Anodische oxydation von kohlenmonoxid an platin in Schwefelsäure und phosphorsäure

In the anodic oxidation of carbon monoxide the polarization of a Raney-platinum electrode in phosphoric acid is, even at a temperature of 150°C, much larger than in dilute sulphuric acid at 90°C. In both acids the chemical conversion of carbon monoxide with water under formation of carbon dioxide and hydrogen (water-gas reaction) takes place at the platinum catalyst. In dilute sulphuric acid this reaction can be accelerated substantially by covering the platinum surface partially with sulphur. At such an electrode a reference potential of 250 mV against hydrogen is observed in 3N sulphuric acid and at a current density of 200 mA/cm². The hydrogen oxidation is not affected by the sulphur covering. Carbon monoxide and hydrogen react at the same time. Conversion of carbon monoxide takes place even in the presence of the tenfold quantity of hydrogen or carbon dioxide. The sulphur covering is stable up to a reference potential of 600 mV; at a higher polarization of the electrode the sulphur covering is oxidized to give sulphur dioxide.