Single-walled carbon nanotubes (CNTs) have emerged as promising metal-free catalysts for oxygen reduction reactions (ORR) in microbial fuel cells (MFCs) due to their high electrical conductivity and structural tunability. In this study, CNTs were doped with nitrogen and sulfur (N,S-CNT) through a pyrolysis route using thiourea, following oxidative acid treatment, which helps to introduce defects and anchoring sites. X-ray photoelectron spectroscopy (XPS) confirmed successful incorporation of pyridinic-N, pyrrolic-N, and thiophenic-S species, while Raman spectroscopy revealed increased structural disorder without compromising the integrity of the CNT framework. Electrochemical test in alkaline media demonstrated that N,S-CNT exhibited an improved onset potential of 0.82 V vs SHE and an electron transfer number approaching 3.6, which indicates enhanced ORR activity and selectivity compared to pristine and N-doped CNTs. Chronoamperometric stability testing further showed minimal performance degradation over six hours. When applied as a cathode material in a single-chamber MFC, N,S-CNT achieved a peak power density of 126 mW/m², more than twice that of the undoped benchmark cathode, while also exhibiting lower area-specific resistance. These results highlight the synergistic benefits of N and S co-doping in CNTs for efficient and durable ORR electrocatalysis in MFC applications.

The chemical reactivity of carbon materials is primarily governed by edge sites; however, this reactivity may also depend on the energy levels of π-electrons, specifically the Fermi level. To verify this hypothesis, experiments must be conducted using carbon materials with consistent structural and functional group compositions, while varying only the Fermi level. In this study, we prepared carbon thin films with thicknesses of several nanometers via chemical vapor deposition on Al₂O₃ nanoparticles. The structure, as well as the quantity and quality of edge sites in the carbon films, remained constant regardless of the number of carbon layers—except in the case of a single layer. In contrast, work function measurements showed that the Fermi level varied depending on the number of carbon layers. When cobalt was supported on these carbon thin films, and the reduction and carbonization behavior of cobalt were examined, the composition of cobalt species was found to change with the number of carbon layers. These results indicate that the Fermi level of carbon influences the chemical reactivity between the carbon support and cobalt, providing new insights into tuning the reactivity of carbon materials through Fermi-level control.

This study provides direct quantitative evidence that hydroxyl radicals (•OH) play a significant role in the degradation of Fe–N–C catalysts during the oxygen reduction reaction (ORR) under specific electrochemical conditions. Using a radical trapping method with coumarin, we demonstrate that at 0.6 V, •OH is generated in proportion to H₂O₂ production and correlates strongly with the catalyst degradation rate. This finding offers the first experimental confirmation of the long-suspected •OH-driven degradation pathway in non-precious metal catalysts. In contrast, at 0.8 V, degradation occurs with negligible •OH formation, indicating alternative pathways such as oxidative Fe demetalation or nitrogen species modification. Post-degradation structural analyses support this scenario, revealing voltage-dependent changes in surface oxygen content, nitrogen speciation, and Fe–N_x site abundance. These results emphasize the importance of identifying radical-mediated contributions to catalyst instability and provide insights for improving the durability of Fe–N–C electrocatalysts.

This study examines the effect of MnO₂ crystallinity on the performance of lithium–oxygen batteries (LOBs). Low- and high-crystallinity MnO₂ (LC-MnO₂ and HC-MnO₂) were synthesized and used to fabricate positive electrodes composed of activated carbon aerogels (ACA). In this configuration, the ACA provides a high-surface-area, electronically conductive support that serves as a substrate for Li₂O₂ deposition and ensures efficient electron transport to the MnO₂ catalyst. Structural analyses showed that LC-MnO₂ exhibited broader X-ray diffraction peaks and a larger surface area than HC-MnO₂, indicating lower crystallinity and a higher density of oxygen vacancies. Electrochemical measurements revealed that the LC-MnO₂/ACA electrode delivered lower charging voltages and markedly improved cycling stability, sustaining approximately 70 more cycles than the HC-MnO₂/ACA electrode at a fixed capacity of 300 mAh g⁻¹. These enhancements are attributed to the increased surface area and oxygen vacancies, which facilitate Li⁺ insertion and promote Li₂O₂ formation on the catalyst surface. Together with the high-surface-area, electronically conductive ACA support, the findings highlight the crucial role of crystallinity in both discharge and charge reactions in LOBs, demonstrating that low-crystallinity MnO₂ is a promising catalyst for improving overall battery performance.

Biochar soil amendment has gained attention as a strategy to enhance nitrogen (N) use efficiency and reduce N losses in agricultural systems. This study evaluated the effects of co-applying non-labelled ammonium sulphate and ¹⁵N-labelled ammonium sulphate with rice husk-derived biochar produced at 400 °C, 600 °C, and 700 °C on the ¹⁵N uptake in tall fescue (Festuca arundinacea) during a 90-day greenhouse experiment. The results showed that the treatment using 400 °C biochar in combination with ammonium sulphate fertilizer significantly enhanced the uptake and retention of ¹⁵N ammonium sulphate. This treatment resulted in the highest percentage of nitrogen derived from the fertilizer, the greatest cumulative recovery of ¹⁵N in plants (77.7%), and the lowest potential N losses (22.1%). In contrast, treatments with biochars produced at 600 °C and 700 °C showed intermediate performance, while the treatment with ammonium sulphate alone (without biochar) exhibited the lowest ¹⁵N recovery (47.9%) and the highest N losses (51.9%). The superior performance of the 400 °C biochar treatment is likely attributed to its higher cation exchange capacity, and, the presence of oxygenated-containing functional groups, which favor ammonium adsorption. Conversely, the biochars produced at higher temperatures showed increased aromaticity, larger specific surface areas, and higher degree of crystallinity. However, they exhibited lower cation exchange capacity, which was likely due to the loss of polar functional groups. As a result, their ability to retain nutrients was limited. Some mechanistic interpretations were inferred from comparable literature, highlighting the need for direct characterization through X-ray diffraction and N₂ adsorption analysis. Overall, this research highlights the importance of selecting biochar with an appropriate carbonization temperature to optimize nitrogen retention and improve fertilizer efficiency in pasture production systems.

Among C₆₀ compounds, A₆C₆₀ is regarded as an insulator because the t_1u derived LUMO is fully filled. Although C₆₀ compounds have been extensively studied for many years, the physical properties of A₆C₆₀ were not investigated due to experimental difficulties. In present study, we successfully detected the temperature dependence of electrical resistivity of K₆C₆₀ in bulk under dry condition. Contrary to expectation, experimentally estimated E_g was significantly smaller than those of previous reports. On the other hand, the thermal activating behavior did not obey Arrhenius law and VRH models in whole temperature range. This anomalous behavior may be attributed to lattice dynamics. The resistivity data based on our experimental breakthrough could provide us with critical information for universal understanding in fulleride.

Carbon powder derived from hypercoal (HPC) is obtained by treating carbon precursors prepared by precipitation with a stabilization and carbonization process. Its carbon powder was labelled SB- or B- based on the type of HPC raw material (sub-bituminous or a bituminous) and the carbonization temperature. The specific surface area of the carbon powder (SB-900) obtained by heat-treating a carbon precursor manufactured from sub-bituminous coal (mainly used as boiler fuel) at 900 °C was found to be 737 m²/g. In contrast, the specific surface area of carbon powder (B-900) obtained by heat-treating a carbon precursor manufactured from bituminous coal (primaly used as a coke precursor) at 900 °C was found to be 400 m²/g. SB-900 showed a specific surface area of approximately 1.8 times greater than that of B-900. Furthermore, it was confirmed that the structure primarily consist of microporous pores. When SB-900 and B-900 were applied as electrode materials in electric double-layer capacitors (EDLCs), electrodes made from SB-900 were found to exhibit higher capacitance than those made from B-900 or commercially available activated carbon (YP-50F). Examining the factors contributing to this, based on the chemical composition of the starting materials and the amount of oxygen-containing functional groups as determined by temperature-programmed desorption (TPD) measurements, revealed that factors other than oxygen-containing functional groups significantly affected SB-900 and B-900. A detailed examination of the pore characteristics using Ar adsorption measurements showed that the pore size distribution of the HPC-derived carbon powder exhibited a peak at 0.46 nm when analyzed using the Horvath-Kawazoe method. The differential pore volume increased in the vicinity of this peak. Since the pores were similar in size to the ions in the sulfuric acid electrolyte used to evaluate the EDLC characteristics, it was inferred that the powder would demonstrate higher capacitance than commercially available activated carbon and be suitable for use in EDLCs with an aqueous electrolyte. Additionally, increased adsorption was observed at 0.6 nm or less for SB-900 compared to B-900. It is suggested that SB-900 contains a higher proportion of ultramicropores (0.7 nm or less) within its micropores than B-900.

Temperature dependence of electrical resistivity of Rb₆C₆₀ in bulk was successfully detected using airtight cell under dry condition. Although the temperature dependence of electrical resistivity was qualitatively consistent with the band insulating character based on the rigid band model, the resistivity and the transport gap showed small values. In addition, the temperature dependence of electrical resistivity did not reproduce typical Arrhenius model in the wide temperature range, in contrast to characteristic of general insulators. It implies that the effect of electron-electron and electron-phonon interaction is not negligible in the highly electron doped C₆₀ system.

Resorcinol-Formaldehyde (RF) gels exhibit a dynamic variation of micropore properties upon carbonization, which is correlated with the structural reorganization from a crosslinked polymer network to amorphous carbon matrix. Understanding the micropore evolution during the carbonization of RF gels in association with the underlying mechanism is conducive to the control of pore properties for RF-derived carbon materials utilized for various applications, such as Na-ion battery anodes. In this study, the thermogravimetric technique combined with evolved gas analysis and the gas sorption measurements using N₂ and CO₂ have been employed to investigate the pyrolysis and carbonization behavior of the macroporous RF monolith prepared by the sol–gel process accompanied by phase separation. It is proposed that the micropore evolution commences at ~400 °C in the second pyrolytic step and continues up to ~900 °C at the end of the third pyrolytic stage. Micropores in the RF-derived carbon gradually decrease at elevated temperatures up to ~1400 °C. The drastic reduction of micropores takes place between 1400 °C and 1600 °C probably due to the narrowing of micropore windows, rendering the micropores “closed” to N₂ and CO₂ molecules.

Anion exchange resins are widely used to remove phosphate from water, but they have problems such as high costs and difficulty in reuse. In this study, we attempted to increase the quaternary nitrogen (N-Q) in activated carbon by impregnating pinecone with urea and zinc chloride and activating them at 600°C to improve the adsorption performance of phosphate ion. The sample using a mixture of pinecone, urea, and zinc chloride in a weight ratio of 1:4:1, which is Ur4-1, achieved the highest amount of 0.29 mmol/g for phosphate adsorption. Additionally, as the weight ratio of urea in the raw materials rose, the amount of N-Q of the samples showed an increasing tendency, whereas the specific surface area of the samples showed a decreasing tendency. This result suggests that the effect of N-Q content of the samples on phosphate ion adsorption performance is greater than that of specific surface area, which is a general indicator of the adsorption capacity of activated carbon. Ur4-1, which contained the largest amount of 1.81 wt% N-Q in this study and had good phosphate ion adsorption performance, was investigated for the amount of phosphate ion adsorption at equilibrium pH (pH_e) 2-10. As a result, the amount of phosphate ion adsorption for Ur4-1 was 0.051 mmol/g higher than that of commercial anion exchange resin, IMAC HP555, at pH_e 3.

Large quantities of woody pruning residues from Prunus mume (Japanese apricot) are generated annually through orchard management, yet they remain underutilized despite their renewable and lignocellulosic nature. In this study, pruned branches of Prunus mume were employed as a novel biomass precursor for the production of activated carbon via chemical activation with potassium hydroxide (KOH). The influence of impregnation ratio on the pore structure and surface area of the resulting carbons was systematically investigated. The optimal sample exhibited a high BET surface area of 2389.0 m²/g and well-developed microporosity. Phenol was selected as a model pollutant to assess adsorption performance. The branch-derived activated carbon demonstrated a maximum phenol adsorption capacity of 285.9 mg/g, which is approximately 1.7 times higher than that of a coal-based activated carbon (171.4 mg/g) and about 1.2 times higher than that of a coconut shell activated carbon (232.6 mg/g). Moreover, the material achieved adsorption equilibrium within one hour, indicating superior kinetics. These findings highlight the feasibility of converting fruit tree pruning waste into high-performance activated carbon.

This report presents a simple, low-cost thermal chemical vapor deposition method using alcohol as a carbon source for producing micron-sized carbon nanowalls (CNWs) on spherical carbon particles. The obtained CNWs have structural disorder and defects, as indicated by a low I_G/I_D (the ratio of the D-band peak to the G-band peak) ratio in the Raman spectrum. It is worth noting that the height and width of the CNWs reach approximately 10 µm, making them larger than previously reported CNWs. CNWs are produced at 730°C when using a tungsten mesh heater, while submicron-sized amorphous carbon grains are produced with a tungsten plate heater. However, CNWs are not produced at 800°C, even with a tungsten mesh heater. The reason why CNWs are not produced at 800°C remains unclear; however, their growth at 730°C is attributed to the preferential production of sp² carbon.