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A Mg2+-containing MOF was synthesized through ion exchange with an anionic framework. The Mg2+-containing MOF showed high ionic conductivity under a guest vapor at ambient temperature.

Catalytic support effects have been widely studied as a key factor for creating highly active heterogeneous catalysts with limited amounts of rare metal elements. Recently, support effects of metal-organic frameworks (MOFs) started to be investigated using their wide variety in pore size, electronic state, and selective adsorption property. Three types of support effects, namely molecular sieving, charge transfer, and substrate adsorption effects, have been reported on composite catalysts of metal nanoparticles supported on MOFs (M/MOFs). The current reports on heterogeneous catalysis in M/MOFs clearly demonstrated that both catalytic activity and product selectivity can be drastically enhanced and modulated by MOF supports through these support effects, and that application of MOFs as the supports is beneficial for creating novel high performance catalysts with metal nanoparticles. This minireview summarizes the catalytic properties and support effects observed on M/MOFs.

A Mg2+-conductive MOF was created with small-sized three-dimensional pores. The sample showed superionic conductivity at room temperature under guest vapors.

Layer flexibility in two-dimensional coordination polymers (2D-CPs) contributes to several functional materials as it results in anisotropic structural response to external stimuli. Chemical modification is a common technique for modifying layer structures. This study demonstrates that crystal morphology of a cyanide-bridged 2D-CP of type [Mn(salen)]2 [ReN(CN)4 ] (1) consisting of flexible undulating layers significantly impacts the layer configuration and assembly. Nanoplates of 1 showed an in-plane contraction of layers with a longer interlayer distance compared to the micrometer-sized rod-type particles. These effects by crystal morphology on the structure of the 2D-CP impacted the structural flexibility, resulting in dual-functional changes: the enhancement of the sensitivity of structural transformation to water adsorption and modification of anisotropic thermal expansion of 1. Moreover, the nanoplates incorporated new adsorption sites within the layers, resulting in the uptake of an additional water molecule compared to the micrometer-sized rods.

This is a first report on a novel approach for a significant enhancement in the ionic conductivity of Mg ions in solid, induced by organic vapor. The Mg ions located inside the pores of a metal–org...

In the title compound (systematic name: 3,8-diamino-5-ethyl-6-phenylphenanthridin-5-ium 2,2,3,3,4,4,4-heptafluorobutyrate), C21H20N3 +·C4F7O2 −, two ethidium ions, C21H20N3 + form a dimerized structure due to π–π interactions, even though they are positively charged. The heptafluorobutyrate anions are connected to neighbouring cation dimers via hydrogen-bonding interactions, the hydrogen-bonding donor sites of the –NH2 groups of the ethidium ions connecting to the hydrogen-bonding acceptor sites of the –COO− groups of the heptafluorobutyrate anions.

We present a systematic study on the support effect of metal-organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH2, UiO-66-NH2, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH2 and MIL-125-NH2) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH2 showed a remarkably high EtOH yield (31% at 200 degrees C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO2, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH2 support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH.

We first report a solid-state crystalline "Mg

Iridium oxide (IrOx)-based materials are the most suitable oxygen evolution reaction (OER) catalysts for water electrolysis in acidic media. There is a strong demand from industry for improved perf...

The 2D coordination polymers, [Mn(salen)]2[PtII(CN)4]1-x[PtIV(CN)4(I2)]x (salen = N,N'-ethylenebis(salicylideneaminato), x = 0.18 (1), 0.45 (2), 0.85 (3)), have been synthesized via consecutive oxidative additions of iodine to the 2D undulating layers in [Mn(salen)]2[PtII(CN)4]. The presence of I-Pt-I chains perpendicular to the layers and the inhomogeneity of individual I-Pt-I sites were demonstrated. The I-Pt-I chains in 3 give rise to an absorption band involving the excitation that arises from an antibonding nature orbital to the corresponding bonding nature orbital between iodides in the I-Pt-I bridging units. Moreover, variable-temperature X-ray powder diffraction patterns and Raman spectra for 1 and 2 indicate that some I-Pt-I sites display different vibrational energies that are associated with the contraction of the zigzag 2D layers.

Ti1−xZrxO2 complex oxide particles with 0.02 ≤ x ≤ 0.1 show superior catalytic performances for the direct power storage into glycolic acid via electroreduction of oxalic acid. The atomic pair distribution function analysis of X-ray total scatterings suggested that structural periodicity is the key factor for the catalytic enhancement.

Electrochemical hydrogenation of a carboxylic acid using water as a hydrogen source is an environmentally friendly synthetic process for upgrading bio-based chemicals. We systematically studied electrochemical hydrogenation of non-aromatic carboxylic acid derivatives on anatase TiO2 by a combination of experimental analyses and density functional theory calculations, which for the first time shed light on mechanistic insights for the electrochemical hydrogenation of carboxylic acids. Development of a substrate permeable TiO2 cathode enabled construction of a flow-type electrolyser, i.e., a so-called polymer electrode alcohol synthesis cell (PEAEC) for the continuous synthesis of an alcoholic compound from a carboxylic acid. We demonstrated the highly efficient and selective conversion of oxalic acid to produce glycolic acid, which can be regarded as direct electric power storage into an easily treatable alcoholic compound.

Metal–organic frameworks (MOFs) have emerged as a new class of ionic conductors because of their tuneable and highly ordered microporous structures. The ionic conduction of various ionic carriers, such as a proton (H+), hydroxide ion (OH−), lithium ion (Li+), sodium ion (Na+), and magnesium ion (Mg2+), in the pores of MOFs has been widely investigated over the past decade. Reports reveal that the porous or channel structures of MOFs are fundamentally suitable as ion-conducting pathways. There are clear differences in the basic designs of ion-conductive MOFs, i.e., the introduction of ionic carriers and construction of efficient ion-conducting pathways, depending on the ionic carriers. We summarize the examples and fundamental design of highly ion-conductive MOFs with various types of ionic carriers.

We newly synthesized an anionic porous MOF, UiO-67-NSO2CF3 ((HPy)6[Zr6O4(OH)4(BPDC-NSO2CF3)6](guest)n (H2BPDC-NSO2CF3 = (4,4′-dicarboxy-[1,1′-biphenyl]-2-yl)((trifluoromethyl)sulfonyl)amide, HPy+ = pyridinium), having large pore size through post-synthetic method. The amino groups (–NH2) on the UiO-67-NH2 were converted into –NSO2CF3– groups. The sample was characterized with X-ray powder diffraction, scanning electron microscope observations, SEM combined with energy-dispersive X-ray spectroscopy, infrared spectra, thermogravimetry, and N2 adsorption isotherms measurements. These measurements revealed that the successful synthesis of the porous MOF, UiO-67-NSO2CF3.

A coordination polymer of formula [Cu(μ 1,3-N3)2(imH)2] n (1) has been synthesized by reaction of Cu(NO3)2 with imidazole and sodium azide in CH3OH/CH3CN. The complex was characterized by FTIR, elemental analysis, powder diffraction, thermogravimetric analysis, magnetic measurements, and single-crystal X-ray diffraction. The X-ray crystal structure shows that the Cu(II) centers have a distorted octahedral coordination geometry, being coordinated by two imidazole ligands at the trans positions. Each azide links two [Cu(imH)2]2+ units to form 1D zigzag chains. Variable-temperature magnetic susceptibility studies at low field reveal dominant intrachain ferromagnetic/antiferromagnetic interactions. Using a model with n = 10, the coupling parameters J AF = −2.95 and J F = 17.99 with g = 2.12 have been determined.

Compounds [CuII 2(benz)4(Hbenz)2] (1) and [CuII(ppa)2(H2O)2] n (2), where benz = benzoate and ppa = 3-pyridinepropionic acid, were synthesized and studied for their 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and the inhibition of enzymes such as acetylcholinesterase (AChE), butyrylcholinesterase (BChE), lipoxygenase (LOX), urease, chymotrypsin and α-glucosidase. The synthesized compounds were also studied by hemolytic method for their cytotoxicity and found to be low-toxicity substances. For AChE inhibition, compound 2 showed IC50 = 31.22 ± 0.45 μM, as compared to compound 1with IC50 = 36.52 ± 0.44 μM. Both compounds showed comparably low activity against BChE and were also active against urease, but compound 1 exhibited selective anti-urease activity. The anti-α-glucosidase activity of both compounds was comparable with that of standard drug used.

For a rhodium ion-modified TiO2 (Rh3+/TiO2) photocatalyst responding to visible light, control of the structure of the Rh3+ modifier and effects of the structures of the Rh3+ modifier on photocatalytic activities were examined. A TiO2 support was pre-calcined to maintain crystallinity and specific surface area during post-calcination, and the structure of the Rh3+ modifier for Rh3+/TiO2 was changed by post-calcination without causing changes in the crystallinity and specific surface area of the TiO2 support. In mineralization of acetone under irradiation of visible light, the photocatalytic activities of the post-calcined Rh3+/TiO2 showed a volcano-like tendency as a function of post-calcination temperature. The results of this study showed that an atomically isolated structure of the Rh3+ modifier was preferable for high activities and that aggregation of the Rh species led to a decrease in the activities.

Wide band gap of pure ZnO with wurtzite crystal structure (3.1–3.4 eV) limits its photocatalytic activity to the ultraviolet (UV) region of solar spectrum. High-pressure rocksalt polymorph of ZnO can theoretically show narrow band gap; however, the rocksalt phase is unstable at ambient pressure. Herein, rocksalt phase with large fractions of oxygen vacancies is successfully stabilized at ambient conditions by inducing plastic strain in pure ZnO under 6 GPa using the High-Pressure Torsion (HPT) method. Formation of rocksalt phase reduces the band gap of ZnO to 1.8 eV, which is in good agreement with the first-principles calculations, and significantly improves the photocatalytic activity under visible light.

Despite many advancements, an inexpensive ammonia synthesis catalyst free from hydrogen and nitrogen poisoning, and capable of synthesizing ammonia under mild conditions is still unknown and is long sought-after. Here we present an active nanoalloy catalyst, RuFe, formed by alloying highly active Ru and inexpensive Fe, capable of activating both N2 and H2 without blocking the surface active sites and thereby overcoming the major hurdle faced by the current best performing pure metal catalysts. This novel RuFe nanoalloy catalyst operates under milder conditions than the conventional Fe catalyst and is less expensive than the so far best performing Ru-based catalysts providing additional advantages. Most importantly, by integrating theory and experiments, we identified the underlying mechanisms responsible for lower surface poisoning of this catalyst, which will provide directions for fabricating poison-free efficient NH3 synthesis catalysts in future.

The layered P2-Nax MO2 (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2-Nax CoO2 created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm(-1) at 25 °C. Using in situ synchrotron X-ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na0.61 (H3 O)0.18 Co0.93 O2 . Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co-stoichiometric compound Nax (H3 O)y CoO2 does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.

Proton-conductive electrolytes are key materials in fuel cells. We introduced acidic functional groups into a porous coordination polymer (PCP), or metal–organic framework (MOF), and constructed pr...

The arc plasma deposition (APD) method is first applied to prepare metal-organic framework (MOF) composites loading metal nanoparticles having a direct contact with the MOF. We demonstrate the detailed growth mechanism of metal particles on the MOFs and the applicability of the APD for various combinations of metals and MOFs.

We demonstrate the production of glycolic acid, an industrially important alcoholic compound, via the electrochemical reduction of oxalic acid, which is procurable from biomass, and electro-oxidation of water with the help of renewable light energy for the first time. In principle, this new synthesis system is achievable while minimizing the consumption of fossil resources. We built a precious-metal free electrosynthesis system by employing a TiO2 cathode for oxalic acid reduction and a WO3 photoanode for water oxidation. The alcohol production proceeds during the application of electric power above 2.1 V in the dark. Notably, UV-visible light irradiation of the WO3 photoanode enables glycolic acid electrosynthesis above 0.5 V, which is lower (by 0.6 V) than the theoretical bias, i.e., 1.1 V. Glycolic acid electrosynthesis with an 80% high Faradaic efficiency was achieved on applying a bias of 1.5 V under UV-visible irradiation (λ > 300 nm).

Electroreduction of CO 2 has potential for storing otherwise wasted intermittent renewable energy, while reducing emission of CO 2 into the atmosphere. Identifying robust and efficient electrocatalysts and associated optimum operating conditions to produce hydrocarbons at high energetic efficiency (low overpotential) remains a challenge. In this study, four Cu nanoparticle catalysts of different morphology and composition (amount of surface oxide) are synthesized and their activities towards CO 2 reduction are characterized in an alkaline electrolyzer. Use of catalysts with large surface roughness results in a combined Faradaic efficiency (46%) for the electroreduction of CO 2 to ethylene and ethanol in combination with current densities of ∼200 mA cm −2 , a 10-fold increase in performance achieved at much lower overpotential (only 2 , as well as the application of gas diffusion electrodes covered with active and rough Cu nanoparticles in the electrolyzer. These high performance levels and the gained fundamental understanding on Cu-based catalysts bring electrochemical reduction processes such as presented here closer to practical application.

Closed–open structural transformations in flexible metal–organic frameworks (MOFs) are of interest for potential applications such as separation, because of their complete selectivity for the adsorption of specific guest molecules. Here, we report the control of the adsorption behaviour in a series of flexible MOFs, (H2dab)[M2(ox)3] (H2dab = 1,4-diammoniumbutane, M = Fe, Co, Ni, Zn, or Mg), having different central metals with analogous crystal structures. We found that a significant change in the selective adsorption behaviour for EtOH over MeCHO and MeCN is caused by the type of central metals, without changes in the crystal structures of all phases (except the Ni compound). A systematic study of adsorption measurements and structural analyses of the analogous MOFs reveals for the first time that the framework flexibility around the central metals of MOFs is truly related to the selective adsorption behaviour.

Reaction of copper(II) nitrate trihydrate with N,N-dimethylethanolamine (dmea) and pivalic acid in methanol led to the hexanuclear copper(II) complex Cu6(η1:μ2-C4H10NO)4(η1:η1:μ2-C5H9O2)4(η1:μ1-C5H9O2)2(μ3-OH)2 (1). The crystal structure of 1 indicates that hexametallic centers are bridged by the μ3-alkoxo, dmea oxygens, and the μ2-dicarboxylato oxygen atoms of pivalate ions. Furthermore, in the asymmetric unit, three types of copper ions have been found labeled as Cu1, Cu2 and Cu3. The Cu2 takes a distorted octahedral shape, whereas Cu1 and Cu3 adopt square pyramidal geometries. The complex 1 shows strong antiferromagnetic interactions through the oxo groups within the dimeric units (J = − 82.6 to − 25.8 cm− 1) and weak antiferromagnetic couplings between the dimers (J = − 10.9 and 0.8 cm− 1).

We newly synthesized an amino-functionalized zeolitic imidazolate framework (ZIF), [Zn{(dmamIM)n(mIM)m}2]∞ (dmamIM−: 2-[(dimethylamino)methyl]imidazolate; mIM−: 2-methylimidazolate), through a liga...

Proton conductivity in solids is of importance not only for useful applications such as fuel cells but also for better understanding of the nature of proton-transport phenomena. Recently, metal–organic frameworks (MOFs) have been emerged as a novel class of proton-materials because the ability to rationally design and chemically tune their architecture allows chemists to establish various methods to control the proton conductivity. We have proposed three types (types I–III) of concepts to give high proton conductivity to MOFs. In type I, proton carriers are introduced as counterions into the pores (e.g., H3O+). In type II, acidic groups are placed on the framework (e.g., –COOH). In type III, charge-neutral proton-conducting species are incorporated within the pores (e.g., H3PO4).1 We have synthesized (NH4)2(adp)[Zn2(ox)3]·3H2O (adp = adipic acid; ox = oxalate), having both type I and type III features; (NH4)2(adp)[Zn2(ox)3]·3H2O shows high proton conductivity because of the existence of two-dimensional (2-D) hydrogen-bonding networks which act as a crystalline proton-conducting pathways.2 Intentional control of proton conductivity and the proton dynamics in this MOF has been also studied. On another front, hydroxide-ion conductors have received a great deal of interest as electrolytes for alkaline fuel cells that can operate without precious metal catalysts such as Pt. We have also focused on creating novel hydroxide ion conductors using the MOFs. We proposed a new strategy to introduce hydroxide ions into MOFs, i.e., which is “hydroxide salt inclusion into alkaline-stable MOFs”. We succeeded in synthesizing a novel MOF including alkylammonium hydroxide salt by employing an alkaline-stable ZIF-85 framework (NBu4-ZIF-8-OH) (Figure 1).6 ,7 Ionic conductivity of NBu4-ZIF-8-OH was found to be 2.3 × 10–8 S cm–1 at maximum, which is four orders of magnitude higher than that of blank ZIF-8. Considering that the framework structure of NBu4-ZIF-8-OH is the same as that of ZIF-8, the enhancement in the ionic conductivity can be attributed to the included salt. (References) (1) M. Sadakiyo et al., J. Am. Chem. Soc. 2009, 131, 9906. (2) M. Sadakiyo et al., J. Am. Chem. Soc. 2014, 136, 7701. (3) M. Sadakiyo et al., J. Am. Chem. Soc. 2014, 136, 13166. (4) S. Miyatsu, M. Kofu, O. Yamamuro, M. Sadakiyo, T. Yamada, H. Kitagawa et al., Phys. Chem. Chem. Phys. 2014, 16, 17295. (5) Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. PNAS 2006, 103, 10186. (6) M. Sadakiyo et al., J. Am. Chem. Soc. 2014, 136, 1702. (7) M. Sadakiyo et al., Chem. Lett. 2017, 46, 1004. Figure 1

Porous crystalline metal–organic frameworks (MOFs) are emerging as a new class of proton conductors through the hydrogen-bonded degenerate system., Porous crystalline metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are emerging as a new class of proton conductors with numerous investigations. Some of the MOFs exhibit an excellent proton-conducting performance (higher than 10–2 S cm–1) originating from the interesting hydrogen(H)-bonding networks with guest molecules, where the conducting medium plays a crucial role. In the overwhelming majority of MOFs, the conducting medium is H2O because of its degenerate conjugate acid–base system (H3O+ + H2O ⇔ H2O + H3O+ or OH– + H2O ⇔ H2O + OH–) and the efficient H-bonding ability through two proton donor and two acceptor sites with a tetrahedral geometry. Considering the systematic molecular similarity to water, ammonia (NH3; NH4+ + NH3 ⇔ NH3 + NH4+) is promising as the next proton-conducting medium. In addition, there are few reports on NH3-mediated proton conductivity in MOFs. In this perspective, we provide overviews of the degenerate water (hydronium or hydroxide)- or ammonia (ammonium)-mediated proton conduction system, the design strategies for proton-conductive MOFs, and the conduction mechanisms.

We introduce a power circulation system using redox reactions of glycolic acid (GC), a monovalent alcoholic compound, and oxalic acid (OX), a divalent carboxylic acid for the efficient circulation of renewable electricity. Electric power is efficiently accumulated in GC via four-electron reduction of OX on TiO2 electrodes. Mapping for phases of TiO2 using electron energy-loss spectroscopy revealed that anatase-type TiO2 particles exhibit superior catalytic activities, i.e. highly selective electroreduction of OX to produce GC, compared to rutile-type ones. GC was successfully produced on porous TiO2 spheres purely composed of the anatase phase under mild conditions in the potential region of −0.5 to −0.7 V versus the RHE at 50 °C with high efficiency and selectivity (70–95% Faradaic efficiency and >98% selectivity). Direct transformation of solar energy into chemical energy in GC was also achieved using a photo-assisted electrochemical cell employing oxide semiconductor photoelectrodes as the anode for water oxidation and TiO2 cathode for OX reduction. A liquid flow-type electrolyzer that continuously produces GC from OX was constructed by employing a polymer electrolyte electrolyzer, named a polymer electrolyte alcohol electrosynthesis cell (PEAEC). Porous anatase TiO2 directly grown on Ti mesh (TiO2/Ti-M) was newly fabricated as the cathode electrode having favourable substrate diffusivity. A membrane electrode assembly composed of the TiO2/Ti-M, Nafion and an IrO2 supported on a gas-diffusion carbon electrode (IrO2/C) was applied to the PEAEC. The PEAEC achieves a maximum energy conversion efficiency of 49.6% or a continuous 99.8% conversion of 1 M OX, which is an almost saturated aqueous solution at room temperature. Electronic power generation via electro-oxidation of GC was demonstrated. The catalytic activity test on various metal materials revealed that Rh, Pd, Ir and Pt have preferable features as a catalyst for GC electro-oxidation, and Pt exhibits the highest catalytic activity. A carbon-supported Pt catalyst (Pt/C) in alkaline conditions, especially in LiOH aq., showed higher activity, durability and product selectivity for electro-oxidation of GC rather than those in acidic media. These efforts will contribute to efficient utilization of renewable electricity.

We demonstrate electric power generation via the electrooxidation of ethylene glycol (EG) on a series of Fe-group nanoalloy (NA) catalysts in alkaline media. A series of Fe-group binary NA catalysts supported on carbon (FeCo/C, FeNi/C, and CoNi/C) and monometallic analogues (Fe/C, Co/C, and Ni/C) were synthesized. Catalytic activities and product distributions on the prepared Fe-group NA catalysts in the EG electrooxidation were investigated by cyclic voltammetry and chronoamperometry, and compared with those of the previously reported FeCoNi/C, which clarified the contributory factors of the metal components for the EG electrooxidation activity, C2 product selectivity, and catalyst durability. The Co-containing catalysts, such as Co/C, FeCo/C, and FeCoNi/C, exhibit relatively high catalytic activities for EG electrooxidation, whereas the catalytic performances of Ni-containing catalysts are relatively low. However, we found that the inclusion of Ni is a requisite for the prevention of rapid degradation due to surface modification of the catalyst. Notably, FeCoNi/C shows the highest selectivity for oxalic acid production without CO2 generation at 0.4 V vs. the reversible hydrogen electrode (RHE), resulting from the synergetic contribution of all of the component elements. Finally, we performed power generation using the direct EG alkaline fuel cell in the presence of the Fe-group catalysts. The power density obtained on each catalyst directly reflected the catalytic performances elucidated in the electrochemical experiments for the corresponding catalyst. The catalytic roles and alloying effects disclosed herein provide information on the design of highly efficient electrocatalysts containing Fe-group metals.

The establishment of an efficient electric power distribution method is the key to realising a sustainable society driven by renewable-energy-based electricity, such as solar photovoltaics, wind turbine, and wave electricity, in view of supply instability. Here, we demonstrate an electric power circulation method that does not emit CO2 and is based on the glycolic acid (GC)/oxalic acid (OX) redox couple. Direct electric power storage in GC ensures considerably high energy density storage and good transportability through OX electroreduction with significantly high selectivity (>98%) using pure anatase-type titania (TiO2) spheres under mild conditions in the potential region of −0.5 to −0.7 V vs. the RHE at 50 °C. The most desirable characteristic of this electroreduction is the suppression of hydrogen evolution even in acidic aqueous media (Faraday efficiency of 70–95%, pH 2.1). We also successfully generated power without CO2 emissions via selective electrooxidation of GC with an alkaline fuel cell.

We succeeded in the efficient preparation of well-dispersed Fe-Co nanoalloys (NAs) using the arc plasma deposition method. Synchronous shots of dual arc plasma guns were applied to a carbon support to prepare the solid-solution type Fe-Co NAs having an approximately 1 : 1 atomic ratio. The alloy structures with and without a reductive thermal treatment under a hydrogen atmosphere were examined using X-ray powder diffraction, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray analysis, high resolution STEM, and magnetic measurements, suggesting that highly crystalline spherical particles of ordered B2-type Fe-Co NAs form by the thermal treatment of the deposited grains.

We newly synthesized a metal–organic framework (MOF) Rb2(adp)[Zn2(ox)3]·3H2O (adp = adipic acid; ox2 − = oxalate), where the rubidium ions, carboxylic acid groups, and water molecules are located in an interlayer space of a two-dimensional (2-D) oxalate-bridged network. The structure of this compound was determined using single-crystal X-ray diffraction analysis. Hydrated phases of this compound were examined using thermogravimetry and water vapor adsorption measurements. Proton conductivity in this MOF was investigated by alternating current impedance measurements. Systematic comparison with previously reported isomorphous 2-D compounds A2(adp)[Zn2(ox)3]·3H2O (A = NH4 and K) showed that the difference in the ionic radii of the cations leads to a difference in activation energy of proton conductivity and that absence of NH4+ ions causes a significant decrease in proton conductivity, even though the ionic radius of Rb+ (1.52 A) is closer to that of NH4+ (1.61 A) than that of K+ (1.38 A).

A liquid flow-type electrolyser that continuously produces an alcohol from a carboxylic acid was constructed by employing a polymer electrolyte, named a polymer electrolyte alcohol electrosynthesis cell (PEAEC). Glycolic acid (GC, an alcoholic compound) is generated on anatase TiO2 catalysts via four-electron reduction of oxalic acid (OX, a divalent carboxylic acid), accompanied with water oxidation, which achieves continuous electric power storage in easily stored GC. Porous anatase TiO2 directly grown on Ti mesh (TiO2/Ti-M) or Ti felt (TiO2/Ti-F) was newly fabricated as a cathode having favourable substrate diffusivity. A membrane-electrode assembly composed of the TiO2/Ti-M, Nafion 117, and an IrO2 supported on a gas-diffusion carbon electrode (IrO2/C) was applied to the PEAEC. We achieved a maximum energy conversion efficiency of 49.6% and a continuous 99.8% conversion of 1 M OX, which is an almost saturated aqueous solution at room temperature.

We employed metal-organic framework (MOF) supports to modulate the electronic states of loaded Pt nanoparticles (NPs) in their composite catalysts (Pt/MOFs). Pt NPs were homogenously deposited on four MOFs characterized with different electronic states (Zn-MOF-74, Mg-MOF-74, HKUST-1, and UiO-66-NH2). Theoretical and experimental studies demonstrated that a charge-transfer interaction between Pt NPs and MOFs is a critical factor for controlling the catalytic activity of Pt NPs supported on MOFs.

Increase of CO2 concentration in the atmosphere is one of reasons for the global warming. Development of energy circulation systems, which do not emit CO2 in the atmosphere, is an emergent issue for present-generation scientists [1]. As an answer, we have proposed a new type of energy circulation system, namely, carbon-neutral energy (CN) cycle. With a practical application in mind, three limitations are imposed on the CN cycle; (1) no CO2 emissions, (2) utilization of liquid fuels and (3) minimizing the use of precious metal catalysts. In anticipation of a practical use in the near future, an alkaline fuel cell will be adapted for the CN cycle where non-platinum catalysts can work. For our purpose, electric power will be generated by partial oxidation of alcohols to carboxylic acids.[2] In view of ease in handling, fuels having a high boiling point (b.p.) are favorable for the CN cycles. To this end, glycol (EG) of which b.p. is 470 K an ideal candidate as a fuel. In this case, an oxidized product of EG can be oxalic acid. Compared to the energy obtained by the complete oxidation of EG into CO2, we can derive ca. 80 % of energy even in the partial oxidation of EG to oxalic acid, implying that the EG/oxalic cycle possibly works as an energy cycle. We herein show an example of selective EG oxidation catalysts working in alkaline conditions.

Structure-defined metal-organic frameworks (MOFs) are of interest because rational design and construction allow us to develop good proton conductors or possibly control the proton conductivity in solids. We prepared a highly proton-conductive MOF (NH4)2(adp)[Zn2(ox)3]·nH2O (abbreviated to 1·nH2O, adp: adipic acid, ox: oxalate, n = 0, 2, 3) having definite crystal structures and showing reversible structural transformations among the anhydrate (1), dihydrate (1·2H2O), and trihydrate (1·3H2O) phases. The crystal structures of all of these phases were determined by X-ray crystallography. Hydrogen-bonding networks consisting of ammonium ions, water molecules, and carboxylic acid groups of the adipic acids were formed inside the two-dimensional interlayer space in hydrated 1·2H2O and 1·3H2O. The crystal system of 1 or 1·2H2O (P21/c, No. 14) was changed into that of 1·3H2O (P1̅, No. 2), depending on water content because of rearrangement of guests and acidic molecules. Water molecules play a key role in proton conduction as conducting media and serve as triggers to change the proton conductivity through reforming hydrogen-bonding networks by water adsorption/desorption processes. Proton conductivity was consecutively controlled in the range from ∼10(-12) S cm(-1) (1) to ∼10(-2) S cm(-1) (1·3H2O) by the humidity. The relationships among the structures of conducting pathways, adsorption behavior, and proton conductivity were investigated. To the best of our knowledge, this is the first example of the control of a crystalline proton-conducting pathway by guest adsorption/desorption to control proton conductivity using MOFs.

We demonstrate a metal-organic framework (MOF) design for the inclusion of hydroxide ions. Salt inclusion method was applied to an alkaline-stable ZIF-8 (ZIF = zeolitic imidazolate framework) to introduce alkylammonium hydroxides as ionic carriers. We found that tetrabutylammonium salts are immobilized inside the pores by a hydrophobic interaction between the alkyl groups of the salt and the framework, which significantly increases the hydrophilicity of ZIF-8. Furthermore, ZIF-8 including the salt exhibited a capacity for OH(-) ion exchange, implying that freely exchangeable OH(-) ions are present in the MOF. ZIF-8 containing OH(-) ions showed an ionic conductivity of 2.3 × 10(-8) S cm(-1) at 25 °C, which is 4 orders of magnitude higher than that of the blank ZIF-8. This is the first example of an MOF-based hydroxide ion conductor.