Carbon Crystallites Research Articles

Broken crystal symmetry of MWCNTs as the key factor in improvement of carboxyl functionalization

Carbon nanotubes functionalized with carboxyl groups (COOH-CNTs) find their application in energy storage, sensing, improving mechanical stability and biomedicine. So a facilitation of COOH-groups bonding to CNTs is one the modern scientific challenges. In this study untreated multi-walled CNT (MWCNTs), nitrogen-doped MWCNT (N-MWCNTs) and ion-beam irradiated N-MWCNTs (irr-N-MWCNTs) were synthesized using the CVD method. Characterizations were performed via HRTEM, Raman, XPS, and NEXAFS spectroscopy. Irr-N-MWCNTs demonstrated the largest amount of carbon crystallites, the presence of Stone-Wales defects as well as the regions of tensile-compressive, shear and torsional deformation. All these factors contributed to increase of carboxyl functionalization at the tube’s surface. On the base of experimental data, the atomic supercells of N-MWCNTs and irr-N-MWCNTs were built by the self-consistent-charge density-functional tight-binding method (SCC DFTB). Through SCC DFTB, we quantified atomic rearrangements, electronic structures, charge transfers, total energies, and the forces and energy barriers relevant to COOH bonding. The twisting of irr-N-MWCNTs supercells by 45 degrees decreased the barrier to the carboxyl formation in 2.5 times in comparison to undeformed nanotubes. Our findings reveal that nitrogen addition, ion-beam irradiation, and induced deformations create the necessary conditions for COOH functionalization by altering the physicochemical surface properties of MWCNTs.

Synthesis of biowaste-derived nanostructured material for the nanomolar detection of glucose: Biological sample analysis

Glucose electro-oxidation in an alkaline media was investigated using an electrode composed of carbon paste and sugarcane bagasse activated carbon (SBAC). The SBAC was prepared using an easy, affordable, and environmental friendly process. The porous activated carbon was produced using sugarcane bagasse through a pre-treatment process that involved carbonization at 650 °C and K2CO3. X-ray diffraction (XRD) was used to observe the formation of carbon crystallites during activation at higher temperatures. The Fourier-transform infrared (FTIR) spectrum shows functional groups that are present in the carbon material. The carbon sample's morphology was evaluated using scanning electron microscope (SEM). The surface roughness was studied using atomic force microscopy (AFM). Porous activated carbon derived from sugarcane bagasse was carefully mixed into electrode components such as graphite powder and mineral oil for glucose (GLS) detection. For precise GLS detection, the SBACs were employed as non-enzymatic electrochemical sensor probes in their as-prepared condition. According to the electrochemical experiments, the constructed sensor shows exceptional electrochemical performance towards glucose oxidation, including excellent selectivity, a low detection limit, good sensitivity, and a wide linear range. Investigation has been conducted on the oxidation of GLS in alkaline solutions with varying concentrations of halide ions such as iodide and chloride. The GLS oxidation peak current increased the performance of a SBAC modified electrode was compared to that of a bare carbon paste electrode (CPE). The role of sensitivity in minimizing halide poisoning is significant. The risk of poisoning is increased if iodide > chloride. As the modified electrode's voltage changes in a chloride solution containing glucose, the peak current gradually reduces. The redesigned electrode that is currently in use as a consequence not only promotes glucose oxidation but also shows strong resistance to electrode poisoning caused by halides. The sensitive and targeted SBAC/CPE has also improved its reliability while evaluating samples of human serum, urine, and breast milk.

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Experimental study on evolution and mechanism for dielectric response of different rank coals in terahertz band

Terahertz technology holds the potential for applications in identifying risks and development stages of coal spontaneous combustion (CSC). However, one critical factor influencing the precision of THz technology in CSC applications is the coal rank. In light of these, this study aimed to investigate the permittivity (0.4–1.6 THz) of different rank coals. Additionally, its underlying mechanism was analyzed utilizing Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Results indicate that increased coal rank leads to a decrease in both real permittivity (from 2.462 to 2.327) and imaginary permittivity (from 0.0447 to 0.0250), primarily due to diminished moisture (from 12.82 % to 1.35 %). After moisture removal, increased coal rank results in an increased real permittivity (from 2.292 to 2.315), primarily due to the carbon crystallite (interlayer spacing changed from 3.553 to 3.529, and stacking height shifted from 14.805 to 19.743) and microstructure profiles. Moreover, minerals are identified as another primary factor affecting real permittivity. For imaginary permittivity, increased coal rank leads to a decrease (from 0.0411 to 0.0245), primarily due to oxygen-containing functional groups (from 42.96 % to 31.71 %). The conclusion advances the fundamental theoretical research on coal permittivity, providing a solid theoretical foundation for THz technology in CSC applications.

Catalytic Gasification of Petroleum Coke with Different Ratios of K2CO3 and Evolution of the Residual Coke Structure.

The catalytic gasification of petroleum coke with different ratios of K2CO3 was investigated by a thermogravimetric analyzer (TGA) using the non-isothermal method. The initial, peak, and final gasification temperatures of the petroleum coke decreased greatly as the amount of K2CO3 increased, and the catalytic reaction became saturated at a concentration of K+ higher than 5 mmol/g; with the further increase in catalyst; the gasification rate varied slightly, but no inhibition effect was observed. The vaporization of the catalyst was confirmed during the gasification at high temperatures. The structural evolution of the residual coke with different carbon conversions was examined by X-ray diffraction (XRD), Raman spectroscopy, and N2 adsorption analyses during gasification with and without the catalyst. The results showed that the carbon crystallite structure of the residual coke varied in the presence of the catalyst. As the carbon conversion increased, the structure of the residual coke without the catalyst became more ordered, and the number of aromatic rings decreased, while the graphitization degree of the residual coke in the presence of the catalyst decreased. Meanwhile, the surface area and pore volume of petroleum coke increased in the gasification process of the residual coke, irrespective of the presence of the catalyst. However, the reactivity of the residual coke did not change much with the variation in the carbon and pore structure during the reaction.

Experimental investigation of metallic partial-flow particulate filter on a diesel engine's combustion pressure and particle emission

The study aims to present the combustion and exhaust behaviors of a 3 L, four-cylinder common rail diesel engine with three different kinds of conventional B7 diesel fuels with and without a platinum diesel oxidation catalyst (DOC) system and non-catalytic partial flow through a diesel particulate filter (P-DPF). Testing is performed under the three different operating conditions, idle to medium engine loading at 1000, 1500, and 2000 engine revolutions per minute with four different engine torques of 84, 112, 140 and 160 Nm. The surface morphology and agglomerate size of particulate matter (PM), single primary particle analysis as well as the fringe length of the carbon crystallite structure were also examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS) to achieve a better understanding through image processing. The P-DPF system does not have a significant effect on an engine's in-cylinder combustion characteristics and brake thermal efficiency. The diesel engine's particle emissions are reduced by trapping them on the metallic micro-fibers of a P-DPF. CO2, NO, and O2 levels show that the carbonaceous particle emissions on the micro-structure of the P-DPF passively react with NO2 and O2. Consequently, diesel engine particle emissions can be reduced by around 50% using a P-DPF system under the experimental conditions of the current study.

The mitigation of pitch-derived carbon with different structures on the volume expansion of silicon in Si/C composite anode

The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes. However, the interaction between Si and carbon materials with different structures is still unclear. Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures. Herein, different types of mesophase pitch (domain, flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials. The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface. The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability. While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay. These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.

Iron Nanoparticles to Catalyze Graphitization of Cellulose for Energy Storage Applications

The production of highly graphitic carbon from bioresources is an environmentally friendly approach to synthesize graphene for energy storage applications. Iron catalytic graphitization of cellulose, the most abundant biopolymer on earth, is an alternative approach as until now, cellulose has been classified as poorly graphitizable material. In this study, the impact of processing temperature and iron impregnation on the extent of graphitization of the cellulose-derived graphitic carbon nanostructure is uncovered by combining Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and X-ray pair distribution function analysis. Raman spectroscopy is used in an innovative way to describe the evolution of the average graphitic phase size where the ash content misguides the X-ray diffraction analysis. A correlation was established between (i) the in-plane crystallite size La and the ID″/IG first-order ratio, (ii) the out-of-plane Lc crystallite size and the IG/Itot′ second-order ratio, and (iii) the second-order Raman IG′/Itot′ ratio and the average number of carbon layers per carbon crystallite. For iron-impregnated cellulose, phase quantification and analysis of the spatial distribution reveal highly crystalline rhombohedral graphite surrounded by a nanocrystalline carbon matrix. We explicitly show that traditionally non-graphitizable carbons can be used to form a graphite-like structure with multilayers of graphene sheets by careful addition of widely available nontoxic metal as catalysts. The study also shows that the impact of the catalyst is much more effective than the temperature in the nanostructure transformation. The proposed approach and the results obtained provide interesting insights that should stimulate further works aimed at extending the knowledge in the field.

Unveiling the transformation of liquid crystalline domains into carbon crystallites during carbonization of mesophase pitch-derived fibers

Despite extensive studies on structural changes during the carbonization process of pitch-derived fibers, an accurate description of the transformation from liquid crystalline domains into carbon crystallites is still limited to a few depictions based on common analytical tools for carbon fibers. We employed small-angle X-ray scattering (SAXS) with model fits for the unification of such disparate measures. The carbonization process below 1200 °C is divided into three sequential regimes: Regime I - disruption of stacked polyaromatic mesogens with fluctuations in elasticity from 300 to 600 °C; Regime II - full-scale transformation with enhancement in orientation from 600 to 800 °C; and Regime III - development of semi-crystalline carbon structures with elongation of microvoids from 800 to 1200 °C. By examining the viscoelastic properties of pitch-derived fibers during heat treatment below 600 °C (Regime I), we found that the maximum softness of the pitch-derived fibers is achieved at 500 °C. This is due to the decrease in crosslink density between stacking structures, indicating that the crosslink density below 600 °C is a significant contributor to the formation of carbon crystallites.

Effect of Temperature on the Graphitizability and Electrochemical Properties of a Quang Ninh Natural Anthracite Used As Anode in Li/Na-Ion Batteries

In this research, natural anthracite coal (ATC) originated from Vang Danh - Quang Ninh province in Viet Nam was firstly chemically purified and then calcined in inert gas (Ar) at 800 oC for different periods (t = 2, 3 and 6 h) to remove all the impurities and enrich the carbon content. The purity and graphitized structure of treated coal proved significantly while evaluating its structural parameters (the lateral crystallite size - La, stacking crystallite height - Lc, the average number of layers per carbon crystallite - Naverage, and the average number of carbon atoms per aromatic lamellae - n)1, 2 and morphology. After purification step, ATC possesses relatively high carbon content (96.0%) and its impurities were mostly removed. The structure of heat-treated ATC samples is like hard carbon. Besides, its graphene interlayer spacing is larger than that of graphite. These features seem to be potential for application of ATC as negative electrode materials for both Li and Na rechargeable batteries.In batteries testing, using ATC calcined at 800 oC for 3 hours as anode material in lithium half-cell exhibited a quite good specific capacity (170.1 mAh g-1), which is much higher than the value obtained for commercial hard carbon (162.2 mAh g-1). Moreover, Coulombic efficiency of ATC is almost absolute (99.8%). In sodium half-cell, the sample calcined at 800 oC for 2 hours gave much smaller specific capacity of 130.5 mAh g-1 than hard carbon one (280 mAh g-1). Nevertheless, Coulombic efficiency of ATC anode in lithium half-cell and sodium half-cell throughout 100 cycles remained absolutely at 99.6%, while their values for hard carbon anode were 99.9% and 99.7%, respectively. References Abou-Rjeily, J.; Laziz, N. A.; Autret-Lambert, C.; Outzourhit, A.; Sougrati, M.-T.; Ghamouss, F., Towards valorizing natural coals in sodium-ion batteries: impact of coal rank on energy storage. Scientific Reports 2020, 10 (1), 1-10.Manoj, B.; Kunjomana, A., Study of stacking structure of amorphous carbon by X-ray diffraction technique. Int. J. Electrochem. Sci 2012, 7 (4), 3127-34. Acknowledgement This work is supported by Viet Nam National University Ho Chi Minh City (VNUHCM) under grant number B2020-18-06

Altering Thermal Transformation Pathway to Create Closed Pores in Coal‐Derived Hard Carbon and Boosting of Na+ Plateau Storage for High‐Performance Sodium‐Ion Battery and Sodium‐Ion Capacitor

AbstractCoal features low‐cost and high carbon yield and is considered as a promising precursor for carbon anode of sodium‐ion batteries (SIBs) and sodium‐ion capacitors (SICs). Regulation of microcrystalline state and pore configuration of coal structure during thermal transformation is key to boost Na+ storage behavior. Herein, a facile strategy is reported to create abundant closed pores in anthracite‐derived carbon that greatly improves Na+ plateau storage. An altered thermal transformation pathway of chemical activation followed by high‐temperature carbonization is adopted to achieve the conversion of open nanopores and ordered carbon crystallite into closed pores surrounded by short‐range carbon structures. The optimized sample delivers a large reversible capacity of 308 mAh g–1 that is dominantly contributed by the low‐voltage plateau process. Experimental results reveal the enhanced pore‐filling mechanism in the developed closed pores. Benefitting from the improved plateau behavior, the constructed SIB delivers a high‐energy density of 231.2 Wh kg–1 with an average voltage of 3.22 V; the assembled full‐carbon SIC shows high energy and power densities (101.8 Wh kg–1 and 2.9 kW kg–1). This work provides a universal thermal transformation approach for designing high‐performance carbon anode with closed porosity from low‐cost and highly aromatic precursors.

Unveiling the Transformation of Liquid Crystalline Domains into Carbon Crystallites During Carbonization of Mesophase Pitch-Derived Fibers

Unveiling the Transformation of Liquid Crystalline Domains into Carbon Crystallites During Carbonization of Mesophase Pitch-Derived Fibers

Unveiling the Transformation of Liquid Crystalline Domains into Carbon Crystallites During Carbonization of Mesophase Pitch-Derived Fibers

Unveiling the Transformation of Liquid Crystalline Domains into Carbon Crystallites During Carbonization of Mesophase Pitch-Derived Fibers

Biodiesel soot combustion: Analysis of the soot-catalyst contact in different experimental conditions

To simulate the oxidation of Biodiesel soot in a catalyzed Diesel Particulate Filter, oxidation experiments of undoped or Na-doped model soot were performed in the presence of Pt-Pd/Al2O3 under Temperature Programmed Oxidation and different carbon-catalyst configurations. Loose or tight contact was simulated by mixing soot and catalyst either with a spatula or in a mortar. Samples were characterized by Flame Atomic Adsorption Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy, N2-physisorption, X-ray Photoelectron Spectroscopy, Raman Spectroscopy and Transmission Electron Microscopy coupled with Energy Dispersive X-Ray. The results showed that reducing the carbon granulometry led to an enhancement of the reactivity under NO2, due to the external combustion mechanism of carbon crystallite. In the absence of catalysts, no impact of the granulometry was observed under a flue gas containing NO and O2. A better catalyst efficiency was obtained when the carbon-catalyst contact was increased. In tight contact, a mechanism where NO2 can react adsorbed on a metallic site with a carbon site was proposed. In the presence of water, a simple addition of the catalytic activity of both water and Pt-Pd/Al2O3 catalyst impact on carbon oxidation was observed. The use of Biodiesel, simulated by Na-doped model soot, led to a significant increase in the catalyst efficiency in loose contact. Thus, a second mechanism was proposed, assuming that the doped sites play the role of NO2-reservoir and carrier between catalyst and carbon sites.

Investigation on the influence of wood pellets on the reactivity of coke with CO2 and its microstructure properties

Adding 5 mass% wood pellets in a coal blend affects the reactivity with CO2 and microstructural properties of the coke at different final coking temperatures of 950 and 1100 °C. A correlation between coke reactivity index (CRI) and BET specific surface area was found. The reactivity of coke and biocoke decreases with a decrease in the specific surface area, as well as with an increase in the carbonization temperature. Raman spectroscopy results indicate that the higher carbonization temperature of biocoke mitigates the effect of 5 mass% of biomass addition. The X-ray diffraction-based interlayer spacing of carbon crystallite (d002) decreases slightly with increasing carbonization temperature, and crystallite height (Lc) increases with rising coking temperature for both coke and biocoke. Additionally, the lower the d002 value, the lower the CRI of the cokes and biocokes. A good correlation between CRI and d002 is observed. Carbon crystallite width (La) values increased with a rising carbonization temperature, indicating the intensive growth of carbon crystallites in all directions. However, these values for biocokes are lower due to the presence of charcoal particles.

Study on pyrolysis behavior of the coal fractions based on macro maceral separation

In this paper, a sub-bituminous coal was separated into several maceral-rich fractions by float-sink method and the low temperature pyrolysis behavior of the separated fractions were further evaluated. The results showed that, the raw coal could be successfully separated into vitrinite-rich, inertinite-rich and mineral-rich fractions. Compared with the raw coal, the vitrinite was enriched from 50.8% to 65.2% in the vitrinite-rich fraction, the inertinite was enriched from 37.2% to respectively 47.3% and 51.6% in the two inertinite-rich fractions, and the minerals content increased from 11.20% to 38.40% in the mineral-rich fraction. The enriched aliphatic long-chain structures and alkyl side chains on aromatic rings caused the highest tar yield (dry basis) of 16.21% in the vitrinite-rich fraction, almost 4.16% higher than that of the raw coal (12.05%). Moreover, the tar also had the highest aliphatic hydrocarbons content which is beneficial for further upgrading. The inertinite-rich fractions were enriched in regular aromatic and hydroaromatic structures, so that a higher polycyclic and naphthol content in the tar was obatained. The mineral-rich fraction had the highest stacking height for the carbon crystallites and was enriched in small aromatic clusters, resulting in a larger amount of benzenes and naphthalene in the tar. It is believed that this work provides a good guidance that the prior separation is beneficial to the further staged utilization of sub-bituminous coal.

Study on the Physical, Chemical and Combustion Characteristics of Pyrolysis Semi-coke

ABSTRACT Combustion is an effective method for large-scale utilization of pyrolytic semi-coke (SC), a high order carbon-based solid fuel with low volatile content. The combustion characteristics of SC can be deeply understood through the study of physical and chemical properties. Taking SC as the research object and anthracite (YQ) with similar chemical composition as the control, the activation energy (E) of SC and YQ was calculated respectively by using model-free method and model method (16 typical mechanism functions). The pre-exponential factor (A), the change of enthalpy (ΔH), the change of entropy (ΔS), and the change of Gibbs free energy (ΔG) during the reaction were calculated. As a result, the pore inside of the particle is the main part of the pore structure of SC. The total specific surface area, pore-volume, and fractal dimension of SC are all larger than that of YQ. There is a lot of amorphous carbon in both SC and YQ, and the lattice spacing and graphitization degree of SC is smaller than that of YQ, but the average aromatic carbon lateral size and crystallite volume are much larger than that of YQ. The carbon in SC and YQ mainly exists in the form of aromatic carbon and aliphatic carbon, and the relative content of aromatic carbon in SC and YQ is basically the same. For the model method, the E of SC and YQ calculated by the three-dimensional diffusion (Spherical symmetric) mechanism function is the closest to the E obtained by the model-free method. Different from YQ, the main combustion stage of SC is composed of fixed carbon combustion and CaCO3 decomposition, and basically, no NH3 and HCN are generated. The volatile content of SC, the total specific surface area, and the pore volume in the pore are larger than that of YQ, which results in that the ignition temperature of SC is lower than that of YQ. The E and burn-out temperature of SC are higher than that of YQ due to the lower oxygen-containing functional group content, higher aromatic carbon content, fractal dimension and larger crystallite volume. Comprehensive physical, chemical, and combustion characteristics results show that using SC by combustion is more difficult than YQ.

Crystallite structure of Palm shell Activated Carbon/MgO and Its Influence on Carbon Monoxide and Carbon Dioxide Adsorption

Gas emission of the motor vehicle is a major contributor to climate change, with a total of 14% emission annually, and the best potential option for reducing pollution is using the adsorption method. Magnesium oxide (MgO) has been proven as an effective adsorbent for liquid and gases. The impregnation of MgO on porous structure increases the affinity toward nonpolar gases, which is one of the purposes of this study. The crystallite structure is also a key factor that determines the adsorption capacity of activated carbon (AC). However, deeper analysis is needed in the activated carbon crystallite structure represented by d002 (aromatic layer), Lc (crystallite height), and La (crystallite diameter) on the adsorption of motor vehicle gas emissions. Three types of palm shell-based activated carbon were tested in this experiment. The results showed that activated carbon made using the two-step method and the AC/MgO produced surface structure with a d002 value of 0.33 nm and 0.32 nm, respectively. The impregnation of MgO on AC showed changes in surface structure and affected its crystallinity. The ability to adsorb CO2 and CO by AC/MgO increase up to 80% and 88%, respectively.

Physicochemical characterization of direct injection Engines's soot using TEM, EDS, X-ray diffraction and TGA

The physical characteristics and elemental composition of particulate matters (PMs) from gasoline direct injection spark ignition (GDI-SI) engines were successfully investigated using transmission electron microscopy - energy dispersive X-ray spectroscopy (TEM-EDS). Thermogravimetric analysis (TGA) was used to analyze the PMs oxidation. The morphology of agglomerated GDI-PMs is not significantly different from the diesel direct injection compression ignition (DDI-CI) engine's PMs. The spherical single primary nanoparticles of the engine's soot composed of curve line carbon crystallites. The average diameter size of the single primary nanoparticles of GDI, DDI, and carbon black are approximately 24 nm, 26 nm, and 31 nm, while the inter-planar spacing is about 0.364 nm, 0.358 nm, and 0.356 nm, respectively. The total fringe lengths of GDI, DDI, and carbon black are approximately 154 nm, 159 nm, and 163 nm measured from the areas of 10 nm × 10 nm inner core regions of primary nanoparticles, and are 180 nm, 195 nm, and 228 nm from the outer shell regions, respectively. The total fringe lengths of inner core are shorter than the outer shell. Besides, the engine's PMs contains both crystalline and amorphous carbon structure using XRD analysis. The GDI-PMs had the least crystalline structure compared to the DDI-PMs and carbon black due to the higher percentage of amorphous fraction. TGA analysis showed that the GDI-PMs oxidation was faster than the DDI-PMs and CB-N330 oxidation because of the primary particle size, the fringe length, and the crystal size which have an impact on oxidation kinetics of particulate matters.

Flexible temperature sensors made of aligned electrospun carbon nanofiber films with outstanding sensitivity and selectivity towards temperature.

Continuous real-time measurement of body temperature using a wearable sensor is an essential part of human health monitoring. Electrospun aligned carbon nanofiber (ACNF) films are employed to assemble flexible temperature sensors. The temperature sensor prepared at a low carbonization temperature of 650 °C yields an outstanding sensitivity of 1.52% °C-1, high accuracy, good linearity, fast response time and excellent long-term durability. Moreover, it exhibits high discriminability towards temperature amidst other unwanted stimuli and maintains its original performance even after repeated stretch/release cycles because of highly-aligned structures. The correlation between the atomic structure and the temperature sensing performance of ACNF sensors is established. Contrary to conventional highly conductive temperature sensors, the ACNF sensor with a low electrical conductivity prepared at a low carbonization temperature ameliorates the temperature sensing performance. This anomaly is explained by (i) the smaller and more disordered sp2 carbon crystallites yielding a high negative temperature coefficient, (ii) a larger number of defects, and (iii) a higher pyridinic-N content generating abundant entrapped and localized electrons which are activated once sufficient thermal energy is available. Flexible ACNF sensor's overall performance is among the best-known carbon material-based flexible temperature sensors, demonstrating potential applications in emerging healthcare and flexible electronics technologies.