Unraveling the Catalytic Graphitization Mechanism of Ni-P Electroless Plated Cokes via In Situ Analytical Approaches.

We elucidate the catalytic graphitization mechanism using in situ analytical approaches. Catalytic graphitization is achieved through a Ni-P electroless plating process at a relatively low temperature of 1600 °C, which allows for a high crystallinity of coke. We also employ an ultrasonic treatment during the Ni-P electroless plating stage to effectively form metal layers on the surface. The impact of the ultrasonic treatment on the Ni-P electroless plating is confirmed by field emission scanning electron microscopy images of the cross-section and an elemental composition analysis using energy dispersive X-ray spectroscopy mapping. Structural analysis of the graphitized cokes via X-ray diffraction (XRD) and Raman spectroscopy shows that Ni-P electroless plating significantly accelerates the graphitization process. Furthermore, we illuminate the graphitization behavior through in situ transmission electron microscopy and XRD analysis. Nickel layers on the coke surface facilitate graphite formation by encouraging the dissolution and precipitation of amorphous carbons, thus resulting in efficient graphitization at a relatively low temperature.

2D Materials Beyond Post-AI Era: Smart Fibers, Soft Robotics, and Single Atom Catalysts.

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs), which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AI era. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.

A Graphene-Based Polymer-Dispersed Liquid Crystal Device Enabled through a Water-Induced Interface Cleaning Process.

We report the use of four-layer graphene (4LG) as a highly reliable transparent conductive electrode (TCE) for polymer-dispersed liquid crystal (PDLC)-based smart window devices. The adhesion between 4LG and the substrate was successfully improved through a water-induced interface-cleaning (WIIC) process. We compared the performance of a device with a WIIC-processed 4LG electrode with that of devices with a conventional indium tin oxide (ITO) electrode and a 4LG electrode without a WIIC. With the application of the WIIC process, the PDLC smart window with a 4LG electrode exhibited reduced turn-on voltage and haze compared to 4LG without the WIIC process and characteristics comparable to those of the ITO electrode. The WIIC-processed 4LG electrode demonstrated enhanced electrical properties and better optical performance, leading to improved device efficiency and reliability. Furthermore, our study revealed that the WIIC process not only improved the adhesion between 4LG and the substrate but also enhanced the compatibility and interfacial interactions, resulting in the superior performance of the smart window device. These findings suggest that 4LG with WIIC holds great promise as a transparent conductive electrode for flexible smart windows, offering a cost-effective and efficient alternative to conventional ITO electrodes.

Boron-Doped Edges as Active Sites for Water Adsorption in Activated Carbons.

Investigating the surface properties of heteroatom-doped carbon materials is essential because these versatile materials have found use in a variety of energy and environmental applications; an understanding of these properties would also lead to an improved appreciation of the direct interaction between the reactant and the functionalized surface. Herein, we explore the effect of boron (B) doping on the surface properties of activated carbon (AC) materials based on their water adsorption behavior and oxygen reduction reaction. In the high-temperature B doping process, B-doped AC materials at 1400 °C exhibit an open pore structure with B-O bonds, whereas at a temperature of 1600 °C, a nonporous structure containing a large amount of B-C bonds prevails. The B-O species act as active sites for water adsorption on the carbon surface. On the basis of the isothermal adsorption heat, we suggest that B atoms are present at the pore openings and on the surfaces. The B-O moieties at the open edges improve the electrocatalytic activity, whereas the B-C bonds at the closed edges decrease the electrocatalytic activity because of the stable structure of these bonds. Our findings provide new evidence for the electrocatalytic properties associated with the structure of B-doped edges.

Thermodynamics of Linear Carbon Chains.

Linear carbon chains (LCCs) are one-dimensional materials with unique properties, including high Debye temperatures and restricted selection rules for phonon interactions. Consequently, their Raman C-band frequency's temperature dependence is a probe to their thermal properties, which are well described within the Debye formalism even at room temperatures. Therefore, with the basis on a semiempirical approach we show how to use the C band to evaluate the LCCs' internal energy, heat capacity, coefficient of thermal expansion, thermal strain, and Grüneisen parameter, providing universal relations for these quantities in terms of the number of carbons atoms and the temperature.

Quantifying Carbon Edge Sites on Depressing Hydrogen Evolution Reaction Activity.

To understand the effect of microstructural characteristics of carbon materials on their electrochemical or electrocatalytic performance, an in-depth study of the edges in carbon materials should be carried out. In this study, catalytically grown platelet-type carbon nanofibers (CNFs) with fully exposed edges were physically and chemically passivated to clarify the relationship between the edge density and the hydrogen evolution reaction (HER) activity. Due to the aligned structure along the fiber axis, the edges on the outer surface of the CNFs were easily modified without using a complex process. The edges on the surface of the CNFs were inactivated by sequentially forming single, double, and multiple loops as the heat treatment temperatures increased. The number of edges within the CNFs was quantitatively measured using temperature-programmed desorption (TPD) up to 1800 °C. The surviving edges on the surface of thermally treated CNFs were identified by chemical functionalization via an amination reaction. We identified a close relationship between the HER activity and the edge density. When evaluating the electrochemical and electrocatalytic activity of carbon materials, it is important to know the portion of the edge surface area with respect to the total surface area and edge ratio.

Enriched Pyridinic Nitrogen Atoms at Nanoholes of Carbon Nanohorns for Efficient Oxygen Reduction.

Nitrogen (N)-doped nanostructured carbons have been actively examined as promising alternatives for precious-metal catalysts in various electrochemical energy generation systems. Herein, an effective approach for synthesizing N-doped single-walled carbon nanohorns (SWNHs) with highly electrocatalytic active sites via controlled oxidation followed by N2 plasma is presented. Nanosized holes were created on the conical tips and sidewalls of SWNHs under mild oxidation, and subsequently, the edges of the holes were easily decorated with N atoms. The N atoms were present preferentially in a pyridinic configuration along the edges of the nanosized holes without significant structural change of the SWNHs. The enriched edges decorated with the pyridinic-N atoms at the atomic scale increased the number of active sites for the oxygen reduction reaction, and the inherent spherical three-dimensional feature of the SWNHs provided good electrical conductivity and excellent mass transport. We demonstrated an effective method for promoting the electrocatalytic active sites within N-doped SWNHs by combining defect engineering with the preferential formation of N atoms having a specific configuration.