Hidenobu Shiroishi

Sensitization of TiO2 particles by dyes to achieve H2 evolution by visible light

Abstract Sensitization of titanium dioxide particles platinized and suspended in water was carried out by Ru(bpy) 3 2+ , tris(bipirimidine)Ru(II) (Ru(bpym) 3 ) and porphines to induce dihydrogen evolution by visible light in the presence of sacrificial electron donor, EDTA. It was found that Ru(bpym) 3 2+ is an efficient sensitizer for H 2 formation. High concentration of the Ru(bpy) 3 2+ was required to achieve the photosensitization suggesting adsorption of the sensitizer on the TiO 2 . Photochemical deposition of platinum from K 2 [PtCl 4 ] was important to prepare active Pt-loaded TiO 2 photocatalyst. Simple mixing of the TiO 2 and Pt powders in a mortar as usually done for preparing conventional photocatalyst was not effective for the present system showing that electronic channeling between the TiO 2 bulk and the Pt is more important than for usual photocatalysts. The H 2 evolution showed an optimum point at pH 7, which was interpreted by the adsorption of the dye on TiO 2 . For the tetrakis(4-carboxyphenyl)porphine and tetrakis(4-sulfonicphenyl)porphine sensitizers, only the absorption of light at Q band was effective.

Shell-Core Type Proton Conducting TiP2O7-Based Solid Electrolytes

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.

New CO tolerant electro-catalysts exceeding Pt–Ru for the anode of fuel cells

Novel types of CO tolerant electro-catalysts from Pt and organic metal complexes that are far superior to Pt-Ru and practically usable as anode catalysts in reformate gas fuel cells with 100 ppm CO tolerance have been developed.

A simple biofuel cell cathode with human red blood cells as electrocatalysts for oxygen reduction reaction

A red blood cell (RBC) from human exhibited direct electron transfer (DET) activity on a bare indium tin oxide (ITO) electrode. A formal potential of -0.152 V vs. a silver-silver chloride saturated potassium chloride (Ag|AgCl|KCl(satd.)) was estimated for the human RBC (type AB) from a pair of redox peaks at around 0.089 and -0.215 V (vs. Ag|AgCl|KCl(satd.)) on cyclic voltammetric (CV) measurements in a phosphate buffered saline (PBS; 39 mM; pH 7.4) solution. The results agreed well with those of a redox couple for iron-bearing heme groups in hemoglobin molecules (HbFe(II)/HbFe(III)) on the bare ITO electrodes, indicated that DET active species were hemoglobin (Hb) molecules encapsulated by a phospholipid bilayer membrane of the human RBC. The quantity of electrochemically active Hb in the human RBC was estimated to be 30 pmol cm(-2). In addition, the human RBC exhibited oxygen reduction reaction (ORR) activity in the dioxygen (O2) saturated PBS solution at the negative potential from ca. -0.15 V (vs. Ag|AgCl|KCl(satd.)). A single cell test proved that a biofuel cell (BFC) with an O2|RBC|ITO cathode showed the open-circuit voltage (OCV) of ca. 0.43 V and the maximum power density of ca. 0.68 μW cm(-2).

Oxygen Reduction Electrode Properties of Pyrochlores Ln2Ru2O7-δ(Ln=Pr, Nd, Sm) in Aqueous Solutions

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.

Effects of the Substitution of Β-Site Ion on Oxygen Reduction Electrode Properties of Pb2Ru2O7- δ in Aqueous Solutions

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.

Quasi-solid medium for photoinduced charge separation

Abstract New quasi-solid was proposed as a medium for photoinduced charge separation. Photoinduced charge separation and hydrogen production with the new quasi-solid medium using polysaccharide has been investigated. The new medium is a quasi-solid polysaccharide containing a large quantity of water. This medium is tight and elastic solid, obtained by cooling an aqueous solution of a polysaccharide (agarose or κ-carrageenan in this paper) to room temperature after it was dissolved in water by heating. When the quasi-solid (agarose or κ-carrageenan) involving sacrificial electron donor ethylenediaminetetraacetate (EDTA), tris(2,2′-bipyridine)ruthenium complex ([Ru(bpy) 3 ] 2+ ) and methylviologen (MV 2+ ) was irradiated with visible light, methylviologen cation radical (MV + ) was formed. The formation rate of methylviologen cation radical in an agarose solid was faster than that in a κ-carrageenan one. Photoinduced hydrogen production was achieved with this system containing additionally proton reduction catalyst such as platinum black (Pt black), platinum oxide (PtO 2 ), and ruthenium oxide (RuO 2 ). The characteristics of this solid medium for photochemical reactions were discussed.

Photoinduced charge separation at polymer-solution interface

Abstract Photoinduced charge separation using electrostatic repulsion between an anionic polymer film (Nafion) and an anionic sensitizer aqueous solution has been studied for the photoproduction of dihydrogen from proton. It was found that only anionic sensitizers were effective to photoproduce cation radical (MV +) in the anionic polymer film, while cationic sensitizers were not effective. The initial formation rate of MV + by tris(bathophenanthroline)ruthenium (Ru(bpds)34−) sensitizer was faster than that by tris(4,4′-dicarboxy-2,2′-bipyridine)ruthenium (Ru(dcbpy)34−). The presence of anthracene in the Nafion increased the total amount of MV + species because the charge transfer complex formed between anthracene and methylviologen (MV2+) prevents the dimerization of MV +. The formation of MV + dimer is depressed by the coexisting anthracene. The action spectrum for the formation rate of one-electron reduction species agreed with the absorption spectrum of the sensitizer suggesting that an electron transfer from the sensitizer in its MLCT excited state to the MV2+ induces the photochemical event.

Characteristics of photoluminescence from ruthenium polypyridyl complexes incorporated into silk

Abstract Characteristics of photoluminescence from polypyridine Ru complexes incorporated into Bombyx mori silk fibroins with several structures have been investigated. The structures of the silk were α-helix, silk I, and silk II, that involve only intra-, both intra- and inter-, and only inter-molecular hydrogen bonds, respectively. Microenvironment in the silk was studied using photoluminescence probe. Maximum wave number of probes in silk was shifted to higher energy than that in water. The wave number decreased in the order, α-helix>silk I>silk II, suggesting that the polarity of the microenvironment is in the order, α-helix

Development of Oxygen Reduction Electrocatalysts Based on Manganese Oxides for AEMFCs

Perovskite and Mn oxide nanosheet-based electrocatalysts were synthesized as the cathode of anion-exchange membrane fuel cells (AEMFCs), and their oxygen reduction reaction (ORR) activities and AMFC performances were evaluated. Perovskite La0.6Sr0.4MnO3 (LS0.4M/KB) loaded on Ketjen Black exhibited the highest ORR activity (onset potential: ca. 0.9 V vs. reversible hydrogen electrode (RHE) and efficiency for 4-electron reduction of O2: > 90%), and achieved a maximum power density of ca. 92 mW cm-2.