On the Activity of Platinum Catalysts in Solution. Part I. Effects of Thermal Treatment and Chemical Etching on the Pt-O/Hydrogen Specific Reaction Rate

摘要

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/sq cm was attained. Rates on Pt wire electrodes, which probably differed from the flame-formed Pt beads both in average crystallite size and 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. Electrochemical rates of water oxidation at +0.617 v and +0.587 v (NHE) and reduction of hydrogen ions at +0.300 v also did not differ. It appears that many electrochemical reactions are insensitive to these differences in surface condition. (Author)