ナノプロトニクス

In this study, we fabricated MOF thin films composed of Zn2+, tetrakis-(4-carboxyphenyl)-porphyrin (TCPP), and 4,4′-bipyridyl (bpy) at 10 and 40% relative humidity (RH) conditions. Then, we investigated the humidity effects on chemical compositions of TCPP and bpy, periodic structure, orientation, and surface morphology. At high RH, coordination replacement of water with the organic linkers becomes more competitive than that at low RH, resulting in a different TCPP/bpy composition ratio between the two RH conditions.

The author summarized recent diverse applications and advancements for proton-conducting polymers since 2018, emphasizing their importance in various technological areas. These polymers are integral to fuel cells, water electrolysis, energy storage systems, actuators, and sensors, offering high proton conductivity, chemical stability, and adaptability.

This concise review paper specifically described advancements in proton and hydroxide ion-conductive polymers, emphasizing their structural organization and molecular orientation by various intrinsic molecular interactions and external environmental conditions.

A strategy to tune the emission properties of COFs by introducing atoms or small molecular groups as surface perturbations.

The unique Christmas-tree-shaped Pd nanostructures were generated through a simple electrodeposition technique on the glassy carbon electrode (GCE). The modified electrode showed excellent catalytic activity than the unmodified GCE for ascorbic acid electro-oxidation in alkaline condition. This high efficiency is derived from the many hierarchical edges of nanostructures.

This study investigated the influence of carboxylic acid concentration on both interfacial and internal proton transport. Remarkably, polymer thin films with high carboxylic acid concentration provide internal proton conduction. In contrast, interfacial proton conduction was found in low carboxylic acid concentration polymers. This study provides insight into interfacial proton transport behavior according to the weak acid concentration, which might explain proton transport in biological systems.

The Cover Feature shows the conduction of OH− ions in poly[(9,9-bis(6′-(N,N,N-trimethylammonium)-hexyl)-9H-fluorene)-alt-(1,4-benzene)] (PFB+) anion-exchange thin film. The OH− conductivity of PFB+ thin film is comparable to the reported OH− conductivity of PFB+ bulk membrane. Both reduced OH− conductivity and water uptake can be observed in thinner PFB+ film.

Well-defined silver dendrite nanostructures with primary and secondary branches on a glassy carbon electrode (GCE) surface are first demonstrated using a simple wet chemical electroless deposition method without any aid of a surfactant.

Several current topics are introduced in this review, with particular attention to highly proton-conductive polymer thin films with organized structure and molecularly oriented structure.

Relative mobility and number of density of proton carriers were discussed in sulfonated polyimide thin films.

Influence of the semi-aliphatic backbone on the molecular ordering and proton conductivity was investigated compared to the rigid aromatic backbone in highly proton-conductive organized polyimide thin films. The higher molecular weight ASSPI exhibited the oriented lamellar structure in spite of lower planarity of the main chain. The proton conductivity of the oriented lamellar thin film displayed a more than half order of magnitude higher value of 1.5 × 10-1 S cm-1 than that of the non-oriented lamellar thin film (3.0 × 10-2 S cm-1) at 25°C and 95% RH. These results indicate that, in sulfonated polyimide thin films, the lamellar orientation greatly contributes to the high proton conductivity in the ASSPI thin films.

In-plane proton conductivity and interfacial structure of Nafion thin films on the Au-deposited surface and MgO(100) substrate were investigated.

高プロトン伝導性高分子には，エネルギー変換，センサー，触媒，アクチュエータなどさまざまな用途がある．含水により高プロトン伝導性を示す高分子の分子設計は，強酸性基を骨格に導入し，含水により親疎水の相分離構造を形成させ，親水チャネルを使ってプロトンを輸送させることに基づいている．Nafionのような高プロトン伝導性高分子は，相分離構造を示すものの，長距離秩序をもたないために，構造とプロトン伝導性の相関の議論は容易ではなかった．筆者らの研究グループは基板界面を利用して高分子を配向させ，分子配向がプロトン伝導性に与える影響を調べてきた．本報では，Nafionの薄膜化によるプロトン伝導度の低下，アミドオリゴマー薄膜のプロトン伝導度の基板依存性，ポリペプチド薄膜の分子配向によるプロトン伝導度の向上，およびスルホン化ポリイミド薄膜が有するリオトロピック液晶性による組織構造と高プロトン伝導性の相関を述べる．

Alkyl sulfonated polyimides (ASPIs) with bent main chain structure were newly synthesized to investigate relations between the higher order structure and proton transport properties. Proton conductivity of all polyimide thin films was greater than 10–2 S/cm. Grazing-incidence small-angle X-ray scattering (GI-SAXS) revealed that both planar and bent ASPI thin films exhibited humidity-induced lyotropic lamellar structure. Results demonstrate that sulfonated alkyl side chains contribute strongly to the lyotropic LC property, which enhances molecular orderings and proton conductivity by water uptake.

This is the first report about the synthesis of triblock copolymers containing catechol groups by reversible-addition fragmentation transfer (RAFT) polymerization. The synthesized triblock copolymer forms a core–shell cylinder (CSC) phase-separated structure, in which PVCa domains located the surface of cylinders, and it works as a template for silver nanoparticle arrays and a proton conductive channel.

Pd nanoparticles were electrochemically immobilized on Pt surface in presence of sodium dodecyl sulfate (SDS) molecules to study electrokinetics of arsenite oxidation reactions and corresponding sensing activities. The experimental results revealed the As(III) oxidation proceeds using a consecutive pathway; As(III) → As(IV) → As(V).

We demonstrated a solution-based molecular layer deposition (MLD) approach to prepare porphyrin-based covalent organic molecular networks on a modified substrate surface using the urea coupling reaction at room temperature.

This Feature Article presents a new approach to enhancing the proton conductivity of the polymer thin films using an interface that can modify the degrees of freedom for a polymer structure through interaction between the substrate surface and polymers.

A facile, efficient and rapid method for fabrication of silica-coated Fe2O3 magnetic nanoparticles (NPs) by a microwave (MW) irradiation method is reported.

Crystalline and amorpous parts are discussed in the sulfonated polyimide thin films to understand the proton transport property.

Size-controlled metal nanoparticles (NPs) were spontaneously formed. The proton conductivity of well-aligned lamellae structured PVCa-b-PSt films with Ag NPs was evaluated. We found that the proton conductivity of PVCab-PSt film was increased 10-fold by the addition of Ag NPs into the proton conduction channels filled with catechol moieties.

The growth of metal–organic coordination network thin films on surfaces has been pursued extensively and intensively to manipulate the molecular arrangement.

The preparation of urea (bonded) cross-linked multilayer thin films by sequential deposition of bifunctional and tetrafunctional molecular building blocks is demonstrated. Molecular ordering and mass density increase in the surface normal direction of the substrate with a certain number of deposited layers.

The effects of Cl− and SO42− ions on the electrocatalytic nitrate reduction activities in a sandwich-type reactor assembly are illustrated. It was noticed that a Pt|Nafion|Pt–Cu assembly offers its best efficiency in the absence of any supporting electrolytes.

Hydrophobized plant polyphenol can be easily prepared by rational and controlled etherification of highly abundant aromatic hydroxyls with linear alkyl chains. The resultant organo-soluble polyphenols spontaneously formed fibrous structures and unravelled to be potential adhesive, anticorrosion, and antibacterial coatings.

Understanding the Nafion-Pt interface structure is important because fuel cell reactions occur at the three-phase boundary. However, the interface structure of the Nafion-Pt interface remains unclear. In this study, relationship between the proton transport property and thin film structure on the Pt-deposited surface at the three-phase boundary for fuel cells is discussed. Thickness dependence of the degree of orientation for this OP band was observed at the Nafion-Pt interface.

An vapochromic luminescence enables visualization of the ion conductivity of the material by the color of the luminescence.

The effect of molecular ordering and ordered domain size on molecular weight dependent proton conductivity in well-organized sulfonated polyimide (SPI) thin films has been investigated.

We demonstrated the utilization of practical film-forming technique inkjet printing to fabricate a Nafion ultra-thin film less than 10nm thickness. Post-treatment in an ethanol vapor atmosphere exhibited a significant effect on flattening and homogenizing the film surface morphology. Results show that the well-distributed Nafion ultra-thin film modified by ethanol vapor annealing manifested much-improved proton conductivity.

Proton conductivity of crystallized water clusters confined within low-dimensional nanoporous materials

The organized structure and proton transport property in sulfonated polyimide (SPI) thin film have been studied. The high proton conductivity of 2.8 × 10−1 S cm−1 at 80°C and 90% RH was achieved in the highly oriented SPI thin film. In contrast, the bulk SPI showed the drop of conductivity value at high relative humidity region, which is due to the significant structural disorder accompanied by the strong interaction between the sulfonic acid side chains and water molecules.

Proton transport of fully protonated poly(aspartic acid) thin film was investigated. The thin film structure differed greatly from the partially protonated one. Proton transport occurs on the surface, not inside of the thin film. This result contributes to biological transport systems such as bacteriorhodopsin.

Studies of proton transport in confined thin polymer electrolytes are essential for providing additional information regarding the structure–property relationships of such materials. Sulfonated polyimide film confined to a thickness of approximately 530 nm shows significant proton conductivity enhancement to a value of 2.6 × 10−1 S/cm (95% RH at 298 K).

We present a method of using inkjet printing to deposit Nafion ionomer as the transport media onto catalyst layer made into membrane electrode assemblies (MEAs) for polymer electrolyte fuel cells (PEMFCs).

Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (P-Asp) were investigated. A remarkable enhancement of proton conductivity has been achieved in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4 × 10–3 S cm–1 at 298 K.

The molecular orientation in the thin film could be correlated with the proton-transport properties.

Nafion thin film on Si substrate had a highly oriented structure with the sulfonic acid groups at the side chain. The lower proton conductivity of the Nafion thin film was related with these highly oriented structures.

Contact angle measurements and an infrared p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) technique were performed on MgO(100) and quartz substrates.

The proton conductivity of two thin films were quite lower values compared to that of the commercial Nafion membrane, and the thickness dependence of the proton conductivity was also observed.

Protonconcutive photocurable electrolytes were prepared. Patterning of micro-structure on the photocured membrane was also demonstrated by using the property of the photocurable electrolytes.

Iridium oxide supported on Vulcan XC-72 carbon black (IrO2/C) as a cathode catalyst for polymer electrolyte fuel cell (PEFC) has been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV). It was found that IrO2/C had high oxygen reduction reaction (ORR) activity. IrO2/C catalyst would be potential candidates for use as cathode catalyst in PEFC.

We synthesized seven partially protonated poly(aspartic acids)/sodium polyaspartates (P-Asp) with different average molecular weights to study their proton transport properties.

Poly(aspartic acid) and its thin film were synthesized to study proton transport properties. The proton conductivity of the thin film is one order of magnitude higher than that of the pelletized Poly(aspartic acid). The activation energies for the proton conduction of the pelletized Poly(aspartic acid) and thin film are 0.65 and 0.53 eV, respectively.

The electronic structure near the top of the valence band and the bottom of the conduction band for Sr-doped LaScO3 single crystal was investigated by X-ray absorption spectroscopy (XAS).

The iridium oxide nanoparticles supported on Vulcan XC-72 porous carbon were prepared for cathode catalyst in polymer electrolyte fuel cell (PEFC). The catalyst has been characterized by transmission electron microscopy (TEM) and in PEFC tests. The iridium oxide nanoparticles, which were uniformly dispersed on carbon surface, were 2–3 nm in diameter. With respect to the oxygen reduction reaction (ORR) activity was also studied by cyclic voltammetry (CV), revealing an onset potential of about 0.6 V vs. an Ag/AgCl electrode. The ORR catalytic activity of this catalyst was also tested in a hydrogen–oxygen single PEFC and a power density of 20 mW cm−2 has been achieved at the current density of 68.5 mA cm−2. This study concludes that carbon-supported iridium oxide nanoparticles have potential to be used as cathode catalyst in PEFC.

Proton transport properties of three thin films (110, 240, and 360 nm thick films) on R-plane (1102) sapphire substrates for oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] were investigated. The maximum proton conductivity of the thin film is 1.7 × 10-3 S cm-1 at the RH of 80%, which is five times higher than that of the bulk sample (3.0 × 10-4 S cm-1). The activation energies of the 110, 240, and 360 nm thick films are found to 0.74, 0.67, and 0.68 eV at the RH of 80%, respectively.

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films.

A novel proton-conductive copper coordination polymer, (H5C2)2dtoaCu (R2dtoaH2 = dithiooxamide derivatives), was synthesized. The proton conductivity (σp) was 4.2 × 10−6 S cm−1 under the RH of 100% and the ionic transport number was more than 0.99. The σp of (HOH4C2)2dtoaCu was two orders of magnitude higher than that of (H5C2)2dtoaCu, which would be derived from the existence of-OH groups in the alkyl substituent R.

A new copper coordination polymer, (HOC3H6)(2)dtoaCu (dtoa = dithiooxamide), was synthesized. The a.c. conductivity measurements with an impedance analyzer were carried out for (HOC3H6)(2)dtoaCu in order to estimate the proton conductivity (sigmap).

AC conductivity measurements were carried out for a two-dimensional coordination polymer, N,N′-bis-(2-hydroxyethyl)dithiooxamidatocopper(II) with an impedance analyzer in order to estimate the protonic conductivity. This polymer was found to exhibit a high protonic conduction of σp=1.2×10−5 S cm−1 under relative humidity of 83% and 300 K.

Room-temperature proton conductivity, coordination geometry, and pore-diameter distribution of the title Cu(II) coordination polymer have been investigated by AC conductivity, EXAFS, and N2 adsorption isotherm measurements. The AC proton conductivity (σp) obtained from Cole–Cole plot analysis under relative humidity of 75% and 300 K exhibits a considerable high value of as a room-temperature σp. The mechanism of proton conduction seems to be similar to that of a proton-exchange membrane, Nafion, which contains much cluster of water molecules in the porous space of the polymer. The present Cu coordination polymer was revealed to possess porous space of about 6 Å, which includes much water molecules more than 10H2O per unit cell. The dimeric Cu(II) square-planar coordination geometry was confirmed by EXAFS analysis using synchrotron radiation source at SPring-8.

AC conductivity measurements with an impedance analyzer were carried out for a hydrogen-doped coordination polymer, N , N '-bis-(2-hydroxyethyl)dithiooxamidatocopper(II), in order to estimate the protonic condctivity. The log †proton conductiivty was linearly increased from 2.6x10-9 to 2.2 x 10-6 S cmwith relative humidity (RH) from 45 to 100% at 300 K. A slight hysteresis of protonic conductivity was observed upon increasing and decreasing RH, which implies that H3O+ is generated by a reaction between water molecule and acid-base polymer near RH∼100%.