Yuta Nabae

Double gyroid-structured porous carbons are attractive because their bicontinuous networks provide efficient transport pathways. However, the fabrication of such structures remains challenging owing to the narrow compositional window of the double gyroid phase and the difficulty in preserving the morphology during carbonization. In this study, nitrogen-doped mesoporous carbon (NMC) with a double gyroid structure was fabricated through the self-assembly of poly(4-vinylpyridine)- block -poly(2,2,2-trifluoroethyl methacrylate) (P4VP- b -PTFEMA) and phenol-formaldehyde resol. By systematically varying the resol content, morphology transitions from lamellar to double gyroid and cylindrical structures were observed, enabling access to the otherwise narrow double gyroid-forming region. The double gyroid morphology was retained after carbonization at 900 °C, yielding NMCs with ordered bicontinuous nanostructures. Furthermore, the optimized composition was scaled up while maintaining the double gyroid framework, yielding a mesoporous NMC with a pore diameter of 7.1 nm. More importantly, the results of the present study demonstrate that the selective incorporation of low-molecular-weight resol can effectively manipulate the self-assembled morphology of block copolymer systems, enabling access to the double gyroid phase and stabilization of the bicontinuous nanostructure during carbonization. These findings provide new insights into morphology control in block copolymer/additive systems and demonstrate how self-assembled polymer nanostructures can be translated into complex porous carbon architectures.

One of the alternatives to platinum catalysts for the cathode of polymer electrolyte fuel cells is transition metal oxide-based catalysts, such as TiO _x , ZrO _x , and NbO _x . Although these catalysts have been considered for their potential because of their high chemical stability under acidic conditions, their low oxygen reduction reaction (ORR) activity requires significant improvement. A contributing factor to this low activity is the poor conductivity of oxides. To improve this, it is believed necessary to control the crystal phase, the size of the oxides, and the local conduction paths near the oxide particles. Generally, it is difficult to separate and discuss these factors independently, making it unclear which factor is the most influential. In this study, niobium oxide nanoparticles with significantly different sizes were synthesized using either the irradiation method or impregnation method for the preparation of catalysts precursors, followed by heat treatment. Here, we report on the comparison of ORR activity, focusing on the differences in the size of the niobium oxide nanoparticles in the catalyst. The irradiation method is a simple one-pot process, in which a glass vial containing ultra-pure water together with conductive carbon nanopowder and metal source (Nb ₂ (C ₂ O ₄ ) ₅ ) are irradiated with gamma-ray from a cobalt-60 source. The impregnation method places conductive carbon nanopowder and the metal source in ethanol, followed by a drying process to obtain the sample. Thus-prepared composite nanoparticles, acquired in powder form, were used as precursors. Polyacrylonitrile was added and the mixture was heat-treated in an ammonia atmosphere to prepare the catalyst. It is expected that polyacrylonitrile will be graphitized upon heat treatment, forming local conduction paths near the oxide particles. These samples were characterized by the techniques of TEM, XRD, and LSV. When the precursor prepared by the irradiation method was heat-treated, TEM observation revealed that the Nb-based nanoparticles on the surface of the carbon support had a particle size of 7 nm (Figure 1 (a)). Following heat treatment of the impregnation-prepared precursor, the size of the Nb-based nanoparticles on the surface of the support was 13 nm (Figure 1 (b)), indicating that each method of precursor preparation successfully produced Nb-based nanoparticles of different sizes. In both cases, XRD showed diffraction patterns corresponding to niobium oxynitride. Additionally, composition ratios of niobium oxynitride determined from Vegard’s law, assuming NbO _x N _{1- x} , were consistent regardless of the precursor preparation method. These catalytic activities were evaluated using Linear Sweep Voltammetry in an acidic medium, based on the open circuit potential in oxygen and current density. After heat-treating the irradiation-prepared precursor, the open circuit potential and current density were slightly higher compared to the impregnation method; however, no significant difference was observed. Using a model based on several assumptions, it was suggested that the dominant factor affecting ORR activity is not the size of the metal oxide nanoparticles, but the length of the local conduction paths near the oxide nanoparticles. The present study revealed that the ORR activity in niobium oxide nanoparticle catalysts does not significantly depend on the size of the oxide nanoparticles. [Acknowledgments] The authors thank Koga Isotope Co. Ltd. for their cooperation with the gamma-ray irradiation. XAS experiments were performed at the NW-10A beamline of KEK under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2022G074). This study was supported by JSPS KAKENHI (Grant Nos. 23K04912 and 24KJ1592). Figure 1: TEM images of the samples obtained from heat treatment of the precursor prepared by the (a) irradiation method and (b) impregnation method. Figure 1

Single-atom catalysts (SACs) possessing well-defined active sites of singular metal atoms have gained prominence in the field of electrocatalysis as they can be tuned to enhance activity and stability. In this study, a critical-raw-material (CRM)-free SAC is synthesized for the oxygen reduction reaction (ORR) by pyrolyzing polyimide nanoparticles and Fe without using a sacrificial template. While this pyrolyzed catalyst contains both of Fe nano-particles and atomically dispersed Fe centers, which was denoted as Fe(SA+Nano), the catalyst after magnetic purification (Fe(SA)/PI) is a single-atom catalyst without Fe nanoparticles, as proven by electronmicroscopy and X-ray absorption spectra, The resulting catalyst (Fe(SA)/PI) demonstrates outstanding performance as cathodes in proton-exchange membrane fuel cells (PEMFCs) and anion-exchange membrane fuel cells (AEMFCs) owing to sufficiently stabilized Fe single-atoms at the FeN ₄ sites. Figure 1

Nitrogen-doped mesoporous carbons (NMCs) are widely studied for their excellent electrical conductivity, chemical stability, and tunable pore structures. These properties make them promising materials for applications such as electrocatalysis. One common fabrication method is the hard-template method, which uses mesoporous silica as a structural template. However, this approach requires strong acids or bases, such as hydrofluoric acid or sodium hydroxide, to remove the template. This makes the process complex and less efficient. To overcome these challenges, the soft-template method has been developed. This method utilizes the self-assembly of block copolymers, which undergo microphase separation to form periodic nanostructures. By introducing a crosslinker, the morphology can be preserved during carbonization, allowing for the fabrication of well-defined mesoporous carbon ¹ . In this study, we designed a soft-template system based on poly(4-vinylpyridine)- block -poly(2,2,2-trifluoroethyl methacrylate) (P4VP- b -PTFEMA). P4VP and PTFEMA exhibit strong phase separation, enabling precise control over the domain size. Additionally, P4VP serves as both a nitrogen source and a stabilizing domain when crosslinked with phenol-formaldehyde resol ² . Unlike commercially available block copolymers, this system allows direct control over the polymer composition, enabling precise tuning of the pore size by adjusting the molecular weight. Additionally, since P4VP inherently contains nitrogen, there is no need to introduce an additional nitrogen precursor to achieve nitrogen doping. To fabricate NMCs, blend samples of P4VP- b -PTFEMA and resol were prepared and thermally treated at 900 °C. As shown in Figure 1, adjusting the molecular weight of PTFEMA allowed precise control over the pore size, ranging from 6.2 nm to 21 nm. In the presentation, we will also discuss the electrochemical oxygen reduction reaction using these NMCs and their potential as electrocatalysts. [Reference] 1. L. Gao, A. Chandra, Y. Nabae, T. Hayakawa, Polym. J. 2018 , 50 , 389. 2. Y. Kong, H. Kawahara, R. Kikuchi, N. Ohta, A. Mufundirwa, T. Hirai, K. Hatakeyama-Sato, Y. Nabae, T. Hayakawa, Polymer 2025 , 320 , 128098. [Acknowledgement] This study was financially supported by JSPS-KAKENHI(21K04828). Figure 1

Objectives : We report the development and practical evaluation of a cobalt/nitrogen-doped carbon (Co/N/C) catalyst for use in membrane electrode assemblies (MEAs) in proton exchange membrane fuel cells (PEMFCs). This study focuses on the long-term performance of the catalyst under realistic air-fed operation conditions, highlighting its potential as a durable and non-platinum alternative for cathode applications. Methods: The Co/N/C catalyst was synthesized from a cobalt-containing polyimide precursor via ammonia pyrolysis. The material was characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, and CHN elemental analysis. MEAs were fabricated with the synthesized catalyst as the cathode. Electrochemical performance was evaluated under air at 80 °C using Nafion NR211 membranes, in order to assess the practical durability and activity of the catalyst. Results and Conclusion: The synthesized material exhibited a high specific surface area (~2000 m²/g) and nitrogen-rich porous carbon characteristics. The MEAs maintained stable voltage over 400 hours at current densities of 0.1 and 0.2 A/cm², demonstrating the long-term operational stability of the catalyst. Polarization curves revealed a peak power density of approximately 411 mW/cm² at a current density of around 1000 mA/cm². At 500 mA/cm², the IR-corrected voltage was approximately 620 mV, while the IR-included voltage decreased to around 530 mV, indicating a notable impact of internal resistance. After an initial stabilization period, the cell voltage remained stable beyond 100 hours of continuous operation, further confirming the robustness of the catalyst under air-fed conditions. These findings underscore the feasibility of Co-based catalysts as practical alternatives to platinum in acidic PEMFC environments. Figure 1

Introduction Carbon flowers, a unique class of porous carbon materials, have garnered significant attention due to their intricate hierarchical structure composed of intersecting sheets on the particle surface, different from conventional micropores or mesopores. Owing to the open structure and improved surface area, carbon flowers have demonstrated outstanding performance in electrocatalyst, supercapacitor and gas capture. However, only a limited number of synthesis methods have been developed to achieve this unique morphology. In this study, we report a unique synthetic route for poly(amic acid) (PAA) flower-like particles (FLPs) as precursors for carbon flowers. A semiaromatic PAA (denoted as DA-6), comprising alternating rigid aromatic and flexible alkyl segments, was specifically designed to undergo precipitation polymerization with pyromellitic anhydride (PMDA). While conventional solvothermal methods have been reported to produce polyimide (PI) FLPs by heating the precursor of PAA solution, the PAA FLPs in this study formed spontaneously during precipitation polymerization at room temperature, representing the first reported FLPs in the form of PAA. Our findings provide a facile strategy for synthesizing carbon flowers from PAA FLPs and offer new insights into the self-assembly behavior of PAA via polycondensation. Results and Discussion The precipitation polymerization of DA-6 and PMDA was performed in the mixed solvent of cyclohexanone and acetone. The particle size of these FLPs was tunable by adjusting the mixed solvent ratio (Fig. 1a). Structural characterization using small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and polarized optical microscopy (POM) revealed that the flower-like morphology originated from the microcrystalline structure formed by the folding and stacking of PAA precursors (Fig. 1b). Solubility played a crucial role in determining crystallization rates and growth mechanisms. Under low-solubility conditions and vigorous stirring, PAA molecules randomly attached to existing lamellae, promoting branched lamellar growth, and resulting in larger particle sizes. The flower-like morphology was well preserved following thermal imidization and carbonization (Fig. 1c), although particle size shrinkage was observed in the carbon flowers. Cross-sectional images (Fig. 1d) confirmed the inner hollow structure of the carbon flowers. The as-synthesized carbon flowers exhibited high catalytic activity and selectivity for the 2-electron electrochemical reduction of oxygen in an acidic electrolyte (Fig. 1e), attributed to their nitrogen content (2.72%) and the efficient mass transport enabled by their open flower-like morphology. Figure 1

Precise control of pore structures of nitrogen‐doped mesoporous carbon (NMC) is still challenging. In this study, we address this issue by developing a soft‐template approach based on the molecular design of block copolymers, enabling systematic tuning of nanostructures. Specifically, we synthesized poly(4‐vinylpyridine)‐ block ‐poly(2,2,2‐trifluoroethyl methacrylate) (P4VP‐ b ‐PTFEMA) via reversible addition–fragmentation chain‐transfer (RAFT) polymerization and employed it as a soft template for fabricating NMCs. The P4VP block selectively interacts with phenol‐formaldehyde resol, enabling retention of microphase‐separated morphology during carbonization, while the fluorine‐containing PTFEMA block enhances phase separation through strong segmental repulsion. Ordered morphologies, including cylindrical structures, are formed upon blending with resol. These morphologies are preserved during thermal treatment at 900°C, leading to the formation of NMCs with well‐defined porous structures. The resulting NMCs exhibit tunable pore diameters ranging from 5.5 to 21.3 nm, controlled by the degree of polymerization of the PTFEMA block. These results highlight the potential of block copolymer design for achieving predictable mesopore architectures, offering a scalable platform for the development of functional porous materials.