Tsuyoshi Hyakutake

Direct visualization of oxygen distribution in operating fuel cells.

Fuel cells are devices that produce electric power by means of the chemical reaction of oxygen and fuels more efficiently than current technologies, and they are expected to become a cleaner source of energy. Despite considerable recent advances, especially in polymer electrolyte membrane fuel cells (PEMFCs), existing technology still has drawbacks, including kinetic limitations on the oxygen reduction reaction and the instability of Pt catalysts and polymer membranes nearby, in particular during startup–shutdown cycles. The chemical reactions are uneven throughout the reaction field and not well understood. A central issue in fuel cell research is the measurement of the parameters that determine performance during cell operation, a difficult task owing to the structure of these devices. The distribution of liquid water in operating fuel cells has been measured and imaged through neutron radiography, by NMR spectroscopy, and by X-ray microtomography, and temperatures have been recorded with a thermograph. Hydrogen cross-over from the anode to cathode has been studied by mass spectrometry and magnetic resonance imaging in an operating PEMFC. Oxygen consumption and H2O2 formation, as well as the local catalytic activity of a catalyst have been investigated and visualized in solution with a scanning electrochemical microscope. However, to improve the performance and durability of PEMFCs, it is crucial to understand distributions in real time not only of liquid water but also of reactants and products (oxygen, fuel, CO2, water vapor, etc.) throughout the cell. Here we present a laboratoryuse, nondestructive system for visualizing oxygen distribution in the interior of the operating fuel cells which relies on dye films painted on the transparent gas flow field. Oxygen partial pressures were successfully visualized with spatial and time resolutions of 300 mm and 500 ms, respectively. We found that the oxygen distribution in PEMFC is not in accordance with that expected based on the current, which suggests a significant contribution from water. This imaging system is applicable to other important parameters such as water, carbon monoxide, and temperature, and should help in the design of new fuel cell separators and a reaction field called a membrane-electrode assembly (MEA). An oxygen-sensitive porphyrin, tetrakis(pentafluorophenyl)porphyrinatoplatinum (PtTFPP), was used in the visualization system. This dye complex was dispersed in an oxygenpermeable polymer matrix, poly(1-trimethylsilyl-1-propyne) (pTMSP), for making a thin, water-insoluble dye film. To understand the properties of the dye film, we placed the film in an environment with controlled oxygen partial pressure (mixtures of oxygen, nitrogen, and water vapor at 0–26 kPa of a total of approximately 101.3 kPa), temperature, and humidity, and irradiated it with a laser light at a wavelength of 407 nm. The emission from the film was filtered (> 600 nm), and the intensity was measured with a charge-coupled device (CCD) camera. Figure 1a shows a Stern–Volmer plot of the

Dual-mode oxygen-sensing based on oxygen-adduct formation at cobaltporphyrin–polymer and luminescence quenching of pyrene: an optical oxygen sensor for a practical atmospheric pressure

A dual-mode and a non-Stern–Volmer type oxygen pressure-sensitive coating was prepared by combining the cobaltporphyrin (CoP) ligated with a polymer and 1-pyrenebutyric acid (Py): the combination of the rapid and reversible oxygen (O2)-adduct formation of the CoP was accompanied by a visible absorption spectral change and luminescence quenching of Py with oxygen. The oxygen sensor composed of CoP/Py was successfully characterized by a significantly high oxygen sensitivity under the practical atmospheric oxygen pressure of 10–21 kPa. Py was adsorbed on an anodized aluminium substrate. Its luminescence decreased by quenching with oxygen which obeyed the conventional Stern–Volmer equation. Copolymers of vinylidenechloride with 1-vinylimidazole, 1-vinyl-2-methylimidazole, and 4-vinylpyridine (1, 2 and 3, respectively) were prepared to provide both an oxygen-barrier coating for the first luminescent Py layer and CoP ligation for tuning the oxygen-adduct formation equilibrium. The luminescent Py layer was further coated with a second polymer layer: The oxygen-barrier polymer coating enhanced the Stern–Volmer type luminescence intensity from the Py layer. Visible absorption of the CoP-containing polymer second layer increased in response to the oxygen-adduct formation or oxygen partial pressure, which overlapped and reduced the luminescence from the Py layer. The sum of the luminescence decreased along with an increase in the oxygen partial pressure, yielding a non-Stern–Volmer type response or high sensitivity to the oxygen partial pressure.

In situ and real-time visualisation of oxygen distribution in DMFC using a porphyrin dye compound

A luminescent porphyrin dye film has been coated onto a transparent separator on the cathode side of a direct methanol fuel cell (DMFC) to visualise clearly oxygen distribution under operating conditions by analysing emission from the dye.

Capsulation of carbon nanotubes on top of colloidally templated and electropolymerized polythiophene arrays

We describe the capsulation of colloidally templated polythiophene (P3-TAA) arrays with multi-walled carbon nanotubes (MWNTs) after colloidal template electropolymerization. The dissolution of the polystyrene (PS) particle templates, which were assembled via the Langmuir-Blodgett (LB)-like technique, allowed the formation of hollow-shell Janus type arrays.

Colorimetric Ion Sensors Based on Polystyrenes Bearing Side Chain Triazole and Donor–Acceptor Chromophores

Side chain clicked polystyrene derivatives formed by the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction showed colorimetric ion sensing behaviors when donor-acceptor chromophores, prepared by a [2+2] cylcoladdition-retroelectrocyclization between electron-rich alkynes and tetracyanoethylene (TCNE)/7,7,8,8-tetracyanoquinodimethane (TCNQ), were attached to the triazole rings. The metal ion sensing behaviors could be explained according to the theory of hard and soft acids and bases (HSAB). Hard acidic metal ions were mainly recognized by the hard basic anilino-nitrogen moieties, resulting in a decrease in the charge-transfer (CT) bands. In contrast, soft acidic metal ions led to a bathochromic shift in the CT bands due to the selective interactions with the soft basic cyano-nitrogen atoms. With the triazole spacers, more soft (and/or borderline) metal ions were recognized by the donor-acceptor chromophores probably due to more space for the various sized metal ions. The chemodocimetric anion sensing behaviors of the clicked polystyrenes were almost the same as those of the counter polystyrenes without the triazole spacers. Overall, the triazoles in this study do not serve as colorimetric sensor units towards both metal ions and anions, but they are effective spacers between the polymer main chain and ion sensing donor-acceptor side chain chromophores.

Unravelling the nature, evolution and spatial gradients of active species and active sites in the catalyst bed of unpromoted and K/Ba-promoted Cu/Al2O3 during CO2 capture-reduction

CO2 capture-reduction (CCR) is a recently developed catalytic process that combines two critical functions of the CO2 utilization path in one process, namely CO2 capture and subsequent transformation (e.g. reduction by H2) into chemical fuels or intermediates such as CO. A bifunctional catalyst material is needed and the two functions are activated by means of an isothermal unsteady-state operation (i.e. gas switching). This work employs operando space- and time-resolved DRIFTS, XAFS, and XRD to elucidate the nature and functions of Cu and the promoters. Both unpromoted and K/Ba-promoted Cu/Al2O3 catalysts were studied to illuminate the active surface species varying along the catalyst bed. The K promoter was found to uniquely facilitate efficient CO2 capture in the form of surface formates, dispersion of active metallic Cu and suppression of surface Cu oxidation. The CO2-trapping efficiency of the K-promoted catalyst is so high that CO2 capture takes place gradually along the catalyst bed towards the reactor outlet, hence creating large spatial and temporal gradients of surface chemical species. Understanding these features is of central importance to design efficient CCR catalysts. Furthermore, a completely different path for CO2 reduction was evidenced for the unpromoted and Ba-promoted Cu catalysts where CO2 can directly react with metallic Cu and oxidize its outer surface and thus releasing CO. These results also provide important new mechanistic insights into the widely investigated reverse water–gas shift reaction and the role that K and Ba promoters play.