Satoshi Motoo

Electrocatalysis by ad-atoms: Part II. Enhancement of the oxidation of methanol on platinum by ruthenium ad-atoms

Summary The ad-electrode has the same electrocatalytic characteristics as the alloy electrode for the oxidation of methanol on Ru-Pt catalyst system. It is indicated that the surface atoms play predominant roles in cooperation with each other for the oxidation of methanol. This supports the bi-functional mechanism of electrocatalysis.

Electrocatalysis by ad-atoms: Part III. Enhancement of the oxidation of carbon monoxide on platinum by ruthenium ad-atoms

Summary Enhancement of carbon monoxide oxidation on platinum by ruthenium ad-atoms was found to take place in two θ Ru regions; one by the increase of ( n Pt−Ru ) av and another by the increase of ( n Ru−Ru ) av , as expected from the standpoint of the bi-functional theory proposed by the authors.

Preparation of highly dispersed Pt + Ru alloy clusters and the activity for the electrooxidation of methanol☆

A new method for the preparation of Pt + Ru binary catalyst has been developed which provides a simple way of obtaining a specific surface area (ca. 80 m2 g−1) more than 3 times larger than that obtained by conventional methods. This method is based on the co-deposition of fine oxides of platinum and ruthenium in atomic scale in a mixed salt solution of these metals followed by reduction with hydrogen bubbling. It was revealed that the binary catalyst prepared by this method forms alloy clusters of their solid solution, in which platinum atoms are replaced by ruthenium atoms on the lattice points of a face-centred cube in the region of Ru/Pt ratios less than 0.75. The supported alloy on carbon black exhibited an extremely high catalytic activity during the electrooxidation of methanol; i.e. ca. 200 mA cm−2 at 0.4 V and a limiting current of more than 1 A cm−2 when Ru/Pt = 1/1. From a comparison of the relationship between the composition of the alloy and the activity with that of an ad-electrode having ruthenium ad-atoms with a well-defined coverage, it was concluded that the composition of the alloy cluster surface is probably the same as that of the cluster bulk.

Electrocatalysis by ad-atoms

Summary The ad-electrodes Au-Pt(subs) and Au-Pd(subs) have the same electrocatalytic characteristics for methanol oxidation as the Au-Pt and Au-Pd alloy electrodes. These findings indicate the surface composition to play predominant roles in the methanol oxidation. The bi-functional theory provided and will provide useful tools for the prediction of new electrocatalysts.

Experimental analysis of the reaction layer structure in a gas diffusion electrode

Abstract The micro-structure of the reaction layer and the performance of a PTFE-bonded gas diffusion electrode having different PTFE contents have been studied experimentally using electrochemical techniques and a mercury pore sizer. A more practical image of the structure has resulted in comparison with any of the models postulated previously. Maximum performance was obtained at 30% PTFE content for oxygen reduction with ca. 75% utilization of platinum clusters, where an activation process is controlling the performance. The reaction layer consists of two distinctive pore distributions with a boundary of ca. 0.1 μm. The smaller pore (primary pore) was assigned to the space in-between the primary particles in their agglomerate and the larger one (secondary pore) to that in-between the agglomerates. Platinum clusters of ca. 80% were located in the primary pores and most of the PTFE was in the secondary pores. On the basis of the experimental results, a schematic micro-structure for the reaction layer is proposed. It was possible to determine the degree of occupation of each pore by the electrolyte or gas from the experimental results. It was revealed that the primary pore works as a reaction volume while the secondary pore works as main gas channels, e.g. 80% of the former is occupied by electrolyte and 30% of the latter contains gas at the composition of maximum performance. Increased gas channels and high utilization of platinum clusters are essential for a high-performance gas diffusion electrode. They were achieved by dispersing efficiently both the catalysed carbon black and the PTFE.

Electrochemistry of platinum single crystal surfaces: Part I. Structural change of the Pt (111) surface followed by an electrochemical method

Abstract The structural change of an atomically smooth Pt (111) surface induced by oxidation has been followed by an electrochemical method in a sulfuric acid solution. A Pt (111) surface obtained by rapid cooling by a droplet of ultra-pure water (the method of Clavilier), and that obtained by cooling in an atmosphere containing no oxygen, after annealing at high temperature, were found to give an atomically smooth, clean surface. A sample cleaned by cycles of ion bombardment and annealing for LEED observation could also give atomically smooth, clean surfaces if the sample was not exposed to a vacuum for too long and was appropriately protected against contamination from filling pure gas. Holes and Pt adatoms are produced by oxygen, in an oxygen atmosphere below 540°C and by electro-oxidation at a potential negative to 1.2 V RHE. Such a reconstructed surface returns to the original surface by heating up to 540°C in oxygen-containing atmospheres or up to 270°C in an atmosphere containing no oxygen. The latter temperatures is that of the return of Pt adatoms to their original lattice points and the former is that of the desorption of oxygen atoms from the holes followed by the return of Pt adatoms to the holes.

Arrangement of ad-atoms of various kinds on substrates: Part I. Platinum substrate

Abstract The number of platinum sites occupied by a foreign atom was determined with use of pulse technique. The foreign atoms included are Cu, Ag, Cd, Hg, In, Tl, Ge, Sn, Pb, Se, Te, As, Sb, and Bi. The approximate value is 1 for the first two, 2 for the next nine and 3 for the others. Silver and copper ad-atoms are closely packed on platinum surface, but the ad-atoms of the other elements are arranged on the surface leaving geometrical room on it even when a complete monolayer is formed.

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution

Rearrangement from disordered to ordered surface structure of copper ad-atoms on platinum takes place in the potential range from 0.2 to 0.6 V (RHE). This rearrangement makes the number of the pairs (nPt−Pt) decrease, thus resulting the decrease of the recombination of adsorbed hydrogen hence the reduction of the hydrogen evolution rate.

New preparation method of a high performance gas diffusion electrode working at 100% utilization of catalyst clusters and analysis of the reaction layer

Abstract The new preparation method of a gas diffusion electrode, based on the concept that the functions of the reaction layer in the electrode are allotted completely to a hydrophilic, catalysed carbon black and a wet-proofed carbon black, produces very high performance gas diffusion electrodes working at 100% utilization of platinum clusters in sulphuric acid and phosphoric acid. The suffer no polarization losses caused by mass transport up to a high current density on the optimized structure of the reaction layer. It was demonstrated that the performance controlling process can be easily analysed by the use of the utilization defined by us and by the change of Tafel slope with the structure change of the reaction layer.

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution: Part IV. Tin and lead ad-atoms on platinum

Abstract The state of an arsenic layer electrodeposited at various potentials on platinum electrodes has been examined electrochemically. The relation between the state and the electrocatalytic activity for hydrogen evolution has been investigated. The number of vacant sites have been found to increase with lowering of the deposition potential. The activity has been found to depend not on the amount of deposited arsenic but on the number of vacant sites. The difference in the effects of arsenic and of copper on hydrogen evolution is pointed out. This is attributed to the difference in the affinity of the ad-atoms for hydrogen.