Reduction of Surface Oxide of Platinum and Gold Electrodes in Aqueous Sulfuric Acid-Local Cell Mechanism and Reactive Species

Abstract

The surface oxides of platinum and gold electrode formed anodically are gradually reduced when held at open circuit in aqueous sulfuric acid. The nature of this reaction was studied by the aid of mainly chronopotentiometric technique. It was confirmed that, for both platinum and gold, the reaction proceeds through the galvanic cell mechanism in which the bare surface of metals act as the anode electrode which oxidizes certain contaminants and the oxide covered surface act as the cathode. From the measurements of short circuited galvanic cell composed of oxidized platinum (or gold) in purified 1 N H₂SO₄ and reduced platinum (gold) in “contaminant” containing 1 N H₂SO₄, it was concluded that formaldehyde used as the contaminant was effective to platinum oxide but not to gold oxide. Both chloride and bromide as the contaminant behave oppositely, being effective to gold but not to platinum. This sort of apparently peculiar behavior of several “contaminants” has been explained by the fact that compounds which are effective as a depolarizer were those oxidized anodically on the oxide free surface of metals.