Papers by Author: Jun Kuwano

Abstract: Metallic ruthenium nano-particles supported on carbon were prepared from Ru3(CO)12 and highly-porous activated carbon by adsorption of the complex under boiling conditions in an acetone or cyclohexane solution, followed by H2 reduction at 200oC. Occupation of micropores with the precursor all through the carbon surface would diminish the BET surface area and the pore volume, whereas partial restoration of them by heating the material in H2 flow would be caused by complex decomposition and coagulative growth of Ru nano-particles (3.01 nm in average from TEM observation), which were surely lager in size than the pore diameter (2.15 nm determined by adsorption-isotherm measurements). Ru nano-particles were well dispersed on carbon.

Abstract: In order to reproduce the observed ionic conductivities and activation energies computationally, the potential parameters (PMs) were optimized for classical molecular dynamic simulations on Li ion conduction in the A-site deficient perovskite solid solution La056Li0.33TiO3 with disordered A-site ion arrangement. By the use of the optimized PMs, the conductivities and the activation energies were improved considerably from 4.1×10-3 Scm-1 to 4.4×10-2 Scm-1 at 800 K and 0.02 eV to 0.2 eV, respectively. The pair correlation functions calculated with the optimized PMs reveal that the Li-ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-, and that the simulated Li location is significantly related to the conductivity.

Abstract: Shell-core type TiP2O7-based electrolytes were synthesized by a low-temperature sol-gel method, and their conductivities were investigated by ac-impedance spectroscopy. The samples heat-treated at 500°C showed higher proton conductivities of 3.8 × 10-2 - 1 × 10-2 Scm-1 at intermediate temperatures (100 - 300°C). The conductivity decreased by reheat-treatments at 600°C and 700°C due to a decrease in the amount of the conductive amorphous shells. However, the mechanical strength of the sample pellet significantly increased by the reheat-treatment. The sample reheat-treated at 600°C kept high conductivities of 8.8 × 10-3 - 1 × 10-3 Scm-1 in a range of 100°C - 300°C.

Abstract: Phase studies and ac-conductivity measurements were carried out in the compositions M0.8In0.2Li0.2P2O7 [MILP] (M=Sn, Zr, Ti). The bulk conductivities were of the order of ~10-5 Scm-1 at 623 K and higher in the order of TiILP≥ZrILP>SnILP. The activation energies, as expected, became lower in the order of ZrILPSnILP in bulk conductivities were not correlated with that of the activation energies probably because of the impureness of the ZrILP sample.

Abstract: Two series of compositions, BaCe0.8-xGd0.2RuxO3-δ (BCGRx, x=0-0.8) and BaGd1-yRuyO3-δ (BGRy, y=0.5-1.0), were synthesized and their crystal phases were examined. The BCGR0.15 and BGR0.5 oxides were a single phase of perovskite solid solution, while BCGR0.67 and BGR0.67 were a perovskite-related superstructure phase. The onset voltage (Vo) of the reduction current and the efficiency (E4) of the 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In the BCGRx series, the activities for electrochemical oxygen reduction (EOR) increased with increasing Ru content. In the BGRy series, the BGR0.67 superstructure phase showed a higher EOR activity than the perovskite BGR0.5 and the hexagonal(4H) BaRuO3. This indicates that the EOR activity depends on the crystal phase. The BGR0.67 exhibited the best EOR activity of all the samples. The Vo value was 0.80 V vs. reversible hydrogen electrode and the E4 value was almost 100 %.

Abstract: The activities of the pyrochlores Pb2Ru2-xMxO7-δ (M=Mn,Fe,Co,Ni)[PRM(0x)] toward electrochemical oxygen reduction (EOR) were examined in 0.1 M KOH and 0.05 M H2SO4 aqueous solutions. The onset voltage (Vo) and the efficiency (E4) of 4-electron reduction of oxygen for PRM(0x) were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In PRM01, the order of the EOR activities was PRMn01 > PRCo01 > PRNi01 > PRFe01 in both solutions. This was consistent with the variation of the lattice parameters, i.e. PRM01 with a smaller lattice parameter showed higher EOR activity. In addition, PRMn05 showed higher EOR activity than PRMn01. The onset voltages Vo were 0.95 and 0.50 V vs. reversible hydrogen electrode in 0.1 M KOH and 0.05 M H2SO4, respectively, while E4 was almost 100 % in both solutions. These results indicate that the EOR activity of PRM(0x) depends on the incorporated metal ions on the B-sites and their contents.

Abstract: The activity of electrochemical oxygen reduction (EOR) for the pyrochlores Ln2Ru2-XO7-δ (Ln=Pr,Nd,Sm) [LnR] were examined in 0.1 M KOH aqueous solution at 70oC. The onset voltage (Vo) of the oxygen reduction current and the efficiency (E4) of 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. PrR with the highest EOR activity showed Vo = ~ 0.85 V vs. reversible hydrogen electrode and E4 values above 80 %. Their Vo and E4 values show that LnR containing Ln with a smaller atomic number has a higher EOR activity, i.e. the order of the activity is PrR > NdR > SmR. This was in good agreement with that of the lattice parameters of LnR. These results indicate that the EOR activity of LnR depends on the kind and/or the size of the lanthanide metal ion on the A-site. PrR and NdR exhibited higher E4 values than known excellent Pb2Ru2O7-δ electrocatalyst containing toxic Pb.

Abstract: Aligned carbon nanotube arrays (CNTAs) were readily synthesized by a resistance heating method on a substrate of commercially available stainless steel which has more plentiful availability than the wafers of Si and quarts. The catalyst was supported on the substrate by dip coating with a methanol solution of M(C5H5)2(M=Co,Fe), and the substrate was electrically heated at 800oC in methanol. Highly aligned CNTAs were grown from the catalyst prepared from 0.02 M Co(C5H5)2 methanol solution. The alignment was influenced by the concentration and the kind of M(C5H5)2.

Abstract: Vertically aligned carbon nanotubes (CNTs) were grown on a stainless steel substrate (SUS304) by resistance-heating method in alcohols containing homogeneously dissolved cobaltocene Co(C5H5)2 as a catalyst source. Straight-chain primary alcohols, 1,2-ethanediol and cyclohexanol were used as carbon sources to examine the effects of the molecular structures on the morphology of the aligned CNTs. Methanol brought the best purity and alignment of CNTs of all the alcohols. The CNTs from 1,2-ethanediol was worse in the purity than those from ethanol with the same number of carbon atoms. The CNTs from cyclohexanol had a better purity than those from 1-hexanol. Distinctive features of this method are simple, low cost and a one-step process involving none of vacuum processes and catalyst preparation processes.