Kiyofumi Yamagiwa

Fabrication of Carbon-Felt-Based Multi-Enzyme Immobilized Anodes to Oxidize Sucrose for Biofuel Cells

A carbon-felt-based multi-enzyme immobilized bioanode for biofuel cells has been successfully developed. The combination of four enzymes, namely, invertase, mutarotase, glucose oxidase, and fructose dehydrogenase, makes it possible to use sucrose--a disaccharide--as fuel for the bioanode. The new electrode exhibits a high oxidation current density of about 12 mA cm(-2) (0.25 V vs. Ag/AgCl) in a McIlvaine buffer solution containing sucrose at pH 6.0 in the half-cell configuration. A sucrose/O(2) biofuel cell composed of the bioanode and an opposite biocathode, including bilirubin oxidase as the enzymatic electrocatalyst, was fabricated, and the new device demonstrated a maximum power density of 2.90 mW cm(-2) with an open-circuit voltage of 0.69 V in the McIlvaine buffer solution. The biofuel cell fabricated using our multi-enzyme anode operates in commercially available beverages that contain only sugar, even without glucose.

Liquid-Phase Synthesis of Carbon Nanotubes from Alcohols

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.

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).

One-Step Liquid-Phase Synthesis of Carbon Nanotubes with Catalyst Precursors of Organometallic Complexes

This paper describes a simple, low cost one-step liquid-phase process for the synthesis of highly aligned carbon nanotube (CNT) arrays (HACNTAs). Highly pure HACNTAs were grown on a stainless steel substrate by resistance-heating in methanol solution containing one of the organometallic complex catalyst precursors, ferrocene Fe(C5H5)2 and iron pentacarbonyl Fe(CO)5. Effects of the catalyst precursors on the formation and morphologies of HACNTAs were examined. A small amount of non-aligned multi-walled CNTs (MWCNTs) were grown from 1 mM Fe(C5H5)2 methanol solution. Highly pure HACNTAs composed of MWCNTs were readily grown from 10 and 40 mM Fe(C5H5)2 methanol solutions by this one-step liquid-phase process. From the Fe(CO)5 methanol solution, HACNTAs were prepared even at a very low Fe(CO)5 concentration of 0.01 mM, which was about 1/1000 lower than that of Fe(C5H5)2. The optimal low concentration is attributed to the low decomposition temperature of Fe(CO)5.

Effects of H2O Addition on One-Step Liquid-Phase Synthesis of Highly Aligned Carbon Nanotubes

Highly aligned carbon nanotube arrays (HACNTAs) were synthesized on a stainless steel substrate from a methanol solution of Co(Ⅲ) acetylacetonate by the one-step liquid-phase synthesis, and effects of H2O addition on the HACNTA growth were examined. The growth rate was considerably accelerated, and the lifetime of the catalysts was prolonged by addition of a small amount of H2O. HACNTAs with over 400 m thickness were formed on the side surfaces of the substrate by resistance-heating for one hour. This suggests that the added H2O removes deposited amorphous carbons from the catalyst surfaces and consequently accelerates the growth rate.

One-Step Liquid-Phase Synthesis of Carbon Nanotubes: Effects of Substrate Materials on Morphology of Carbon Nanotubes

Effects of substrate materials and shapes have been investigated in the one-step liquid-phase (OS-LP) synthesis of carbon nanotubes (CNTs). Similar highly aligned multi-walled CNT (MWCNT) arrays (HACNTAs) with a height (ha) of ~30 µm were synthesized on the substrates of commercially available stainless steel and Inconel® alloy by a resistance heating method in methanol containing cobaltocene, whereas aligned MWCNT arrays (ha≈10 µm) with slightly poor alignment were formed on the titanium substrate, compared with those of the former two. On the other hand, very short, non-aligned MWCNTs with a length of ~1 µm were deposited on a silicon substrate. The different morphologies depending on the substrate materials are related with interaction between the pyrolytically-generated Co atoms and the surface oxide layers of the substrates. In addition, we have for the first time demonstrated that the OS-LP synthesis is suitable for CNT-coating onto intricately-shaped substrates like stainless steel mesh.

Synthesis of Highly Aligned Carbon Nanotubes in Liquid Phase

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.

Synthesis of highly aligned carbon nanotubes by one-step liquid-phase process: Effects of carbon sources on morphology of carbon nanotubes

This paper describes a unique and innovative synthesis technique for carbon nanotubes (CNTs) by a one-step liquid-phase process under ambient pressure. Vertically aligned multi-walled CNT arrays with a maximum height of 100 µm are prepared on stainless steel substrates, which are submerged and electrically heated in straight-chain primary alcohols with n C = 1–4 (n C: number of C atoms in the molecule) containing an appropriate amount of cobalt-based organometallic complex as a catalyst precursor. Structural isomers of butanol were also used for the synthesis to examine the effects of structural factors on the morphology of the deposited products. Notably, 2-methyl-2-propanol, which is a tertiary alcohol, produced only a small amount of low-crystallinity carbonaceous deposits, whereas vertically aligned CNTs were grown from the other isomers of butanol. These results suggest that the presence or absence of β-hydrogen in the molecular structure is a key factor for understanding the dissociation behavior of the carbon source molecules on the catalyst.

Study of electrochemical alkali insertion into carbonaceous materials

Electrochemical insertion of alkali metal (lithium or sodium) into carbon electrodes is studied in non-aqueous organic electrolytes at room temperature. The extent of insertion into carbon and its reversibility process were found to be affected by the type and particle size of the carbon materials. The possibility of designing an alkali-ion battery cell is discussed, using natural graphite, graphitized carbon black and carbon black as negative electrodes.

Effects of LiF Addition in Lithium Ion Conductor La0.56Li0.33TiO3

The compositions La0.56Li0.33TiO2.95F0.05•xLiF (x=0-025) were prepared by addition of LiF to the disordered form of the well-known Li ion conductor La0.56Li0.33TiO3. Although the total conductivities improved, there was no change in the bulk conductivity with LiF addition. No reflections due to LiF were observed in their XRD patterns, and the profiles and the chemical shifts of their 19F MAS-NMR resonances were almost the same as those of LiF. The results indicate that no substitution of F takes place, and that the added LiF acts simply as a sintering assistant agent.