Resorcinol–formaldehyde (RF) gels exhibit drastic changes in micropore properties during carbonization, which are closely related to the structural transformation from a crosslinked polymer network to an amorphous carbon matrix. Understanding the micropore evolution during RF gel carbonization and the underlying mechanisms is essential for controlling the pore characteristics of RF-derived carbon materials for various applications, such as Na-ion battery anodes. In this study, thermogravimetric analysis coupled with evolved gas analysis as well as N₂ and CO₂ gas sorption measurements were performed to investigate the pyrolysis and carbonization behavior of macroporous RF monoliths prepared by the sol–gel process accompanied by phase separation. It is proposed that micropore evolution begins at ∼400 °C after the initial pyrolysis step at 150–300 °C, and continues up to ∼900 °C. The number of micropores in RF-derived carbon gradually decreases at higher temperatures up to ∼1400 °C. A drastic reduction in micropore volume occurs between 1400 °C and 1600 °C probably due to the narrowing of micropore windows, rendering the micropores “closed” to N₂ and CO₂ molecules.

The temperature dependence of the electrical resistivity of bulk Rb₆C₆₀ was measured using an airtight cell under dry conditions. Although the observed dependence was qualitatively consistent with the band insulating character based on a rigid band model, both the resistivity and the transport gap were relatively small. Moreover, over a wide the temperature range, the resistivity did not follow the typical Arrhenius model. This suggests that electron-electron and electron-phonon interactions play an important role in the highly electron doped C₆₀ system.

Among C₆₀ compounds, A₆C₆₀ (A=alkali metal) is considered to be an insulator because the lowest molecular orbital is fully filled. Although C₆₀ compounds have been studied extensively for many years, the physical properties of A₆C₆₀ have not been investigated because of experimental difficulties. We have now detected the temperature dependence of the electrical resistivity of K₆C₆₀ in bulk under dry conditions. Contrary to expectation, the experimentally estimated value of E_g was significantly smaller than those given in previous reports. In addition, the thermal activation behavior did not obey either the Arrhenius law or variable range hopping models over the temperature range. We attribute this anomalous behavior to the effect of lattice dynamics. The resistivity data obtained in our experimental breakthrough can provide us with critical information for a universal understanding of fullerides.

The effect of MnO₂ crystallinity on the performance of lithium–oxygen batteries (LOBs) was investigated. Low- and high-crystallinity MnO₂ samples (LC-MnO₂ and HC-MnO₂) were synthesized and used to fabricate positive electrodes incorporating activated carbon aerogels (ACAs). In this configuration, the ACA provided a high-surface-area, acting as an electronically conductive support that serves as a substrate for Li₂O₂ deposition and facilitates efficient electron transport to the MnO₂ catalyst. Structural analyses demonstrated that LC-MnO₂ had broader X-ray diffraction peaks and a larger surface area than HC-MnO₂, indicating lower crystallinity and a higher oxygen vacancy density. According to the electrochemical measurements, the LC-MnO₂/ACA electrode provided lower charging voltages and markedly improved the cycling stability, sustaining approximately 70 more cycles than the HC-MnO₂/ACA electrode at a fixed capacity of 300 mAh g⁻¹. These improvements are attributed to the increased surface area and oxygen vacancies, which facilitate Li⁺ insertion and promote Li₂O₂ formation on the catalyst surface. In addition to the high-surface-area and an electronically conductive ACA support, these findings highlight the crucial role of crystallinity in both the discharge and charge reactions in LOBs, demonstrating that low-crystallinity MnO₂ is a promising catalyst for improving the overall battery performance.

Direct quantitative evidence is provided that hydroxyl radicals (•OH) play a significant role in the degradation of Fe–N–C catalysts during the oxygen reduction reaction under specific electrochemical conditions. Using a radical trapping method with coumarin, we demonstrated 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 validation of the long-hypothesized •OH-driven degradation path in non-precious metal catalysts. In contrast, at 0.8 V, degradation proceeded despite negligible •OH formation, suggesting alternative paths such as oxidative Fe demetallation or nitrogen species modification. Post-degradation structural analyses supported this interpretation, revealing potential-dependent increases in surface oxygen content, partial oxidation of nitrogen species, and a reduction in Fe–N_x site abundance. Collectively, these results underscore the condition-dependent and multifactorial nature of Fe–N–C catalyst degradation and provide mechanistic insights for improving their durability in fuel cell applications.

The chemical reactivity of carbon materials is primarily governed by edge sites; nevertheless, this reactivity may also depend on the energy levels of π-electrons, especially the Fermi level. This hypothesis can be verified by conducting experiments using carbon materials with consistent structural and functional group compositions, while varying only the Fermi level. We prepared carbon thin films with thicknesses of several nanometers by chemical vapor deposition on Al₂O₃ nanoparticles. The structure, quantity, and quality of the edge sites in the carbon films remained constant regardless of the number of carbon layers, except for a single layer. However, the work function measurements indicated that the Fermi level varied with the number of carbon layers. When cobalt was supported on these carbon thin films and its reduction and carbonization behavior were examined, the composition of the cobalt species changed with the number of carbon layers. These results reveal that the Fermi level of carbon influences the chemical reactivity between the carbon support and cobalt, thereby offering novel insights into the potential for tuning the reactivity of carbon materials by controlling the Fermi level.

Single-walled carbon nanotubes (CNTs) have emerged as promising metal-free catalysts for oxygen reduction reactions in microbial fuel cells because of their high electrical conductivity and structural tunability. CNTs were co-doped with nitrogen and sulfur (N,S-CNTs) through a pyrolysis route using thiourea after an oxidative acid treatment, which helped introduce defects and anchoring sites. The results of X-ray photoelectron spectroscopy confirmed the successful incorporation of pyridinic-N, pyrrolic-N, and thiophenic-S species, whereas Raman spectroscopy revealed increased structural disorder without compromising the integrity of the CNT framework. In an electrochemical test in alkaline media, N,S-CNTs had an onset potential of 0.82 V vs. a standard hydrogen electrode and an electron transfer number approaching 3.6, indicating increased activity and selectivity in oxygen reduction reactions compared to pristine and N-doped CNTs. Furthermore, in a chronoamperometric stability test, N,S-CNTs showed minimal performance degradation over 6 h. When used as a cathode material in a single-chamber microbial fuel cell, N,S-CNTs achieved a peak power density of 126 mW/m², more than twice that of an undoped benchmark cathode, while also exhibiting lower area-specific resistance. These results highlight that the N,S-co-doping of CNTs improves their catalytic efficiency and durability in the oxygen reduction reaction in microbial fuel cells.

A simple, low-cost thermal chemical vapor deposition method is reported for the production of micron-sized carbon nanowalls (CNWs) on spherical carbon particles using ethyl alcohol as a carbon source. The resulting CNWs had structural disorder and contained many defects, as indicated by the low I_G/I_D ratio (the ratio of the G band to D band peaks) in the Raman spectrum. The CNWs had heights and widths of approximately 10 µm, making them larger than previously reported CNWs. Using a tungsten mesh heater, they were produced at 730 °C, whereas submicron-sized amorphous carbon were produced with a tungsten plate heater. However, CNWs were not produced at 800 °C, even when using the tungsten mesh heater. The reason for the latter is unclear, while the growth at 730 °C is attributed to the preferential formation of sp²-bonded carbon.