The metal effect of the inner electrode used for the decomposition of methane and the resulting evolution of hydrogen by discharge plasmas was investigated. Several different electrodes were used in this study including noble metals such as palladium and other metals such as iron and copper. The noble metals showed the highest activity in methane decomposition and hydrogen production. Nickel and gold showed considerable deactivation, whereas the activity of iron decreased less. Coated electrodes with copper and tin oxide nanoparticles exhibited high activity in these reactions. The effect of the flow rate and the cleaning of the electrode were examined as further objectives of this study. The decomposition of methane and the evolution of hydrogen decreased with increasing flow rate in a negative exponential manner due to the lower residence time. The cleaning of the electrode has a profound effect on the conversions and allows one to observe the catalytic effect of the metal electrodes, which are otherwise covered by coke produced in the reaction. A mechanism was developed using data obtained from mass spectrometry and combined gas chromatography and mass spectrometry. (C) 2003 Elsevier B.V. All rights reserved.