The anodic oxidation of ammonia in alkaline solutions was investigated by using rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. The ammonia oxidation current on the rotating platinum disk was confirmed not to increase but to decrease with increasing the rotation rate at 25-60 degrees C. The in situ ring electrode detector gave two kinds of signals for the electroactive species transported from the disk electrode engaged in ammonia oxidation; one can be again reduced and another can further be oxidized on Pt or Ni ring. These results suggested that at least some of the intermediates involved in ammonia oxidation on Pt may not be strongly adsorbed but be detached from the surface regions. (c) 2004 Elsevier Ltd. All rights reserved.