Masami Shibata

High Performance Catalyzed‐Reaction Layer for Medium Temperature Operating Solid Oxide Fuel Cells

New concepts for a high performance catalyzed-reaction layer for medium temperature operating solid oxide fuel cells were proposed. Mixed conducting oxide particles, samaria-doped ceria (SDC), were employed as the anode material utilizing highly dispersed noble metal catalysts on their surface. As the cathode material, Sr-doped LaMnO[sub 3] (LSM) particles catalyzed with microcrystalline Pt were employed. Performances of the anode or cathode were examined in the cell using yttria-stabilized zirconia electrolyte at a series of operating temperatures. It was found that the anodic polarization resistance and its activation energy were greatly decreased by loading only a small amount of the catalysts (such as Ru, Rh, and Pt) onto the SDC particles. The polarization loss at the anode showed a minimum value by using the SDC particles with a mean diameter of 1.5 to 2.0 [mu]m. A large depolarizing effect was also observed with a Pt-catalyzed LSM cathode, especially at high current densities.

Design of Alloy Electrocatalysts for CO 2 Reduction III . The Selective and Reversible Reduction of on Cu Alloy Electrodes

Many Cu alloys have been studied for electrocatalytic activity of reduction in aqueous solution. Anomalously low overpotentials with highly selective Cu alloy catalysts have been seen for the reduction of to, , or . Cu‐Ni alloys produce and selectively at reversible potentials and Cu‐Sn and Cu‐Pb produce and with an enhanced reaction rate at the reversible potentials of formation. Other alloy catalysts such as Cu‐Zn, Cu‐Cd, or Cu‐Ag also exhibit behaviors distinct from those of the elemental metals. The results reported here indicate further possibilities for the development of powerful new electrocatalysts for the reduction of .

High performance RuPd catalysts for CO2 reduction at gas-diffusion electrodes

Abstract The reactivity and selectivity of CO 2 reduction has been examined at gas-diffusion electrodes made of Ru, Pd and their alloy (Ru:Pd = 1:1). It was found that the current efficiency for the formation of formic acid at the gas-diffusion electrodes with RuPd catalysts is 90% at −1.1 V vs. NHE, where the current density is 80 mA.cm −2 . In addition, no CO formation was observed at gas-diffusion electrodes with RuPd catalysts.

Electrocatalysis by ad-atoms: Part XII. Enhancement of carbon monoxide oxidation on platinum electrodes by oxygen adsorbing ad-atoms

Abstract The effect of oxygen adsorbing ad-atoms on CO oxidation was examined on a Pt electrode. The activity is extremely enhanced by these ad-atoms, as predicted by the bifunctional theory on a binary electrocatalyst. The enhancement effects depend on their oxygen adsorbing property, i.e. the ad-atoms which exhibit higher equilibrium oxygen coverages at a low potential give higher enhancement effects in the order Sn > Ge (>; Pb) for the IVth group and As &>; Sb (> Bi) for the Vth group, where the Pb and Bi ad-atoms, having almost no oxygen adsorbing property, exhibit very small effects. It was revealed that the primary factor of the enhancement is the onset potential of oxygen adsorption by these ad-atoms. The secondary factor is the rate of the oxygen adsorption or that of surface reaction between the oxygen and CO adsorbed by platinum sites.

Electrocatalysis by ad-atoms: Part VI. Enhancement of CO oxidation on Pt(subs) and Pt-Au(subs) electrodes by Sn ad-atoms

Abstract The role of the surface and bulk for electrocatalysis has been examined. In order to examine whether the surface controls the kinetics of CO oxidation, a monolayer or submonolayer amount of Pt atoms were deposited on an Au electrode, and then Sn ad-atoms, which are effective for CO oxidation on a Pt electrode, were deposited on Pt-Au(subs) electrodes. It was found that a complete monolayer of Pt atoms makes the kinetics on an Au electrode the same as that on a Pt electrode, and that Sn ad-atoms enhance the kinetics of CO oxidation on the Au electrode, having a complete monolayer of Pt atoms, in the same way as they do on a Pt electrode. It is concluded that the adsorption properties of the surface is all-important in electrocatalysis for CO oxidation.

Electrocatalysis by ad-atoms: Part IX. A fast parallel path for formaldehyde oxidation on a platinum electrode by oxygen adsorbing ad-atoms

Abstract The effect of various ad-atoms on formaldehyde oxidation was examined on a Pt electrode. Ad-atom species are found to be classified into two groups according to their way of affecting the electrode reaction: one consists of Cu, Ag, Tl, Hg, Pb, As, Bi, Te and Se, the other Ge, Sn and Sb. The enhancement effect of the former depends on the number of Pt sites occupied by an ad-atom of each species (SM), which suggests to us that geometrical control of Pt site arrangement plays an important role in the enhancement. The latter group of ad-atoms adsorb oxygen atoms, and these oxygen atoms are considered to play an important role in this enhancement. The enhancement ratio by the latter group of ad-atoms is much greater than that by the former group. The enhancement by the latter group of ad-atoms is via a new rapid parallel path, which has not been found on a Pt electrode for formaldehyde oxidation.

Electrocatalysis by ad-atoms: Part XX. Rate-determining step in methanol oxidation enhanced by oxygen-adsorbing ad-atoms

Abstract Sn, Ge, As, Sb and Ru ad-atoms were experimentally verified to adsorb oxygen or oxygen-containing species. It was found that methanol oxidation is enhanced by Sn and Ru ad-atoms but not by Ge, As and Sb ad-atoms. The purpose of this work is to elucidate why oxygen donation is possible for Ru and Sn ad-atoms but not for Ge, As and Sb ad-atoms. The rates of each of the elementary steps in methanol oxidation were determined, during the transient state on Pt electrodes having oxygen-adsorbing ad-atoms, and on a Pt electrode. The reason why As and Sb ad-atoms, which adsorb oxygen in a potential region far more negative than Pt, cannot donate their oxygen atoms for the oxidation of methanol is that these ad-atoms inhibit the first step, which is the dehydration process and is the precursor to the second step, which involves oxygen acceptance.

Electrochemical synthesis of urea at gas-diffusion electrodes: Part VI. Simultaneous reduction of carbon dioxide and nitrite ions with various metallophthalocyanine catalysts

Abstract Simultaneous reduction of carbon dioxide and nitrite ions was investigated at gas-diffusion electrodes with various metallophthalocyanine (M–Pc, M: Cr, Mo, Mn, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, In, Tl, Sn and Pb) catalysts. The formation of urea, CO, formic acid and ammonia at the gas-diffusion electrodes with Group 8–14 catalysts, except for Al and Ge, was found in the simultaneous reduction. The maximum current efficiency of urea formation is about 40% at −1.5 V on Ni–Pc catalysts. The formation of urea at the gas-diffusion electrodes with Group 4–7 catalysts was not found in the simultaneous reduction of CO 2 and nitrite. The ability for urea formation with the catalysts depends on the ability for CO and NH 3 formation. The catalysts with high ability for CO and NH 3 formation could form large amounts of CO-like and ammonia-like precursors.

Design of alloy electrocatalysts for CO2 reduction: Improved energy efficiency, selectivity, and reaction rate for the CO2 electroreduction on Cu alloy electrodes

The purpose of this preliminary note is to report the significant improvement that alloying of Cu with the other metals has on the energy efficiency, selectivity, and reaction rate for the reduction of CO 2 , based on a design concept which will be described elsewhere

Structural changes at various Pt single crystal surfaces with potential cycles in acidic and alkaline solutions

Structural changes at various Pt single crystal surfaces of higher Miller index before and after many potential cycles were examined with in situ STM and cyclic voltammetry in acidic and alkaline solutions. STM images at Pt(111), Pt(100) and Pt(210) after 100 potential cycles in 0.05 M H2SO4 solution were observed. Many islands of platinum atoms on the terraces of Pt(111) and Pt(100) were found after the potential cycles, but not on Pt(210). The Pt(210) surface is changed with more difficulty with potential cycling than the Pt(111) and Pt(100) surfaces. Voltammograms for surfaces of higher Miller index after 500 potential cycles were examined. The sharp peaks of the hydrogen desorption wave become wider after the potential cycles. After the potential cycles, the shape of the voltammograms at Pt(111) and Pt(110) groups change into that at Pt(320) or Pt(530). The shapes of the voltammograms at Pt(100) groups change into that at Pt(310) after the potential cycles.