Katsunori Nishimura

Electrocatalytic properties of ultrafine platinum particles for oxidation of methanol and formic acid in aqueous solutions

Abstract The effect of particle size of ultrafine platinum particles, which were prepared by vacuum evaporation onto a glassy carbon rod, on the electrochemical oxidation of methanol and formic acid has been examined by a cyclic voltammetry. The specific activity for the oxidation of methanol decreased by decreasing the platinum particle size, whereas that of the formic acid increased as the particle size decreased. Features of the cyclic voltammograms of the latter reaction suggested that the ratio of the exposed Pt(100) plane of platinum particles increased with decreasing the platinum particle size, while that of Pt(110) decreased.

Electrooxidation of formate and formaldehyde on electrodes of alloys between Pd and Group IB metals in alkaline media: Part II. The possibility of complete oxidation of formaldehyde in weak alkali

The possibility of complete electrooxidation of formaldehyde on Pd + IB alloy electrodes was studied in K2CO3 solution. Formaldehyde is oxidized first to formate and hydrogen intermediate, and the latter is oxidized simultaneously on the electrodes provided that their Pd content is more than ~ 20 at.%. The rates of individual oxidation of HCOO− and HCHO become roughly equal to each other at a bulk Pd content of 50–60, 20–30 and 0–10 at.% for Pd + Cu, Pd + Ag and Pd + Au alloys, respectively. The oxidation of formate is, however, strongly retarded by the presence of formaldehyde. This retardation is least serious on Pd + Au alloy electrodes with 40–70 at % Pd, and thus they exhibit the highest electrocatalytic activity among Pd + IB alloys towards the oxidation of HCOO− to carbonate in HCOO− + HCHO mixed solution.

On-line mass spectroscopy applied to electroreduction of nitrite and nitrate ions at porous Pt electrode in sulfuric acid solutions

Abstract On-line mass spectroscopy was applied to detect volatile products of the electroreduction of NO−2 and NO−3 at Pt in 0.5M H2SO4. It provided important information, particularly on the transient behavior. Nitrite is reduced stepwise to NO (at 0.6–1 V, rhe), N2O (0.2–0.8 V) and N2 (0.1–0.6 V) in the potential ranges indicated. On the other hand, nitrate reduction takes place at much lower potentials (E

Electrocatalysis on Pd + Au alloy electrodes: Part III. IR spectroscopic studies on the surface species derived from CO and CH3OH in NaOH solution

IR spectroscopic observation has revealed that a bridge-type CO species is formed on Pd + Au alloy electrodes as well as on Pd upon chemisorption of methanol in alkaline solution. The CO species acts as a self-poisoning species for the electro-oxidation of CH3OH. The nature of the CO species is similar to that adsorbed directly from a CO-saturated solution, namely, (i) a bridged, but not linear-type CO species is formed and (ii) its amount decreases with increasing Au content. The CO species is oxidized at lower potentials on electrodes of intermediate alloy composition (40–50 at.% Pd) than on Pd. The activity of those alloys towards the electro-oxidation of CH3OH has a maximum in the same composition range. Possible schemes of formation of the bridge-type CO from CH3OH are proposed.

Electrocatalysis of Pd + Au alloy electrodes: Part IV. IR spectroscopic studies on the surface species derived from formaldehyde and formate in alkaline solutions

Abstract The formation of a bridge-type adsorbed CO species during the electro-oxidation of formaldehyde on Pd+Au alloy electrodes, but not on a Au electrode, in alkaline media was investigated by means of infrared reflectance spectroscopy. The CO species is probably formed from HCHO which is predominant in the solution at lower pH, but not from HOCH 2 O − . The species acts as a catalytic poison in formaldehyde electro-oxidation, but the effect is weaker at higher pH where oxidation of HOCH 2 O − takes place more readily. The rate of CO formation is faster at lower pH and on electrodes of higher Pd content. No CO species was detected in the HCOO − system. In mixed solutions of HCOO − and HCHO, the oxidation of formate on both Pd and Pd+Au alloy electrodes is suppressed greatly by the CO species originating from HCHO. The poisoning effect becomes less pronounced on the alloy electrodes of higher Au content.

Electrocatalytic properties of ultrafine gold particles towards oxidation of acetaldehyde and ethanol

Abstract The structural and electrocatalytic properties of ultrafine gold particles deposited onto a flat glassy carbon support (Au/GC) were investigated by means of high-resolution scanning electron microscopy (SEM) and cyclic voltammetry (CV). Gold particles of the Au/GC electrodes prepared had a hemispherical shape and were 1–12 nm in diameter. The mean particle size d decreased with decreasing amount of gold deposited M . In alkaline solutions, these electrodes oxidized acetaldehyde and ethanol anodically at the surface, when covered incompletely with the gold oxide layer. Their electrocatalytic activities per real surface area S Au increased with increasing M , or d so as to exceed those of a gold wire electrode.

Electrooxidation of formate and formaldehyde on electrodes of alloys between Pd and Group IB metals in alkaline media: Part I. Electrocatalytic properties of component metals

The electrocatalysis of alloys between Pd and Group IB metals (Pd + IB alloys) towards the oxidation of formate and formaldehyde in 1.0M NaOH has been investigated. Pd + IB alloy electrodes exhibit roughly an additivity character with respect to the component metals in their electrocatalytic activity. Pd-rich alloy electrodes are highly active towards oxidation of formate, while those rich in Group IB metals, especially Au and Cu, are active towards formaldehyde. Hydrogen gas is liberated from Group IB metals during the oxidation of formaldehyde even at potentials positive to the RHE, but it is oxidized simultaneously on the Pd+IB alloy electrodes with a bulk Pd content of more than 70 at.% for Pd + Cu or 50 for both Pd + Ag and Pd + Au. A moderate synergistic effect is seen with a maximum activity at 50 to 70 and 20 at.% Pd in the oxidation of formate on Pd+Au alloys and in the oxidation of formaldehyde on Pd + Cu alloys, respectively. The higher the electrocatalytic activity, the lower is the activation energy, but the effect is compensated partly by an accompanying decrease of the pre-exponential factor. The compensation is more extensive in the oxidation of HCHO.

Surface composition of binary alloys between Pd and Group IB metals as studied by Auger electron spectroscopy and cyclic voltammetry

The surface composition of alloys between Pd and Group IB metals (Pd+IB alloys) was investigated on the basis of Auger electron spectroscopy (AES) and cyclic voltammetry. A correction factor for the extinction of Auger peak intensities by surface contaminants, mainly carbon, in deducing the surface composition was determined first. The applicability of this method was substantiated in the case of Pd + Au alloys by the empirical rule in the electrochemical observation that the potential of the oxygen reduction peak in the voltammograms varies linearly with the surface composition. Both AES and electrochemical analysis revealed that in Pd + Au alloy specimens treated by electrochemical oxidation-reduction cycles in 0.1 M NaOH within the potential range 0.05–1.50 V (vs. RHE) the original surface composition was maintained whereas a significant amount of surface Au enrichment took place on those specimens which were anodically polarized in 0.5 M H2SO4. AES analyses of the Pd+Ag and Pd+Cu alloy systems revealed that a weak degree (less than 0.1 in atomic fraction) of surface enrichment in Ag and Cu took place when they were treated by oxidation-reduction cycles in the potential ranges 0.05–1.0 and 0.05–0.50 V (vs. RHE), respectively, in 1.0 M NaOH.

Competitive oxidation of formaldehyde and formate on amorphous copper-palladium-zirconium alloy electrodes in alkaline media

Raney-type Cu−Pd alloy electrodes were prepared from amorphous Cu−Pd−Zr ternary alloys by treatment with aq. HF, and competitive anodic oxidation reactions of HCHO and HCOO− were studied on these electrodes in alkaline media. The initial HCHO oxidation product was HCOO− even on Pd or Pd-rich alloy electrodes which should be more active to the HCOO− oxidation than to HCHO. The product HCOO− was oxidized only after a large decrease of the HCHO concentration in the electrolyte. The oxidation rate of HCOO− was considerably lowered by the existence of even a small amount of HCHO, as well as by the introduction of CO. These results suggest that the HCHO electro-oxidation is accompanied by production of a surface contaminant such as adsorbed CO. The optimum nominal Pd atomic fraction in the Cu−Pd alloy electrodes suitable for the steady simultaneous oxidation of HCHO and HCOO− in mixed solution was shown to be 0.25 and 0.4 in 1.0 M NaOH (M=moldm−3) and 0.5 M K2CO3, respectively.

Amorphous Copper‐Palladium‐Zirconium Ternary Alloys for Formaldehyde Oxidation Anode Materials

The electro-oxidation of HCHO and HCOO/sup -/ on a series of amorphous Cu-Pd-Zr ternary alloys after surface treatments with aq. HF has been investigated in 1.0M NaOH and 0.5M Na/sub 2/CO/sub 3/ at 303 K, together with surface area measurements and XPS observations. The acid treatment led to the formation of a Raney-type porous Cu-Pd alloy layer on the surface after the Zr was leached out. The surface analyses indicated a minor degree of enrichment in Pd or Cu, before or after the acid treatment, respectively. The alloy electrodes with the bulk composition of Cu:Pd = 1:3 showed the same activity of 1.2 X 10/sup -4/ A cm/sup -2/ (true) at 0.30 V (RHE) for the HCHO and HCOO/sup -/ electro-oxidation in 1.0M NaOH. The composition of 2:1 exhibited similar behaviour with the activity of 2.0 X 10/sup -5/ A cm/sup -2/ (true) in 0.5M Na/sub 2/CO/sub 3/.