EFFECTS OF OXIDIZABLE ANION ADSORPTION ON THE ANODIC BEHAVIOR OF PLATINUM.
Interim rept. (Phase 1),
NAVAL RESEARCH LAB WASHINGTON D C
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The retardation of the hydrogen oxidation reaction, which commences at about 0.7 v NHE in sulfuric acid solution, can be modified by the presence of formate ions. Steady-state, potentiostatic measurements were made in formic acid solution and formic acid-sulfuric acid solution, both in the presence and absence of hydrogen. The work showed that at potentials under 1.5 v passivity was due to adsorbed anions rather than adsorbed oxygen atoms, Pt oxides, or free radicals formed by the oxidation of water. Pure formic acid solutions were not passivated below 1.5 v however, formate ions did retard hydrogen oxidation but not as strongly as sulfate ions. The oxidation of formic acid in solutions containing sulfuric acid was affected by adsorption of both sulfate and formate ions. The retardation of the net oxidation of hydrogen and formic acid in formic acid-sulfuric acid mixtures was less than that of hydrogen in sulfuric acid. In the presence of dermasorbed oxygen, both formate and sulfate ions strongly retard the oxidation of added species. The effect of potential on reaction rate appears to depend on the particular organic species adsorbed and may reflect the potential of zero charge. Author
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