On the Activity of Platinum Catalysts in Solution

Abstract

The effects of thermal treatment and chemical etching of platinum on the specific rate of the chemical reaction of chemisorbed oxygen with hydrogen were determined. The hydrogen was present in electrochemically clean 1M H2SO4 and in the derma of the metal. On successive thermal treatments of bright Pt beads, which were heated to the melting point and then slowly recrystallized under high temperatures, the specific rate varied randomly from trial to trial. Where heating was more uniform, and the cooling rate slower, reaction of hydrogen with Pt-O was usually faster. Repeated aqua regia etching of a given Pt bead caused monotonic improvement until a rate between 0.014 and 0.021 amp/cm 2 was attained. Rates on Pt wire electrodes, which probably differed from the flame-formed Pt beads both in average crystallite size and in number of defects (created by the drawing process and only partially removed by subsequent annealing), were highly variable, but considerably lower than on beads. Surfaces whose activity for the Pt-O/ hydrogen reaction differed manyfold showed no differences in anodic charging curves nor did electrochemical rates of water oxidation at +0.617 and ~0.587v (NHE) or reduction of hydrogen ions at +0.300v differ. It appears that many electrochemical reactions are insensitive to these differences in surface condition. Because of its great sensitivity to catalyst pretreatments, the Pt-O/ hydrogen reaction is identified as a "demanding reaction," especially useful for identifying and examining certain variables affecting contact catalysis in solution. Since impurity sorption is one such variable, the rate of this reaction is one of the most responsive cleanliness tests available. Boudart et al. (1) have pointed out that the rates of ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74

Polarization Phenomena Relating to Physiological Electrodes

“…Further support for the role of adsorbed oxygen is given by the studies of Schuldiner and co-workers ( 1966), who have succeeded in reducing the oxygen level in a closed system to 10-10 atmospheres, pulsing the system, and then demonstrating the contribution of adsorbed oxygen to the voltage waveform (Warner & Schuldiner, 1968). Through this technique, one can hopefully associate specific chemical reactions with corresponding breaks in the voltage curves.…”

Instruments for use in electrode process research

“…Semiconductor switches are not suitable in this circuit because of their high 'on' resistance. An alternative method using diode switches has been suggested (Warner and Schuldiner 1967) and this permits rapid switching. An ingenious though somewhat more complex circuit that permits mode switching with semiconductor switches has been published by Bruckenstein and Miller (1970).…”