationship between the SOC content and spectral information, including spectral preprocessing. In Step 2, the predicted SOC content obtained from the PLSR models is interpolated using ordinary kriging. Among the tested spectral preprocessing techniques and semivariogram models, Savitzky–Golay and the Gap-Segment derivative preprocessing along with a Gaussian semivariogram model, yielded the best performance resulting in a root mean square error of 1.24 and 1.26 g kg−1. A striping effect due to the transect-based data collection was addressed by testing the effectiveness of extending the spatial separation distance, employing data aggregation, and defining the distribution based on treatment plots using block kriging. Overall, the results highlight the high potential of on-the-go spectral Vis-NIR data for field-scale spatial-temporal monitoring of SOC.

Carbon doped and PTCDA co-construct S-scheme heterojunction to tune boron nitride for boosted photosynthesis hydrogen peroxide

The development of novel metal-free catalysts to photosynthesize hydrogen peroxide (H2O2) is recognized as a prospective technology for sustainable energy conversion. Herein, the carbon-doped boron nitride (BCN) and perylene tetracarboxylic dianhydride (PTCDA) formed PDA@BCN S-scheme heterojunctions with π-π stacking, which catalyzed the production of H2O2 at an unexpectedly high yield of 285.47 μmol h−1 g−1 in air. The high photocatalytic performance is attributed to the enhanced light absorption resulting in abundant carrier excitation, rapid charge separation driven by S-scheme heterojunctions, and highly selective H2O2 formation pathway. Theoretical calculations demonstrate that carbon sites in PDA@BCN can serve as an advanced active center for oxygen enrichment and activation, promoting oxygen reduction and efficient photocatalytic production of H2O2. This work lays the foundation for the design of efficient, stable, and reusable photocatalysts for environmental restoration and energy conversion.

Ligand-Metal Cooperation Enables Net Ring-Opening C-C Activation / Difunctionalization of Cyclopropyl Ketones.

Reactions that cleave C-C bonds and enable functionalization at both carbon sites are powerful strategic tools in synthetic chemistry. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of 3-carbon fragments, but general approaches to net C-C activation / difunctionalization are unknown. Herein we demonstrate the cross-coupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3-difunctionalized, ring-opened products. A combination of experimental and theoretical studies rule out more established mechanisms and shed light on how cooperation between the redox-active terpyridine (tpy) ligand and the nickel atom enables the C-C bond activation step. The reduced (tpy•-)NiI species activates the C-C bond via a concerted asynchronous ring-opening transition state. The resulting alkylnickel(II) intermediate can then be engaged by aryl-, alkenyl-, and alkylzinc reagents to furnish cross-coupled products. This allows quick access to products that are difficult to make by conjugate addition methods, such as β-allylated and β -benzylated enol ethers. The utility of this approach is demonstrated in the synthesis of a key (±)-taiwaniaquinol B intermediate and the total synthesis of prostaglandin D1.

Construction of Catalytic Fe2N5P Sites in Covalent Organic Framework-Derived Carbon for Catalyzing the Oxygen Reduction Reaction

Construction of Catalytic Fe₂N₅P Sites in Covalent Organic Framework-Derived Carbon for Catalyzing the Oxygen Reduction Reaction

An identification of arsenic retention mechanisms in column filtration systems packed with limestone

The high concentrations of arsenic in the groundwater of Zimapán, Hidalgo, Mexico, have led to the search for options that contribute to resolving this problem. In this study, we use percolation columns to remove arsenic in aqueous solutions in coexistence with ions such as fluorides, chlorides, sulfates, or bicarbonates. This filtration technique is effective and low cost since the filter material is a native limestone belonging to the Soyatal Formation of the Upper Cretaceous. This article characterizes the mechanisms of arsenic removal by calcite, the limestone's main constituent, through X-ray absorption spectroscopy (XAS). The main processes of arsenic retention in calcite are adsorption (forming corner-sharing inner-sphere surface complexes) and coprecipitation (replacing AsO4 in the carbonate site).

Ga···C Triel Bonds-Why They Are Not Strong Enough to Change Trigonal Configuration into Tetrahedral One: DFT Calculations on Dimers That Occur in Crystal Structures.

Structures characterized by the trigonal coordination of the gallium center that interacts with electron rich carbon sites are described. These interactions may be classified as Ga···C triel bonds. Their properties are analyzed in this study since these interactions may be important in numerous chemical processes including catalytical activities; additionally, geometrical parameters of corresponding species are described. The Ga···C triel bonds discussed here, categorized also as the π-hole bonds, do not change the trigonal configuration of the gallium center into the tetrahedral one despite total interactions in dimers being strong; however, the main contribution to the stabilization of corresponding structures comes from the electrostatic forces. The systems analyzed theoretically here come from crystal structures since the Cambridge Structural Database, CSD, search was performed to find structures where the gallium center linked to CC bonds of Lewis base units occurs. The majority structures found in CSD are characterized by parallel, stacking-like arrangements of species containing the Ga-centers. The theoretical results show that interactions within dimers are not classified as the three-centers links as in a case of typical hydrogen bonds and numerous other interactions. The total interactions in dimers analyzed here consist of several local intermolecular atom-atom interactions; these are mainly the Ga···C links. The DFT results are supported in this study by calculations with the use of the quantum theory of atoms in molecules, QTAIM, the natural bond orbital, NBO, and the energy decomposition analysis, EDA, approaches.

Theoretical verification on adsorptive removal of caffeine by carbon and nitrogen-based surfaces: Role of charge transfer, π electron occupancy, and temperature

Eliminating an emerging water pollutant, caffeine molecules, from an aqueous solution using carbon and nitrogen-based adsorbents is of significant interest to public health. These adsorbents have been shown to have decent adsorption capacity toward caffeine due to their surface functionality. Therefore, screening various carbon and nitrogen-based surfaces can be a better option for high-performance adsorbents to remove caffeine efficiently from wastewater. Herein, we present combined first principles and molecular dynamics quantification of the adsorption enthalpies of caffeine molecules on the possible active sites of carbon and nitrogen-based adsorbents (graphene, phagraphene, graphdiyne, single-wall carbon nanotube, fullerene, and graphitic carbon nitride) with the incorporation of Van der Waals interactions. From the DFT calculations, N-doped carbon surfaces show the highest adsorption energies of single and dimer CAF compared to pristine carbon-based adsorbents. A charge density difference and Bader charge analysis display that high charge transfer occurs between the caffeine's oxygen and the surface's nitrogen atoms. An abundance of π-electrons from the nitrogen atoms, composed of large electron clouds of aromatic rings on the graphitic carbon surface, tends to favor extensive π-π interactions with the caffeine molecule. The high value of pz electron occupancy (1.445) of N in the hexagonal ring of the graphitic surface transfers additional charge transfer, which leads to strong adsorption energy of CAF than pristine surfaces. Also, the g-C3N4 surface adsorbs the CAF molecule with higher adsorption than other N-doped carbon surfaces due to the high pz_eo (1.5448) of N atoms on the surface. At 310 K, the water molecules' kinetics aids the single and dimer caffeine molecules to adsorb with the highest adsorption energies on the active sites of g-C3N4 surfaces than graphene adsorbent.

Transformation kinetics of exogenous lead in an acidic soil during anoxic-oxic alteration: Important roles of phosphorus and organic matter

Lead (Pb) can enter soil environment during flooding events such as surface runoff and intensive rainfall. However, the key transformation processes of exogenous Pb during anoxic-oxic alteration remain poorly understood particularly how phosphorus and organic matter contribute to Pb immobilization/release. Here, a kinetic model was established to investigate the Pb transformation in an acidic soil with two levels of Pb contamination under alternating anoxic-oxic conditions, based on the results of seven-step sequential extraction, dissolved organic carbon, sulfate, iron, phosphorus, and surface sites. Results showed that the potentially available Pb, including dissolved, exchangeable, and specifically adsorbed fractions, was gradually transferred to the fulvic complex, Fe–Mn oxides bound, and sulfides bound Pb after 40-day incubation under anoxic conditions, while the fulvic complex Pb further increased after 20-day incubation under oxic conditions. The concentration of phosphorus that was extracted by 0.5 M HCl or 0.03 M NH4F in 0.025 M HCl increased under anoxic conditions and decreased under oxic conditions. When Pb-binding to phosphorus is considered during kinetic modeling, the simulated results of Pb transformation suggest that phosphorus is more important than organic matter for Pb immobilization under anoxic conditions, while the phosphates, Fe–Mn oxides, and sulfides immobilized Pb is slowly released and then complexed by fulvic acids during the re-immobilization of dissolved organic matter in soil under oxic conditions. The model established with low Pb level has been successfully applied to describe the Pb transformation with high Pb level. This study provides a comprehensive understanding of the roles of phosphorus and organic matter in controlling Pb transformation in soil from kinetic modeling.

Resonant Inner-Shell Photofragmentation of Adamantane (C10H16).

Adamantane, the smallest diamondoid molecule with a symmetrical cage, contains two distinct carbon sites, CH and CH2. The ionization/excitation of the molecule leads to the cage opening and strong structural reorganization. While theoretical predictions suggest that the carbon site CH primarily causes the cage opening, the role of the other CH2 site remains unclear. In this study, we used advanced experimental Auger electron-ion coincidence techniques and theoretical calculations to investigate the fragmentation dynamics of adamantane after resonant inner-shell photoexcitation. Our results demonstrate that some fragmentation channels exhibit site-sensitivity of the initial core-hole location, indicating that different carbon site excitations could lead to unique cage opening mechanisms.

Quasi-Three-Dimensional Cyclotriphosphazene-Based Covalent Organic Framework Nanosheet for Efficient Oxygen Reduction

HighlightsJUC-610-nanosheet exhibits highly efficient oxygen reduction reaction (ORR) catalytic activity in alkaline electrolyte with half-wave potential of 0.72 V versus reversible hydrogen electrode, which is one of the best covalent organic frameworks (COF)-based ORR electrocatalysts reported so far.It has been confirmed by experiments and density functional theory calculations that the abundant electrophilic structure in Q3CTP-COFs induces a highly density of carbon active sites, and the unique bilayer stacking facilitates the exposure of active carbon sites and accelerates the mass diffusion during ORR.JUC-610-nanosheet can also serve as a promising cathode for Zn-air batteries (power density of 156 mW cm–2 at 300 mA cm–2), which promotes the development of metal-free carbon-based electrocatalysts.

A mechanistic study of VO2 reduction on graphene-based electrodes: insights from computational quantum chemistry.

The identity of active sites for redox reactions within vanadium redox flow batteries (VRFB) are still controversial despite decades of research into the matter. Here, we use density functional theory to examine the promise of select surface functional groups as active sites and provide mechanistic insights into the reaction pathway for the positive electrode reaction. The adsorption of electroactive species to phenol and carbene-like edge carbon sites were compared using model aromatic clusters. Though phenol groups were not favorable sites for the chemisorption of VO2+ in either a V-down or O-down approach, carbene-like edge carbon sites readily adsorbed VO2+ via an oxygen-down approach, mimicking gas phase CO2 adsorption mechanisms. Subsequent steps to complete the reaction pathway were a series of proton adsorptions and reaction products desorption. The rate determining step for a reaction pathway using an edge site was the VO2+ desorption step with a Gibbs energy of activation of +84 kcal/mol.

Super-three-dimensional lithiophilic Cu-based current collector for anode-free lithium metal battery

The formation of Li dendrites and dead Li, which causes short circuits, continuous side reactions, low Coulombic efficiency (CE) and thermal runaway, severely hinders the development of anode-free lithium metal batteries. Here, Cu-based current collector with super-three-dimensional lithiophilic modification layer is developed by the pyrolysis of resorcinol formaldehyde on 3D engineered copper mesh (a-RF@3D CM). The modification layer, consisting of highly dispersed CuOx sites in the O-containing defective carbon, together with the super-three-dimensional microstructure exhibits excellent lithiophilicity and capability to effectively reduce the nucleation overpotential, accommodate the uniform dendrite-free lithium deposition, promote stable and inorganic-rich solid electrolyte interphase formation, and improve the cycle stability. As a result, the a-RF@3D CM current collector exhibits reduced nucleation overpotential of 14.2 mV and prolonged cycling life over 400 cycles with average CE >98.5%. In the LiFePO4||a-RF@3D CM anode-free cell, average CE of 99.50% and capacity retention of 60.66% are successfully achieved after 100 cycles. Meanwhile, average CE 99.78% and capacity retention of 64.43% are successfully achieved in LiFePO4||Li@a-RF@3D CM cell (N/P = 1.6) after 200 cycles. The work provides feasible way to realize the fabrication of anode-free lithium metal batteries and also enhance the understanding of solid electrolyte interface evolution and regulation strategy of Li plating–stripping in advanced Li metal-based batteries.

Remote Electronic Tuning of Chiral N-Heterocyclic Carbenes.

Our recent efforts to develop novel N-Heterocyclic carbene (NHC)-catalyzed asymmetric reactions are described. During our investigation for development of the acylation reactions via acylazoliums generated by the reactions of NHCs and α-oxidized aldehydes, we have observed significant effects of substitution at a remote site of the carbene carbon of NHCs. In addition, we also observed a significant enhancement of the enantioselectivity by the addition of carboxylate anions. From this observation, we proposed a novel working hypothesis involving a formation of a complex of the substrate and additive to reinforce the recognition of the catalyst for enhancement of the catalytic performance of the asymmetric N-heterocyclic carbene system. By applying this concept, we achieved the kinetic resolutions of both cyclic and acyclic alcohols in excellent enantioselectivities. The effects of the remote substitution were also observed in intramolecular Stetter reaction and intermolecular benzoin reaction. In these reactions, the comparison of the catalytic performance of the NHCs bearing variable remote substitutions provided insights into the reaction mechanism because the remote substitution tuned the electronic nature of NHCs without affecting the steric and electrostatic factors around the reaction site. We also developed an intramolecular benzoin condensation involving two aldehydes, which is challenging to realize. Using the substrates bearing proper protecting groups, we succeeded in the stereo divergent synthesis of a variety of inososes, which are important intermediates for the synthesis of biologically active cyclitols.