Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Synthesis of crown-ether-embedded graphene by the solution plasma International coauthorship

Kim H.m., Saito N., Kim D.w.

Carbon Vol. 216 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

DOI： 10.1016/j.carbon.2023.118578

A solid-solution approach for high frequency 3-dimensional isotropic negative-refractive-index metamaterials based on microwave ceramics International coauthorship Open Access

Chang Q., Wang Z., Liu X., Saito N., Fan T.

Ceramics International Vol. 50 ( 1 ) page： 772 - 780 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramics International

Negative refraction has yielded valuable insights and solutions in electromagnetics. However, progress in this field has been hindered primarily by implementation challenges, including the limited availability of raw materials and assembly difficulties, particularly at high frequencies. In this paper, a novel flexible self-assembly method was proposed, through which a controllable solid solution of close-packed structures can be attained. By integrating the flexible self-assembly method with an all-dielectric left-handed material structure, a negative-refractive-index metamaterial (NRIM) model was conceived. Magnetism is not a prerequisite under this scheme; therefore, a demonstration based on a microwave dielectric ceramic was proposed, wherein two subdivisions of close-packed structures were studied. Analysis of the field distribution and electromagnetic eigenmodes using finite element analysis revealed a negative refraction band at around 20 GHz, with a relative bandwidth of 4.2%. The analysis of dispersion behavior verified spatial isotropism in the NRIM. In summary, the designed passive NRIM only requires moderate dielectrics and is isotropic in three dimensions, thus bearing a high resemblance to natural mediums.

DOI： 10.1016/j.ceramint.2023.10.158

Regulated Phase Separation in Al–Ti–Cu–Co Alloys through Spark Plasma Sintering Process Open Access

Lee S., Chokradjaroen C., Sawada Y., Yoon S., Saito N.

Materials Vol. 17 ( 2 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al–Ti–Cu–Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al–Ti–Cu–Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8–5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

DOI： 10.3390/ma17020304

Conversion of fructose to 5-hydroxymethylfurfural using solution plasma process Reviewed International coauthorship

Klanarong N., Saito N., Prasertsung I., Damrongsakkul S.

Renewable Energy Vol. 218 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Renewable Energy

5-hydroxymethylfurfural (HMF), a key building block chemical derived from renewable lignocellulosic biomass, is used to produce a variety of derivatives for the biorefinery industry. In this work, the solution plasma process (SPP) was first applied to convert fructose, a key component from biomass, into HMF. Various conditions that affect fructose conversion and HMF yield were studied, including plasma treatment time (0–300 min), DMSO concentration (0–70%), electrode types (Iron; Fe and tungsten; W), system temperature (70–90 °C) and initial fructose concentration (10 g/L and 25 g/L). SPP was showed to enhance the conversion process to achieve high fructose conversion and HMF yield at the temperature (90 °C) lower than other conventional heating processes. The maximum fructose conversion and HMF yield were achieved at 95% and 76%, respectively at the DMSO concentration of 70% with Fe-electrodes, 90 °C of system temperature, 10 g/L of initial fructose concentration, 22.5 kHz of pulsed frequency and plasma treatment time of 240 min. Sulfuric acid formed from DMSO dissociation and Fe-nanoparticles from electrode erosion could effectively act as catalysts for the dehydration of fructose to HMF. SPP can be a high-potential tool for enhancing HMF production from the dehydration process in BCG economy.

DOI： 10.1016/j.renene.2023.119299

Highly durable graphene-encapsulated platinum-based electrocatalyst for oxygen reduction reactions synthesized by solution plasma process Reviewed

Park J.H., Kim K., Wang X., Huda M., Sawada Y., Matsuo Y., Saito N., Kawasumi M.

Journal of Power Sources Vol. 580 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Power Sources

Though expensive platinum (Pt) is used as catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), insufficient durability remains as a bottleneck for commercialization of PEFCs. Improving both catalytic performance and durability by graphene encapsulation is an attractive strategy to solve this problem. In this study, graphene-encapsulated PtFe core-shell catalyst is synthesized with dimethyl formamide (DMF) and a pair of Pt and Fe electrodes without using any metal salts by utilizing the solution plasma (SP) process. TEM and EELS results show synthesized PtFe nanoparticles are encapsulated with close to single-layered highly crystallized graphene. Although commercial Pt/C showed significant performance degradation (ECSA −33%, MA −68%) after 50,000 cycles of accelerated durability test (ADT), PtFe core-shell catalyst shows remarkably improved durability (ECSA −13%, MA −19%) while graphene shell clearly remains. The improved durability is more prominent in the single cell test, the decrease in maximum power density after 6000 cycles of ADT was significantly lower as −1.2%, compared to that of Pt/C (−52.1%). This study introduces a novel and attractive catalyst synthesis process by the SP method followed by heat treatments and suggests graphene encapsulation can improve long-term durability of catalyst while maintaining ORR activity.

DOI： 10.1016/j.jpowsour.2023.233419

Novel solution plasma synthesis of highly durable carbon shell encapsulated platinum-based cathode catalyst for polymer electrolyte membrane fuel cells Reviewed

Park J.H., Saito N., Kawasumi M.

Carbon Vol. 214 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Developing an effective method for synthesizing high-performance and durable catalysts for the oxygen reduction reaction is of great importance for cost reduction and the wide application of fuel cells. This study presents a simple and effective strategy using a plasma reaction in the liquid phase to synthesize carbon-shell-encapsulated Pt and PtFe catalysts. A carbon-shell-encapsulated PtFe catalyst alloyed with up to 29 at.% Fe exhibits a mass activity of 730 mA·mgpt−1 and a specific activity of 1772 μA cm−1, which are 2.4 and 5 times higher than that of commercial Pt/C, respectively. The carbon shell effectively maintained the low oxidation state of Pt by suppressing the formation of Pt–OH and significantly improved the durability of the catalyst in accelerated durability tests, increasing the gap in mass activity with Pt/C by a factor of up to six after 50,000 cycles. In addition, the decrease in the electrochemical surface area by the carbon shell enabled a more stable 4-electron reaction over a wide potential range. This study may provide fascinating insights into the effect of the carbon shell contributing to the improvement of the catalytic activity and durability of fuel cells as well as the novel plasma-based synthesis strategy of core-shell catalyst.

DOI： 10.1016/j.carbon.2023.118364

Preparation of lightweight, high hardness multi-component systems induced by partial oxidation and hard intermetallic phase formation Reviewed

Lee S., Chokradjaroen C., Sawada Y., Saito N.

Journal of Materials Research Vol. 38 ( 18 ) page： 4235 - 4246 2023.9

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Research

The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems were prepared by mechanical alloying in oxygen-lean atmosphere followed by spark plasma sintering. The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems which were sintered at 750 °C after 16 h milling showed the highest hardness of 509 and 947 HV with low densities of 2.9 and 3.9 g/cm3, respectively. The decrease in particle size and uniform dispersion of elements through optimization of the MA process induced the formation of uniform composite microstructure after SPS. Moreover, the addition of the fourth element, Cu, showed a significant impact on the improvement in hardness. This result was explained from the perspective of the microstructure and the electronic nature of elements. Our results provide a facile method for synthesizing oxide/metal composites from elemental powders without a separate oxidation process. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1557/s43578-023-01137-z

Cationic nitrogen-doped graphene coated silver as low-work function electrode for inverted perovskite solar cells Reviewed

Yokoyama K., Lin H.S., Shui Q.J., Wang X., Saito N., Matsuo Y.

Applied Physics Express Vol. 16 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Express

Interfacial layers (ILs) located between the cathode and electron transport layer (ETL) in inverted perovskite solar cells are commonly required to achieve high-performance devices. Therefore, it is essential to develop excellent IL materials to improve efficiency and stability. This paper introduces the graphene-based IL material, namely cationic nitrogen-doped graphene (CNG), and evaluates its performance on a methylammonium lead iodide (MAPbI3)-type inverted perovskite solar cells. The device with a CNG IL achieved a power conversion efficiency of 13.5%, which is higher than a state-of-the-art reference using bathocuproine IL. Mechanistic studies demonstrated that the CNG IL can (1) efficiently collect electrons from the lowest unoccupied molecular orbital of ETL by lowering the work function of the silver cathode, (2) improve the conductivity of the silver electrode for better electron transfer, and (3) smooth out the interface contact between ETL and cathode to reduce defects in the device. As a result, the CNG IL enhanced the inverted perovskite solar cells performance by simultaneously increasing the open-circuit voltage, short-circuit current density, and fill factor. Moreover, the unencapsulated CNG IL-applied device demonstrated good long-term stability, with 96% efficiency retained over 1000 h in nitrogen atmosphere at room temperature.

DOI： 10.35848/1882-0786/acea18

Introducing micropores into carbon nanoparticles synthesized via a solution plasma process by thermal treatment and their charge storage properties in supercapacitors Reviewed International coauthorship

Thu M.M., Chaiammart N., Jongprateep O., Techapiesancharoenkij R., Thant A.A., Saito N., Panomsuwan G.

RSC Advances Vol. 13 ( 24 ) page： 16136 - 16144 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Carbon materials synthesized via a solution plasma process (SPP) have recently shown great potential for various applications. However, they mainly possess a meso-macroporous structure with a lack of micropores, which limits their applications for supercapacitors. Herein, carbon nanoparticles (CNPs) were synthesized from benzene via SPP and then subjected to thermal treatment at different temperatures (400, 600, 800, and 1000 °C) in an argon environment. The CNPs exhibited an amorphous phase and were more graphitized at high treatment temperatures. A small content of tungsten carbide particles was also observed, which were encapsulated in CNPs. An increase in treatment temperature led to an increase in the specific surface area of CNPs from 184 to 260 m2 g−1 through the development of micropores, while their meso-macropore structure remained unchanged. The oxygen content of CNPs decreased from 14.72 to 1.20 atom% as the treatment temperature increased due to the degradation of oxygen functionality. The charge storage properties of CNPs were evaluated for supercapacitor applications by electrochemical measurements using a three-electrode system in 1 M H2SO4 electrolyte. The CNPs treated at low temperatures exhibited an electric double layer and pseudocapacitive behavior due to the presence of quinone groups on the carbon surface. With increasing treatment temperature, the electric double layer behavior became more dominant, while pseudocapacitive behavior was suppressed due to the quinone degradation. Regarding cycling stability, the CNPs treated at high temperatures (with a lack of oxygen functionality) were more stable than those treated at low temperatures. This work highlights a way of introducing micropores into CNPs derived from SPP via thermal treatment, which could be helpful for controlling and adjusting their pore structure for supercapacitor applications.

DOI： 10.1039/d3ra02314a

Morphological Evolution of Gold Nanoparticles Synthesized via Solution Plasma Sputtering: Effect of Sodium Chloride Concentration and Storage Time Reviewed International coauthorship

Chantaramethakul J., Choophun N., Chokradjaroen C., Watthanaphanit A., Saito N., Panomsuwan G.

Journal of Physical Chemistry C Vol. 127 ( 6 ) page： 3184 - 3193 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Morphological control of gold nanoparticles (AuNPs) is vital for tuning their optical, chemical, physical, and catalytic properties for desired specific applications. Despite numerous efforts dedicated in recent years, controlling the morphology of AuNPs synthesized via solution plasma sputtering (SPS) remains a challenge, requiring further investigation. Herein, AuNPs were synthesized via SPS in sodium chloride (NaCl) solutions of various concentrations (0.5, 1, 2, and 5 mM). Evolutions of localized surface plasmon resonance and morphology of AuNPs over a 30 day storage period were thoroughly examined using ultraviolet-visible spectroscopy and field-emission transmission electron microscopy. The formation and growth mechanisms of AuNPs during and after synthesis provide more insights into this nascent field. At the initial storage time, AuNPs with chain-like structures were observed at all the NaCl concentrations. Their size tended to increase from 6 to 10 nm with a broader size distribution with increasing NaCl concentration. At a prolonged storage time of 15 days, AuNPs became smaller and more isolated at all NaCl concentrations owing to the oxidative etching effect. After 30 days of storage, the number of Au ions dissolved from etching slowly reduced and grew on the AuNPs, affording increased particle sizes. The interplay between etching and growth processes proceeded until reaching equilibrium. AuNPs exhibited good colloidal stability at low NaCl concentrations (i.e., 0.5, 1, and 2 mM); however, coalescence and sedimentation occurred at a high NaCl concentration of 5 mM owing to a considerable reduction in the electrical double-layer thickness. These results demonstrated that the NaCl concentration and storage time crucially affect the morphological evolution and stability of AuNPs synthesized via SPS.

DOI： 10.1021/acs.jpcc.2c06474

A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment Reviewed International coauthorship

Back S., Saito N., Lee S.

Journal of Environmental Chemical Engineering Vol. 11 ( 1 ) 2023.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Environmental Chemical Engineering

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 ?s, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.

DOI： 10.1016/j.jece.2022.109075

Carbon Fibers Prepared via Solution Plasma-Generated Seeds Reviewed

Romero Valenzuela A.E., Chokradjaroen C., Choeichom P., Wang X., Kim K., Saito N.

Materials Vol. 16 ( 3 ) 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Materials

Carbon fibers are materials with potential applications for CO2 capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when organic precursors are used. During the discharge and formation of carbon materials in solution, a soot product-denominated solution plasma-generated seeds (SPGS) is simultaneously produced at room temperature and atmospheric pressure. Here, we propose a preparation method for carbon fibers with different and distinctive morphologies. The control over the morphology is also demonstrated by the use of different formulations.

DOI： 10.3390/ma16030906

Effect on percolation threshold of catalytic layer: Pt/N-Doped graphene shell onto SWCNT for ORR electrode Reviewed

Dechojarassri D., Wang X., Chae S., Sawada Y., Hashimoto T., Saito N.

Fuel Cells Vol. 23 ( 1 ) page： 4 - 14 2023.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Fuel Cells

A high-rate oxygen reduction reaction (ORR) is necessary for polymer electrolyte membrane fuel cells (PEMFC). In this work, by using a solution plasma technique, Pt catalytic particles coated with N-doped graphene (Pt-NG) were effectively produced at 25°C. According to transmission electron microscope images, the average diameter of Pt particles was 4 nm, while the graphene layer thickness was less than 1 nm. A catalytic layer of Pt-NG supported on single-walled carbon nanotubes (Pt-NG/SWCNT) was synthesized. Cyclic voltammetry was used to assess the ORR characteristics of Pt-NG/SWCNT catalytic layers. Only at a density of SWCNT to solvent ratio of 0.75 mg ml−1 were the ORR peaks clearly visible. Because of the high resistivity of SWCNT layers, the ORR peaks in other ranges, 0.4 mg ml−1 to 2.0 mg ml−1, were not clearly observed. The effect of SWCNT concentration on conductivity was proven to follow the basic concept of the percolation threshold.

DOI： 10.1002/fuce.202200020

Low-potential and high-capacity lithium battery anode based on hierarchical assemblies of Na<inf>2</inf>TiSiO<inf>5</inf> nanotubes Reviewed International coauthorship

Zhang Y., Huang J., Saito N., Zhang Z., Yang L., Hirano S.i.

Applied Surface Science Vol. 604 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Surface Science

Titanium-based materials such as TiO2 and Li4Ti5O12 are promising candidates for next-generation lithium-ion batteries (LIBs), but the high operating potential and unsatisfactory specific capacity severely restrict the potential application prospects. Li2TiSiO5 as a novel anode has attracted great attention due to its low-potential and high-capacity properties, but the conversion transition of Li2TiSiO5 to Li4SiO4 and TiO during Li+ intercalation and de-intercalation unfavorably affects the structural stability and hinders Li+ transport. Herein, novel cocoon-like microspheres assembled by Na2TiSiO5 nanotubes (NTSO-T), as the substitute of Li2TiSiO5, are facilely synthesized through a hydrothermal reaction. The hierarchical structure could effectively facilitate the Li+ diffusion, reduces internal strain, and enhances structural stability without greatly reducing the tap density. With a low but safe operating potential of 0.75 V, NTSO-T anode exhibits a high reversible capacity of 400 mAh g−1 which exceeds most reported Ti-based anodes, and durable long-cycling performance (capacity retention after 3000 cycles reaches 77%). Most importantly, the rate capability of NTSO-T is significantly enhanced. Kinetic reaction analysis has demonstrated the pseudocapacitive contribution in NTSO-T anode dominates the lithium storage kinetics. In addition, ex situ XRD and Raman analysis reveal a partially reversible conversion mechanism occurring in the framework. The excellent electrochemical performance of NTSO-T provides a promising anode candidate for next-generation LIBs.

DOI： 10.1016/j.apsusc.2022.154409

Multi-strategy synergistic in-situ constructed gel electrolyte-binder system for high-performance lithium-ion batteries with Si-based anode Reviewed International coauthorship

Zhao E., Luo S., Zhang Z., Saito N., Yang L., Hirano S.i.

Electrochimica Acta Vol. 434 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta

Silicon-based material have been considered as the most competitive candidate for next-generation anode in lithium-ion batteries (LIBs) due to its high specific energy density, natural abundance and attractive operating voltage. However, silicon-based anodes generally undergo significant volume changes and structural collapse during cycling, resulting in limited battery lifespan. Herein, a multi-strategy optimized in-situ gel electrolyte-binder system (GEBS) is rationally constructed, and electrochemical performances of the LIBs with Silicon-Graphite (Si-Gr) anodes are systematically evaluated by half-cell and full-cells. The in-situ generated polymer skeleton and improved interfacial compatibility of the GEBS effectively preserve the electrode structural integrity. Compared with the commercial liquid electrolyte, the volume change of the anode cycled with GEBS is suppressed from 208 % to 126 %. Benefiting from these merits, the full-cell with LiFePO4 cathode displays stable cycling stability with the capacity retention of 96.8 % after 260 cycles. Besides, the reversible capacity of the LiNi0.6Co0.2Mn0.2O2║Si-Gr full-cell is as high as 121.7 mAh g−1 after 200 cycles (capacity retention of 85.1 %), and the GEBS also exhibits obvious dominance at 55°C. This contribution effectively integrates multiple optimization strategies for Si-based anode and provides a feasible solution to address the challenge of its practical application in LIBs.

DOI： 10.1016/j.electacta.2022.141299

Remediation of water contaminated with polycyclic aromatic hydrocarbons using liquid phase plasma: Influence of electrical discharge condition

Kim U.J., Saito N., Lee S.H.

Frontiers in Marine Science Vol. 9 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers in Marine Science

Although the number of vessels with exhaust gas cleaning systems (EGCSs or scrubbers) has sharply increased to comply with strengthened regulations for marine environment, secondary pollutions are caused by discharged polycyclic aromatic hydrocarbons (PAHs) from scrubber effluent. Here, liquid-phase plasma (LPP) is employed to remediate water contaminated with PAHs. The increased frequency and pulse width enhanced the degradation efficiency, and 93.3, 90.7, 86.0, and 85.4% for naphthalene (Nap), acenaphthene (Ace), fluorene (Flu), and phenanthrene (Phe), respectively, are degraded at a frequency of 30 kHz and pulse width of 3 μs in 10 min. Considering physical condition of the plasma, long pulse width accelerated electrons, leading to increased generation of active species from intensified collision between electrons and surrounding molecules. Conversely, high frequency decelerated electrons due to the excessive changes in the polarity. However, the increased number of plasma discharges results in the generation of numerous active species. Generations of •OH and O radicals are confirmed by optical emission spectrometry and electron paramagnetic resonance. In addition, changes in functional groups which are corresponding to hydroxyl and oxygen groups are identified by Fourier transform infrared spectroscopy. Total PAHs in real scrubber are reduced from 1.1 to 0.4 μgL-1 with degradation efficiency of 63.6% after 10 min of LPP treatment. This study suggests LPP can be a promising method to protect diverse aqueous environments and provides optimal electrical discharge condition for degradation of organic pollutants.

DOI： 10.3389/fmars.2022.1033962

Hierarchical Porous Carbon Fibers Synthesized by Solution-Plasma-Generated Soot Deposition and Their CO<inf>2</inf> Adsorption Capacity

Romero Valenzuela A.E., Chokradjaroen C., Thiangtham S., Saito N.

Coatings Vol. 12 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings

Global warming caused by CO2 emissions is a major environmental problem. Thus, the development of materials with innovative architectures that approach the CO2 problem is a necessity. In this study, hierarchical porous carbon fibers (HCFs) were synthesized by a chemical deposition process that operates at 400 °C and uses solution-plasma-generated soot (PGS) as a carbon precursor. Subsequently, the CO2 adsorption capacity of the synthesized material was evaluated. The HCFs showed enhanced surface areas and networks of micropores and mesopores. Moreover, the HCFs were post treated by metal etching and KOH activation. The post treated HCFs achieved a CO2 uptake of 0.8 mmol g−1 at 273 K, which was superior to the simultaneously produced solution plasma carbon (SPC), which has a CO2 uptake of 0.2 mmol g−1.

DOI： 10.3390/coatings12111620

Plasma–Solution Junction for the Formation of Carbon Material

Niu J., Chokradjaroen C., Sawada Y., Wang X., Saito N.

Coatings Vol. 12 ( 11 ) 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs to be urgently explored to achieve the modulation of the SPP. Here, to address the knowledge gap, we experimentally determined the physical parameters of the spital distribution in the plasma phase, plasma–gas phase, and gas–liquid phase of the SPP by the Langmuir probe system with modification. Based on the assumption that plasma can act similarly to semiconductors with the Fermi level above the vacuum level, an energy band diagram of the plasma–solution junction could be proposed for the first time. It was observed that the Fermi level of the organic molecule could determine the magnitude of electron temperature in plasma, i.e., benzene produced the highest electron temperature, followed by phenol, toluene, and aniline. Finally, we found that the electron temperature at the interface could induce quenching, leading to the formation of multilayer large-size-domain carbon products. It provided significant evidence for achieving nonequilibrium plasma modulation of carbon nanomaterial synthesis.

DOI： 10.3390/coatings12111607

Layered Perovskite Lithium Yttrium Titanate as a Low-Potential and Ultrahigh-Rate Anode for Lithium-Ion Batteries

Zhang Y., Huang J., Saito N., Yang X., Zhang Z., Yang L., Hirano S.i.

Advanced Energy Materials Vol. 12 ( 31 ) 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Energy Materials

Graphite, as the dominant anode for commercial lithium-ion batteries, features sluggish electrochemical kinetics and low potential close to lithium deposition, leading to poor rate capability and safety issues. Although titanium-based oxides have received considerable attention, each alternative demonstrates unsatisfactory trade-offs between capacity, operating potential, rate capability, and lifespan. Here, submicrometer-sized lithium yttrium titanate (LYTO) is synthesized through facile sol–gel and ion-exchange reactions. With an average operating potential of 0.3 V versus Li+/Li, the LYTO anode demonstrates a high specific capacity of 236 mAh g–1 and durable cycling performance of 98% capacity retention after 3000 cycles. Impressively, without additional modification, a high-rate capability is achieved under a current density range from 0.5 C to 100 C (1 C = 200 mA g–1), e.g., delivering 112 and 87 mAh g–1 at 60 C and 100 C, respectively. Comprehensive characterizations and computational simulations reveal reversible solid-solution reactions occurring in the LYTO framework with little lattice change and fast 2D Li+ mobility achieved due to a low diffusion energy barrier. After incorporation with a LiFePO4 cathode, the energy density of the as-fabricated full cell reaches 2.4 times that of Li4Ti5O12/LiFePO4 full cell. The double characteristics of LYTO provide a fresh identification for high-performance anodes.

DOI： 10.1002/aenm.202200922

A non-flammable, flexible and UV-cured gel polymer electrolyte with crosslinked polymer network for dendrite-suppressing lithium metal batteries

Gu Y., Yang L., Luo S., Zhao E., Saito N.

Ionics Vol. 28 ( 8 ) page： 3743 - 3759 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Ionics

A flexible, non-flammable gel polymer electrolyte (GPE) was synthesized by combining UV-cured polymerization of ethoxylated trimethylolpropane triacrylate (ETPTA) within the framework of glass fiber (GF) membrane. Non-flammable hydrofluoroether (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, FEPE) and high flash point solvent (fluoroethylene carbonate, FEC) were employed as plasticizers for GPE-FEC/FEPE (60:40) to promote the safety of electrolyte and improve the compatibility with lithium metal anode. Non-flammable GPE-FEC/FEPE (60:40) possessed high safety level, high ionic conductivity (1.57 mS cm−1 at 30 °C), excellent oxidation stability (4.6 V vs. Li/Li+), high lithium-ion transference number (0.71) and good thermal stability (120 °C). After 1000 h test, Li/GPE-FEC/FEPE (60:40)/Li displayed better compatibility with lithium metal electrode compared with commercial liquid electrolyte. The test of Li/LFP cells showed that the safe GPE-FEC/FEPE (60:40) had excellent cycling performance at room temperature and elevated temperature. After 1000 cycles at 2 C and room temperature, the capacity retention was as high as 88.4%. XPS spectra proved that GPE-FEC/FEPE (60:40) was beneficial to promote the formation of LiF-rich SEI film on the surface of lithium metal anode, which could effectively inhibit the growth of lithium dendrites.

DOI： 10.1007/s11581-022-04621-4

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