Explore the vast range of titles available.

Although the closed pore structure plays a key role in contributing low-voltage plateau capacity of hard carbon anode for sodium-ion batteries, the formation mechanism of closed pores is still under debate. Here, we employ waste wood-derived hard carbon as a template to systematically establish the formation mechanisms of closed pores and their effect on sodium storage performance. We find that the high crystallinity cellulose in nature wood decomposes to long-range carbon layers as the wall of closed pore, and the amorphous component can hinder the graphitization of carbon layer and induce the crispation of long-range carbon layers. The optimized sample demonstrates a high reversible capacity of 430 mAh g −1 at 20 mA g −1 (plateau capacity of 293 mAh g −1 for the second cycle), as well as good rate and stable cycling performances (85.4% after 400 cycles at 500 mA g −1 ). Deep insights into the closed pore formation will greatly forward the rational design of hard carbon anode with high capacity. It is essential to investigate the formation mechanism of closed pore, which contributes to low-voltage plateau capacity of hard carbon anode in sodium ion batteries. Herein, the authors explore the impact of wood precursor components and carbonization temperature on closed pore formation in hard carbon for enhanced battery performance.

During the graphitization transformation of materials in a graphitizing furnace under high temperature, a series of complex physical and chemical changes occur, and their key properties, such as thermal conductivity, electrical conductivity, and specific heat capacity, are difficult to measure directly. This paper proposes a scheme based on parameter inversion: by selecting temperature change data at key positions in the furnace, combining with the heat and electricity transfer theoretical model of the graphitizing furnace, an objective function is constructed, and the key property parameters of the materials are inferred through inversion algorithms. This method is expected to break through the technical bottleneck of direct measurement and provide an important basis for optimizing the graphitization process and improving product quality.

The highly electrically conductive graphene papers prepared from graphene oxide have shown promising perspectives in flexible electronics, electromagnetic interference (EMI) shielding, and electrodes. To achieve high electrical conductivity, the graphene oxide precursor usually needs to be graphitized at extremely high temperature (∼ 2,800 °C), which severely increases the energy consumption and production costs. Here, we report an efficient catalytic graphitization approach to fabricate highly conductive graphene papers at lower annealing temperature. The graphene papers with boron catalyst annealed at 2,000 °C show a high conductivity of ∼ 3,400 S·cm −1 , about 47% higher than pure graphene papers. Boron catalyst facilitates the recovery of structural defects and improves the degree of graphitization by 80%. We further study the catalytic effect of boron on the graphitization behavior of graphene oxide. The results show that the activation energy of the catalytic graphitization process is as low as 80.1 kJ·mol −1 in the temperature ranges studied. This effective strategy of catalytic graphitization should also be helpful in the fabrication of other kinds of highly conductive graphene macroscopic materials.

This paper presents the rapid pyrolysis results of poplar particles on a self-built semiconductor laser heating experimental platform. The effects of final temperature (400 °C, 500 °C, 600 °C) and heating rate (0.167℃/s, 10 ℃/s, 50 ℃/s and 100 ℃/s) on the biochar yield, surface morphology and graphitization degree were investigated. The results showed that final temperature and heating rate were negatively correlated with biochar yield. There are the most developed pore structures when the pyrolysis temperature is 600 °C. The influence of heating rate on biochar yield and pore structure is less pronounced than that of pyrolysis temperature on biochar yield and pore structure. The graphitization degree exhibits a trend of initially increasing and subsequently decreasing as increasing pyrolysis temperature. The highest graphitization degree is greatest at 500 °C.

In order to achieve the high-value utilization of heavy tar for the production of enhanced-performance graphite foam carbon, the carbon mesophase was ready from the heavy component of low-temperature coal tar, and the coal tar was modified by styrene-butadiene-styrene (SBS), polyethylene (PE) and ethylene-vinyl-acetate (EVA) copolymers. The order degree of the carbonite mesophase was analyzed using a polarizing microscope test, Fourier transform infrared spectroscopy and X-ray diffraction to screen out the most suitable copolymer type and addition amount. Furthermore, the mechanism of modification by this copolymer was analyzed. The results showed that adding SBS, PE and EVA to coal tar would affect the order of carbonaceous mesophase; however, at an addition rate of 10.0 wt.%, the linear-structure SBS copolymer with a styrene/butadiene ratio (S/B) of 30/70 exhibited the optimal degree of ordering in the carbonaceous mesophase. Its foam carbon prepared by polymer modification is the only one that forms a graphitized structure, with d002 of 0.3430 nm, and the maximum values of Lc and La are 3.54 nm and 2.22 nm, respectively. This is because, under elevated pressure and high-temperature conditions, SBS underwent chain scission, releasing a more significant number of methyl and other free radicals that interacted with the coal tar constituents. As a result, it reduced the affinity density of heavy coal tar molecules, enhanced fluidity, promoted the stacking of condensed aromatic hydrocarbons and increased the content of soluble carbonaceous mesophase, ultimately leading to a more favorable alignment of the carbonaceous mesophase.

Porous carbon skeletons (PCSs) derived from isocyanate-based aromatic polyimide foams (PIFs) by high-temperature pyrolysis are very promising in the fabrication of high-performance polymer composite foams for electromagnetic interference (EMI) shielding due to their efficient conductive networks and facile preparation process. However, severe volumetric shrinkage and low graphitization degree is not conducive to enhancing the shielding efficiency of the PCSs. Herein, ferric acetylacetonate and carbon-nanotube coating have been introduced in isocyanate-based PIFs to greatly suppress the serious shrinkage during pyrolysis and improve the graphitization degree of the final carbon foams through the Fe-catalytic graphitization process, thereby endowing them with better EMI-shielding performance even at lower pyrolysis temperature compared to the control samples. Moreover, compressible polydimethylsiloxane (PDMS) composite foams with the as-prepared carbon foams as prefabricated PCSs have also been fabricated, which could provide not only stable shielding effectiveness (SE) performance even after a thousand compressions, but also multiple functions of Joule heating, thermal insulation and infrared stealth. This study offers a feasible route to prepare high-performance PCSs in a more energy-efficient manner via PIF pyrolysis, which is very promising in the manufacture of multifunctional conductive polymer composite foams.

This paper investigates the impact of pressure on the surface performance and layer structure of amorphous carbon-based films containing chromium through argon annealing and pressure argon annealing. The results indicate that significant changes to the layer structure of amorphous carbon-based films are observed after pressure annealing. After 500°C pressure annealing, although the total thickness of amorphous carbon-based films does not change, the boundary between the sublayers in the film moves down 400 nm. Pressure promotes the diffusion of elements within the sublayers, triggering boundary movement in amorphous carbon-based films during pressure annealing. At the same annealing temperature, the film surface is smoother after annealing in argon compared to annealing in pressure argon. The lower roughness after argon annealing corresponds to a lower content of sp 3 bonds. The surface hardness of the film after annealing in pressure argon is higher than that after annealing in argon, suggesting that pressure slows down the reduction in film hardness by delaying the graphitization process of the film.

Graphene, a single-layer network of carbon atoms, has outstanding electrical and mechanical properties 1 . Graphene ribbons with nanometre-scale widths 2 , 3 (nanoribbons) should exhibit half-metallicity 4 and quantum confinement. Magnetic edges in graphene nanoribbons 5 , 6 have been studied extensively from a theoretical standpoint because their coherent manipulation would be a milestone for spintronic 7 and quantum computing devices 8 . However, experimental investigations have been hampered because nanoribbon edges cannot be produced with atomic precision and the graphene terminations that have been proposed are chemically unstable 9 . Here we address both of these problems, by using molecular graphene nanoribbons functionalized with stable spin-bearing radical groups. We observe the predicted delocalized magnetic edge states and test theoretical models of the spin dynamics and spin–environment interactions. Comparison with a non-graphitized reference material enables us to clearly identify the characteristic behaviour of the radical-functionalized graphene nanoribbons. We quantify the parameters of spin–orbit coupling, define the interaction patterns and determine the spin decoherence channels. Even without any optimization, the spin coherence time is in the range of microseconds at room temperature, and we perform quantum inversion operations between edge and radical spins. Our approach provides a way of testing the theory of magnetism in graphene nanoribbons experimentally. The coherence times that we observe open up encouraging prospects for the use of magnetic nanoribbons in quantum spintronic devices. By functionalizing molecular graphene nanoribbons with stable spin-bearing nitronyl nitroxide radical groups, delocalized magnetic edge states are observed, with microsecond-scale spin coherence times.

Oxygen-containing carbons are promising supports and metal-free catalysts for many reactions. However, distinguishing the role of various oxygen functional groups and quantifying and tuning each functionality is still difficult. Here we investigate the role of Brønsted acidic oxygen-containing functional groups by synthesizing a diverse library of materials. By combining acid-catalyzed elimination probe chemistry, comprehensive surface characterizations, 15 N isotopically labeled acetonitrile adsorption coupled with magic-angle spinning nuclear magnetic resonance, machine learning, and density-functional theory calculations, we demonstrate that phenolic is the main acid site in gas-phase chemistries and unexpectedly carboxylic groups are much less acidic than phenolic groups in the graphitized mesoporous carbon due to electron density delocalization induced by the aromatic rings of graphitic carbon. The methodology can identify acidic sites in oxygenated carbon materials in solid acid catalyst-driven chemistry. Distinguishing the influence of oxygen functional groups in carbon materials is important but elusive. Here, the authors combine experimental and machine learning techniques and reveal that phenolic groups are more acidic than carboxylic groups.

Fe–N–C catalysts are the most promising platinum group metal-free oxygen-reduction catalysts, but they suffer from a low density of active metal sites and the so-called activity–stability trade-off. Here we report an Fe–N–C catalyst prepared by adding an optimal amount of H 2 to the traditional inert atmosphere during the thermal activation. The presence of H 2 significantly increases the total density of FeN 4 sites, suppressing the unstable pyrrolic-N-coordinated S1 sites and favouring the stable pyridinic-N-coordinated S2 sites with shortened Fe–N bond lengths. We propose that the intrinsically stable S2 sites are probably arranged in well-graphitized carbon layers, and the S1 sites exist in less-graphitized carbon. H 2 could remove unstable S1 sites and retain stable S2 sites during the pyrolysis to break the challenging activity–stability trade-off. The Fe–N–C catalyst in membrane electrode assemblies maintains a current density of 67 mA cm −2 at 0.8 V (H 2 –air) after 30,000 voltage cycles (0.60 to 0.95 V under H 2 –air), achieving encouraging durability and performance simultaneously. Fe–N–C catalysts are a promising alternative to precious metals in fuel cell cathodes, but they suffer from durability issues. Now, a preparation method is reported that allows increasing the active site density while also improving durability.