Pentagons and Heptagons on Edges of Graphene Nanoflakes Analyzed by X-ray Photoelectron and Raman Spectroscopy

Nanoarchitectonics for Pentagon Defects in Carbon: Properties and Catalytic Role in Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a crucial process in electrochemical energy technologies, featuring fuel cells and metal-air batteries in the coming carbon-neutral society. Carbon materials have garnered significant attention as economical, sustainable alternatives to precious metal catalysts. In particular, there have been increasing reports recently that pentagons introduced into graphitic carbons promote catalytic activity for ORR. In addition, interesting studies are reported on carbon materials' synthesis, characterization, and spin polarization properties with pentagonal defects. This review comprehensively summarizes the formation mechanism, characterization, spin, oxygen (O2) adsorption, and ORR catalytic activity of carbon catalysts with pentagonal defects. By connecting the dots between theoretical insights and experimental results, this review elucidates the fundamental principles governing pentagon-related activity and offers perspectives on future directions for designing efficient ORR catalysts based on carbon materials.

Physical Adsorption and Raman Spectra of Hydrazine Hydrate on the Graphene Surface

In experimental studies, hydrazine hydrate is widely employed as a reducing agent for the conversion of graphene oxide to graphene. Herein, we conducted theoretical calculations using cluster models to investigate the adsorption behavior of hydrazine hydrate on the surface of graphene. The calculated adsorption energy reveals that hydrazine hydrate can physically bind to the graphene surface. Our findings indicate that two hydrogen bonds stabilize the hydrazine hydrate molecule, while its adsorption onto the graphene surface is primarily driven by van der Waals forces. By combining computational simulations and experimental measurements, we thoroughly examined the Raman spectra of both free and adsorbed hydrazine hydrates, which enabled us to gain detailed insights into their molecular vibrations. Notably, in the Raman spectra of free hydrazine hydrate, a strong peak at around 3300 cm-1 corresponds to the NH2 vibration. Similarly, peaks near 3300 cm-1 were observed in the Raman spectra of graphene with adsorbed hydrazine hydrate molecules. The results are expected to provide valuable references for future experimental investigations involving hydrazine hydrate.

Spectroscopic Differentiation of Structural Transitions from Carbon Nanobelts to Carbon Nanotubes

In this study, simulated X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to differentiate the early stage structures as carbon nanobelts (CNBs) evolved into carbon nanotubes (CNTs). The effects of edge type, length, and diameter on the spectroscopic characteristics of armchair and zigzag CNTs were examined. Variations in XPS spectra were found to correspond to changes in the bandgap, while Raman spectra provided distinct bands associated with specific structural features. Notably, in armchair CNTs, the C 1s XPS peak positions exhibited clear differences depending on the structure. Additionally, the Kekulé vibration band and other characteristic bands in Raman spectra varied with length and diameter, enabling differentiation of armchair CNT structures. Although the structural analysis of zigzag CNTs was challenging using XPS, Raman spectroscopy proved to be effective in distinguishing structural differences. This study lays the groundwork for future spectroscopic analyses, contributing to the broader understanding of nanocarbon materials such as CNBs and CNTs and their potential applications in advanced electronic materials.

Unveiling Structural Variations in Armchair-Edge Coronoids by Spectroscopies

This study explores the electronic and vibrational properties of armchair coronoids (ACs), a unique class of polycyclic aromatic hydrocarbons with varying molecular and cavity sizes. Through density functional theory simulations, we investigated the X-ray photoelectron spectroscopy (XPS) and Raman spectra of C222, C114, C42, and their derivatives with different cavity sizes. The results reveal that band gaps and electronic properties of ACs can be precisely tuned by adjusting the molecular and cavity dimensions. XPS spectra demonstrated shifts in binding energy correlating with bandgap variations, while Raman spectra exhibited distinct C-C stretching and breathing modes. Notably, the introduction of cavities led to shifts in the breathing mode band, providing insights into the structural identification of ACs through Raman spectroscopy. The findings suggest that combining XPS and Raman spectroscopy can effectively characterize ACs, offering a comprehensive understanding of their structure-property relationships. This research lays the groundwork for future experimental and theoretical studies on the potential applications of ACs in electronic materials.

Poly(vinylalcohol) (PVA) Assisted Sol-Gel Fabrication of Porous Carbon Network-Na3V2(PO4)3 (NVP) Composites Cathode for Enhanced Kinetics in Sodium Ion Batteries

Na₃V₂(PO₄)₃ is regarded as one of the promising cathode materials for next-generation sodium ion batteries, but its undesirable electrochemical performances due to inherently low electrical conductivity have limited its direct use for applications. Motivated by the limit, this study employed a porous carbon network to obtain a porous carbon network–Na₃V₂(PO₄)₃ composite by using poly(vinylalcohol) assised sol-gel method. Compared with the typical carbon-coating approach, the formation of a porous carbon network ensured short ion diffusion distances, percolating electrolytes by distributing nanosized Na₃V₂(PO₄)₃ particles in the porous carbon network and suppressing the particle aggregation. As a result, the porous carbon network–Na₃V₂(PO₄)₃ composite exhibited improved electrochemical performances, i.e., a higher specific discharge capacity (~110 mAh g⁻¹ at 0.1 C), outstanding kinetic properties (~68 mAh g⁻¹ at 50 C), and stable cyclic stability (capacity retention of 99% over 100 cycles at 1 C).