Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Corrigendum to “Solid-state rigid polymer composite electrolytes with in-situ formed nano-crystalline lithium ion pathways for lithium-metal batteries” [Energy Storage Materials Volume 72 (2024) 103714] (Energy Storage Materials (2024) 72, (S2405829724005403), (10.1016/j.ensm.2024.103714)) Reviewed Open Access

Wei Z., Huang J., Liao Z., Hu A., Zhang Z., Orita A., Saito N., Yang L.

Energy Storage Materials Vol. 77 2025.4

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

The authors regret. In the second paragraph in the introduction, we delete "The PBDT not only breaks the trade-off between ionic conductivity and modulus, but also provides a controlled macroscopic arrangement in the formed ionic gels." and here add "Wang et al [1] significantly enhanced the lithium ion conductivity by introducing a grain boundary network filled with LiFSI and LiBF<inf>4</inf> nanocrystals into PBDT-gels. This polymer composite electrolyte exhibits not only good ionic conductivity but also high lithium ion transference number and mechanical modulus. Based on the excellent performance of such polymer electrolytes, a similar concept was designed and constructed in the PBDT matrix in our work, aiming to apply it in lithium metal secondary batteries." The authors would like to apologise for any inconvenience caused.

DOI： 10.1016/j.ensm.2025.104102

Solution plasma synthesis of nitrogen-doped carbon dots from glucosamines: Comparative fluorescence modulation for dopamine detection Reviewed International coauthorship International journal

Treepet S., Duangmanee T., Chokradjaroen C., Kim K., Saito N., Watthanaphanit A.

Carbon Vol. 231 2025.1

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

The intriguing fluorescence characteristics of carbon dots (CDs) have led to many sensor applications, particularly for dopamine (DA), a molecule linked to various diseases. This study prepares CDs from glucose and glucosamine (nitrogen-free and nitrogen-containing precursors) using a simple solution plasma process (SPP). We explore how nitrogen elements and counterions in glucosamine (hydrochloride and sulfate) affect CD properties and their ability to modulate fluorescence for DA detection. Glucosamine offers three advantages over glucose: (i) single-step CD synthesis via SPP, (ii) enhanced fluorescence of CDs, and (iii) improved fluorescence response to DA. We investigate the DA detection capabilities of N,S-CDs (from glucosamine sulfate) and N,Cl-CDs (from glucosamine hydrochloride). Both can sense DA with distinct photoluminescence responses. N,S-CDs show selectivity and fluorescence brightening upon DA interaction, with a detection limit of 33.05 μM. N,Cl-CDs demonstrate higher sensitivity with a lower detection limit of 0.1212 μM through fluorescence quenching. Silver ions (Ag<sup>+</sup>) may also contribute to N,Cl-CDs quenching; however, the observed color change to gray due to silver nanoparticle (AgNP) formation helps pinpoint the quenching substance. The varied photoluminescence responses arise from different surface functional groups: N,S-CDs have amino-rich surfaces, while N,Cl-CDs have conjugated carbonyl-rich surfaces. This study illustrates the mechanisms of DA detection and AgNP formation, suggesting the potential of CDs in medical diagnostics as selective tools for disease diagnosis. Additionally, we compare the DA sensing methodology of our CDs with existing literature, highlighting the advantages of our sensor.

DOI： 10.1016/j.carbon.2024.119705

Two-Dimensional Crystal Growth of MoS2 Thin Films from Sodium Dodecyl Sulfate Micellar Solutions and Wettability Between Solution and Substrate Reviewed Open Access

Zhu Z., Liu Y., Sawada Y., Saito N.

Coatings Vol. 15 ( 1 ) 2025.1

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

In this study, the growth of 2D MoS<inf>2</inf> thin films on SiO<inf>2</inf>/Si substrates was investigated using sodium dodecyl sulfate (SDS) micellar solutions, and the effects of SDS concentration and substrate treatment on crystal growth were evaluated. By increasing the SDS concentration, the wettability was improved, and uniform MoS<inf>2</inf> crystal growth was promoted by micellar formation. When the SDS concentration exceeded 10<sup>−4</sup> mol/L, the static contact angle sharply decreased, indicating uniform 2D material growth. The optimal conditions that enabled a uniform supply of Mo-based precursors were as follows: SDS concentration of 3.5 × 10<sup>−4</sup> mol/L; Na<inf>2</inf>MoO<inf>4</inf>·2H<inf>2</inf>O concentration of 1.7 × 10<sup>−2</sup> mol/L. The results indicate that solution-based processes using SDS are effective for 2D material growth, and they may be a valuable technique in future thin film device fabrication processes.

DOI： 10.3390/coatings15010004

Recent progress in fructose conversion to 2,5-furandicarboxylic acid using metal organic framework–derived catalysts Reviewed International coauthorship

Ibrahim I., Thiensuwan N., Rashid U., Chokradjaroen C., Saito N., Ngamcharussrivichai C.

Catalysis Reviews Science and Engineering 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：Catalysis Reviews Science and Engineering

Metal-organic frameworks (MOF) serve as versatile platforms for the development of multifunctional heterogeneous catalysts, enabling synergistic and tandem reactions owing to their diverse compositions, tunable pore sizes, and high porosities. MOF can accommodate multiple catalytic centers, either during synthesis or via post-synthetic modification, employing open metal sites, functionalized linkers, or encapsulated guest species as active sites. The integration of open metal sites with additional functional groups, particularly Brønsted acid sites, enhances the synergistic catalytic performance of MOF. The direct conversion of fructose to 2,5-furandicarboxylic acid (FDCA) is an attractive alternative to 5-hydroxymethylfurfural (HMF) as a substrate, given HMF’s high cost, instability, and complexity of the separation and purification steps. The demand for catalysts with multifunctional active sites arises from the sequential steps involved in this transformation, which include the Brønsted acid-catalyzed dehydration of fructose to HMF followed by oxidation of HMF to FDCA. This review highlights recent progress in the use of MOF-based catalysts not only for the conventional two-step process of fructose dehydration followed by HMF oxidation, but also for the one-pot conversion of fructose directly into FDCA. Furthermore, the current challenges associated with the development of a sustainable and industrially viable process for direct fructose-to-FDCA conversion are discussed.

DOI： 10.1080/01614940.2025.2573297

Microenvironment Regulation via Synergistic Chain Topology and Weakly Coordinating Chemistry for Ultra-Stable High-Voltage Lithium Metal Batteries Reviewed

Hu A., Yang Q., Sun Y., Yang Z., Chen K., Huang J., Wei Z., Saito N., Zhang Y., Zhang Z., Chen L., Yang L.

Advanced Functional Materials 2025

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

In situ polymerized polyether electrolytes offer superior interfacial contact in lithium metal batteries (LMBs) but suffer from insufficient oxidative stability and uncontrollable interfacial reactions at high voltages. Herein, these limitations are addressed through microenvironment regulation, synergistically integrating chain topology control and weakly coordinating chemistry. A novel poly(ester-alt-ether) copolymer electrolyte (PMDGE) is synthesized through in situ copolymerization of 4-methyl-1, 3-dioxane and glutaric anhydride. The extended methyl-branched alkyl chains and weakly coordinating ester groups intrinsically lower the highest occupied molecular orbital (HOMO) energy of the polymer and weaken Li<sup>+</sup>-polymer interactions, significantly promoting anion participation in the Li<sup>+</sup> solvation sheath. Crucially, this molecular engineering drives the formation of dual inorganic-rich interphases: a LiF/Li<inf>x</inf>BO<inf>y</inf>F<inf>z</inf>-enriched solid electrolyte interphase effectively suppresses dendrites, while a LiF-dominant cathode electrolyte interphase mitigates oxidative decomposition. Consequently, PMDGE exhibits an expanded electrochemical window (5.2 V), a high lithium-ion transference number (0.58), and enables ultra-stable Li plating/stripping (>1200 h). Remarkably, Li|PMDGE|LiFePO<inf>4</inf> cell demonstrates unprecedented cycling stability, retaining 96.3% capacity after 10000 cycles at 2 C. Furthermore, Li|PMDGE|LiCoO<inf>2</inf> cell maintains 80.2% capacity after 1200 cycles at a cut-off voltage of 4.45 V. This work demonstrates molecular solvation engineering through polymer structure design as a powerful paradigm for designing high-performance polymer electrolytes in high-voltage LMBs.

DOI： 10.1002/adfm.202520686

Enhanced energy storage efficiency of an innovative three-dimensional nickel cobalt metal organic framework nanocubes with molybdenum disulphide electrode material as a battery-like supercapacitor Reviewed International coauthorship International journal

Palanisamy R., Pavadai N., Pavadai R., Saito N., Pattananuwat P., Sujaridworakun P.

Journal of Alloys and Compounds Vol. 1009 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Recently, metal-organic frameworks (MOFs) with transition metal sulfides have gained much attention as electrode materials for supercapacitors (SCs). In this work, 3D-NCMOF@MS NCs, incorporating two-dimensional molybdenum disulphide (2D-MS) nanosheets and three-dimensional nickel cobalt-MOF nanocubes (3D-NCMOF NCs) are synthesized by a solvothermal and precipitation process. Owing to their enhanced electrical conductivity and huge surface area, the 3D-NCMOF@MS NCs produce superior electrochemical responses in SCs compared to 2D-MS and 3D-NCMOF NCs. The results demonstrate that the synergistic 3D-NCMOF@MS NCs increased specific capacitance up to 1048 Fg<sup>−1</sup> at 1 Ag<sup>−1</sup>, revealing outstanding cycle stability with a capacitance retention of 99.06 %. Besides, the exposed high-power density of 3D-NCMOF@MS NCs reached 400 W kg<sup>−1</sup> as well as an outstanding maximum energy density of 188.64 Wh kg<sup>−1</sup>. Such synergistic effects of the multivalent states of Ni, Co, and Mo promote electrochemical characteristics, implying that the 3D-NCMOF@MS NCs could potentially be used in energy storage systems, boosting electrochemical performance.

DOI： 10.1016/j.jallcom.2024.176991

Platinum nanoparticles wrapped in carbon-dot-films as oxygen reduction reaction catalysts prepared by solution plasma sputtering International journal Open Access

Liu Y., Zhu Z., Wang P., Deng Z., Niu J., Sawada Y., Saito N.

Nanoscale Advances Vol. 7 ( 4 ) page： 1048 - 1060 2024.12

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

Fuel cells have become increasingly important in recent years because of their high energy efficiency and low environmental impact. However, key challenges remain in the widespread adoption of fuel-cell vehicles, including reducing Pt usage in catalysts and improving their durability. In this study, a high-performance Pt@carbon-dot-film core–shell catalyst was successfully synthesized using a nonequilibrium reaction field, i.e., solution plasma (SP) process, by adjusting the electrolyte pH. Four pH solutions (pH = 4.4, 7, 8, and 11) were employed as the discharge liquid environment for the SP process. The catalyst synthesized in the pH = 8 solution exhibited a mass activity of approximately 500 mA mg<sup>−1</sup>, which was twice as high as that of the commercial Pt/C catalyst (256 mA mg<sup>−1</sup>) with the same loading amount. The onset and half-wave potentials were 0.99 and 0.89 V, respectively, both of which exceeded those of commercial Pt/C catalysts (0.95 and 0.86 V, respectively). Furthermore, the enhanced catalytic performance corresponded to the Pt/C bonding between Pt and the carbon shell generated during the SP process.

DOI： 10.1039/d4na00818a

A Bandgap-Tuned Tetragonal Perovskite as Zero-Strain Anode for Potassium-Ion Batteries International coauthorship International journal Open Access

Yang W., Huang J., Zheng Q., Chen L., Orita A., Saito N., Zhang Z., Zhang Y., Yang L.

Angewandte Chemie International Edition Vol. 63 ( 52 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Angewandte Chemie International Edition

PIBs are emerging as a promising energy storage system due to high abundance of potassium resources and theoretical energy density, however, progress of PIBs is severely hindered by structural instability and poor cycling of anode material during continual insertion and extraction of larger-sized K<sup>+</sup>. Hence, developing anode material with structural stability and stable cycling remains a great challenge. Herein, band gap-tuned Mo-doped and carbon-coated lead titanate (CMPTO) with zero-strain K<sup>+</sup> storage is presented as ultra-stable PIBs anode. Mo doping introduces narrowed band gap and optimized crystal lattice for enhanced intrinsic electron and ion transfer. Demonstrated by in situ XRD characterizations, the crystal structure stays stable with unchanged peak positions, fully revealing zero-strain characteristic of CMPTO anode during potassium storage for stable cyclic capability. Ultimately, CMPTO anode achieved ultra-stable cycling performance of 7000 cycles at 500 mA g<sup>−1</sup> with high capacity retention of 90 % and considerable specific capacity of 130.9 mAh g<sup>−1</sup> after 600 cycles at 100 mA g<sup>−1</sup>; with relatively large density, CMPTO realized eminent volumetric capacity of 1111.09 mAh cm<sup>−3</sup> and ultra-long cycling life of 10000 cycles at 7041 mA cm<sup>−3</sup>. This work introduces a promisingly new route into developing anode materials with ultra-stable performance for PIBs.

DOI： 10.1002/anie.202412706

Interphase Optimum via Synergistic Effect of Poly(1,3-dioxolane) Electrolytes and Lithium Difluorophosphate for Stable Lithium Metal Batteries International coauthorship International journal

Hu A., Liao Z., Yang Q., Huang J., Wei Z., Sun Y., Zhao E., Zhang Z., Yang L., Saito N., Orita A.

Advanced Functional Materials Vol. 34 ( 51 ) 2024.12

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

Solid polymer electrolytes (SPEs) hold great promise for future applications of high-energy lithium metal batteries (LMBs). Unfortunately, inadequate room-temperature ionic conductivity, sluggish interfacial charge transport, and uncontrolled electrode/electrolyte interface reactions severely limit their widespread applications. Herein, poly(1,3-dioxolane) electrolytes (PDEs) are prepared in situ by introducing lithium difluorophosphate (LiDFP, LiPO<inf>2</inf>F<inf>2</inf>) as a multifunctional additive, which not only achieves excellent ionic conductivity but facilitates interfacial charge transport. Meanwhile, a high-mechanical-stability organic–inorganic hybrid solid electrolyte interphase (SEI) is formed by the synergistic effect of PDEs and LiDFP. The enrichment of LiF and Li<inf>x</inf>PO<inf>y</inf>F<inf>z</inf> species in SEI formed by the preferential reduction of LiDFP ensures outstanding mechanical stability, and the ring-opening polymerization of 1,3-dioxolane provides the SEI excellent adaptability to the repetitive volume changes of lithium metal anode, which mitigates crack and regeneration of SEI and reduces side reactions between active Li and electrolytes. Therefore, based on PDEs, the symmetric Li cell enables steady cycling for 2000 h. The Li-LiFePO<inf>4</inf> cell achieves superior long-term cycling stability (over 1200 cycles) and wide operating temperature (−20 ∼ 60 °C). Also, the Li-LiNi<inf>0.6</inf>Mn<inf>0.2</inf>Co<inf>0.2</inf>O<inf>2</inf> exhibits favorable cycling stability. This study provides solutions to ongoing pain point issues of SPEs and facilitates practical applications of SPEs in high-energy LMBs.

DOI： 10.1002/adfm.202410282

Few-Layer MoS2 on a SiO2/Si Wafer through Sulfurization Chemical Vapor Deposition with a Vaporization-Shadowing Effect International journal

Zhu Z., Liu Y., Sato K., Niu J., Chokradjaroen C., Sawada Y., Saito N.

ACS Applied Nano Materials Vol. 7 ( 17 ) page： 20257 - 20266 2024.9

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

This study aimed to synthesize few-layer MoS<inf>2</inf> on SiO<inf>2</inf>/Si using sulfurization chemical vapor deposition toward beyond-5G and 6G communication. Fabric-like MoO<inf>3</inf>(s) was directly placed onto a SiO<inf>2</inf>/Si substrate to lower the oxygen potential, which is achieved through a shadowing effect on vaporization. Successful results were achieved, yielding MoS<inf>2</inf> thin films with a coverage of more than 74% and a crystal size in the range of 50 to 600 μm. Two distinct pathways for MoS<inf>2</inf>(s) formation from MoO<inf>3</inf>(s) via MoO<inf>2</inf>(s) and MoS<inf>3</inf>(s) were also uncovered. The shadowing effect of MoO<inf>3</inf>(s) vaporization facilitated the two-dimensional growth of MoS<inf>2</inf> by mitigating oxygen partial pressure. Therefore, sulfurization chemical vapor deposition shows great application potential in synthesizing high-quality MoS<inf>2</inf> thin films with substantial crystal size and coverage, making them suitable for next-generation communication devices.

DOI： 10.1021/acsanm.4c03188

Surface functionalization of cellulose derived from hemp by tetraethyl orthosilicate (TEOS) and poly vinylidene fluoride (PVDF)-based composite separator membrane for lithium-ion batteries (LIBs) International coauthorship International journal Open Access

Sirichaibhinyo T., Thiangtham S., Saito N., Ummartyotin S.

Results in Engineering Vol. 23 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Results in Engineering

Separators play a crucial role in enhancing the electrochemical performance of lithium-ion batteries (LIBs). However, achieving separators with exceptional electrochemical performance and high stability remains a significant challenge. In this study, we meticulously designed composite membranes based on polyvinylidene fluoride (PVDF) with varying contents of microcrystalline cellulose/tetraethyl orthosilicate (MCC/TEOS). The increase in hydrophilicity of PVDF by adding MCC-TEOS weight contents endowed the 3 wt% MCC/TEOS-based PVDF separator membrane with superior electrolyte absorption and reduced resistance, resulting in an impressive ionic conductivity of 0.514 mS/cm higher than the pristine PVDF membrane (0.253 mS/cm). Furthermore, the LIB cell utilizing the 3 wt % MCC/TEOS-based PVDF separator membrane consistently demonstrated stable charge/discharge profiles at a rate of 0.2C, achieving a specific capacity of 98 mAh/g, compared to only 43 mAh/g for the pristine PVDF membrane. These findings underscore the significant potential of MCC/TEOS as a biofiller for bio-membranes, making it an optimal choice for applications in LIBs.

DOI： 10.1016/j.rineng.2024.102807

Solid-state rigid polymer composite electrolytes with in-situ formed nano-crystalline lithium ion pathways for lithium-metal batteries International coauthorship International journal

Wei Z., Huang J., Liao Z., Hu A., Zhang Z., Orita A., Saito N., Yang L.

Energy Storage Materials Vol. 72 2024.9

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

Polymer-based solid-state electrolytes with excellent processability and flexibility are ideal candidates for commercialisation in lithium-metal batteries. However, the current polymer-based solid-state electrolytes still have many problems such as low ionic conductivity, limited Li<sup>+</sup> transport number and high interfacial resistance with electrodes. To address the above challenges, a solid-state rigid polymer composite electrolyte with high ionic conductivity (2.8 mS cm<sup>−1</sup>) has been prepared based on the rigid polymer poly(2, 2′-disulfonyl-4, 4′-benzidine terephthalamide) (PBDT). Locally aligned PBDT-EMImN(CN)<inf>2</inf> grains are interspersed with in-situ formed interconnected LiFSI to form the structure of the polymer composite electrolyte. The formation of defective LiFSI nanocrystals at grain boundaries inside the polymer electrolyte acts as additional conductive networks providing fast Li<sup>+</sup> transportation (t<inf>Li</inf><sup>+</sup> = 0.59). The flexible region in the electrolyte gives excellent interfacial impedance (32.5 Ω cm<sup>2</sup>) with Li-metal electrode. The Li||Li batteries can be stably cycled for over 1000 cycles at 1 mA cm<sup>−2</sup> (25 °C). The assembled Li||LiFePO<inf>4</inf> batteries exhibit excellent cycling and multiplication performance over a wide operating temperature (from −20 to 60 °C). Moreover, this electrolyte material exhibits compatibility with high-voltage cathode LiNi<inf>0.6</inf>Mn<inf>0.2</inf>Co<inf>0.2</inf>O<inf>2</inf> batteries. This electrolyte and design strategy is expected to inspire the realization of all-weather practical solid-state lithium-metal batteries.

DOI： 10.1016/j.ensm.2024.103714

Improving the durability and anti-poisoning properties of platinum catalysts by carbon shell encapsulation: A promising approach for both cathode and anode catalysts for polymer electrolyte membrane fuel cells

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

International Journal of Hydrogen Energy Vol. 72 page： 642 - 651 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy

Carbon shell encapsulation has emerged as an effective strategy for enhancing the durability of Pt-based electrocatalysts for polymer electrolyte membrane fuel cells (PEFCs). Here, a nitrogen-doped carbon shell-encapsulated Pt catalyst supported on Ketjen black (Pt@C/KB) was synthesized, and its catalytic performance was characterized. The oxygen reduction reaction (ORR) performance and anti-poisoning properties were investigated in 0.1 M HClO<inf>4</inf> with and without H<inf>2</inf>SO<inf>4</inf> or H<inf>3</inf>PO<inf>4</inf> poisoning, using a rotating ring-disk electrode (RRDE) technique. Despite a decrease in the electrochemical surface area (ECSA), Pt@C/KB encapsulated by a thin graphene-like carbon shell (<1 nm thick) showed high selectivity for the four-electron reaction due to its superior anti-poisoning properties, as well as improved ORR activity and durability. The H<inf>2</inf>O<inf>2</inf> yield of Pt@C/KB, the precursor of hydroxyl radicals, was decreased approximately one third compared to bare Pt catalyst and the gap was more pronounced in the low potential (E ≤ 0.1 V/RHE) where close to practical anode potential, suggesting that Pt@C/KB can be applied as a new anode catalyst. Applying carbon core-shell catalysts to both the cathode and anode is a prospectively effective approach for improving the cell performance by improving the ORR activity and anti-poisoning properties, as well as for extending the lifespan of PEFCs.

DOI： 10.1016/j.ijhydene.2024.05.394

Nitrogen-Doped Carbon Nanothin Film as a Buffer Layer between Anodic Graphite and Solid Electrolyte Interphase for Lithium-Ion Batteries International coauthorship International journal Open Access

Ukai J., Kim K., Matsuhara S., Yang L., Saito N.

ACS Omega Vol. 9 ( 23 ) page： 24372 - 24378 2024.6

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

Lithium-ion batteries are essential batteries for electric vehicle drive systems. Such batteries must provide stable performance over a long period of time. Therefore, the degradation or aging of the battery capacity must be improved. In the case of the current graphite anodes, graphite coated with an amorphous layer is used. It is known that the amorphous layer can reduce the irreversible capacity loss caused by the solid electrolyte interphase (SEI) layer. The amorphous carbon layers reduce the initial capacity due to higher electrical resistance. In this study, we aim to develop a buffer layer using nitrogen-containing graphene that would prevent the increase in electrical resistance while maintaining the amorphous structure. Coatings with different film thicknesses were prepared by using the solution plasma method. The thinnest sample was oven sintered to optimize the structure, especially the surface and interface of the layer. The battery capacity from charge-discharge experiments and the resistance change of each part from electrochemical impedance measurements were evaluated. The results showed that the coating layer increased the electrical resistance of the graphite anode. On the other hand, the resistance of the SEI layer was reduced by the coating layer. It can be predicted that the addition of the coating layer will increase the total charge transfer resistance (R<inf>ct</inf>) of the cell but will also improve the period average capacity in the long run. To be used as a practical material, the film thickness would need to be further reduced, and the balance between the loss of charge transfer resistance and the gain of SEI layer resistance would need to be further optimized.

DOI： 10.1021/acsomega.3c10502

First-principles studies of enhanced oxygen reduction reactions on graphene- and nitrogen-doped graphene-coated platinum surfaces

Nam H.N., Phung Q.M., Choeichom P., Yamauchi Y., Saito N.

Physical Chemistry Chemical Physics Vol. 26 ( 14 ) page： 10711 - 10722 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Developing innovative platinum-based electrocatalysts and enhancing their efficiency are crucial for advancing high-performance fuel cell technology. In this study, we employed DFT calculations to provide a theoretical basis for interpreting the impact of graphene coatings on various Pt surfaces on oxygen reduction reaction (ORR) catalytic activity, which are currently applied as protective layers in experiments. We comprehensively assess the geometric and electronic properties of Pt(100), Pt(110), and Pt(111) surfaces in comparison to their graphene-coated counterparts, revealing different adsorption behaviors of O<inf>2</inf> across these surfaces. The ORR mechanisms on different Pt surfaces show distinct rate-determining steps, with Pt(111) showing the highest ORR activity, followed by Pt(110) and Pt(100). Graphene coatings play a key role in enhancing charge transfer from the surface, resulting in modifications of O<inf>2</inf> adsorption. Despite influencing ORR kinetics, these graphene-coated surfaces demonstrate competitive catalytic activity compared to their bare counterparts. Notably, Pt(111) with a graphene coating exhibits the lowest activation energy among graphene-coated surfaces. Our calculations also suggest that the ORR can occur directly on non-defective Pt@graphene surfaces rather than being restricted to exposed Pt centers due to point defects on graphene. Furthermore, our work highlights the potential of nitrogen doping onto the Pt(111)@C surface to further enhance ORR activity. This finding positions nitrogen-doped Pt@C as a promising electrocatalyst for advancing electrochemical technologies.

DOI： 10.1039/d4cp00269e

Nanoarchitectonics Solution Plasma Polymerization of Amino-Rich Carbon Nanosorbents for Use in Enhanced Fluoride Removal International coauthorship

Tipplook M., Tanaka H., Sudare T., Hagio T., Saito N., Teshima K.

ACS Applied Materials and Interfaces Vol. 16 ( 6 ) page： 7038 - 7046 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Amino-functionalized carbon (NH<inf>2</inf>C) is an effective adsorbent in removing pollutants from contaminated water because of its high specific surface area and electrical charge. In the conventional preparation method, the introduction of amino groups onto the carbon surface is limited, resulting in low pollutant adsorption. Herein, we present simultaneous carbonization and amination to form NH<inf>2</inf>C via electrical discharge of nonequilibrium plasma, and the resultant material is applied as an effective adsorbent in fluoride removal. The simultaneous process introduces numerous amino groups into the carbon framework, enhancing the adsorption efficiency. The fluoride adsorption capacity is approximately 121.12 mg g<sup>-1</sup>, which is several times higher than those reported in previous studies. Furthermore, computational modeling is performed to yield deeper mechanistic insights into the molecular-level adsorption behavior. These data are useful in designing and synthesizing advanced materials for applications in water remediation.

DOI： 10.1021/acsami.3c15172

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

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)<inf>2</inf>AlTi (L2<inf>1</inf>) 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/cm<sup>3</sup> (<6 g/cm<sup>3</sup>). 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 L2<inf>1</inf> phase, consisting of (Cu, Co)<inf>2</inf>AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L2<inf>1</inf> 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

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