It was found that during the electrochemical reduction of molecular oxygen in acidic medium the ternary cluster materials (M(x)Mo(6)S(8); M : Ag, Ba, Cd, Zn, Sn, Pb, In) produce 4% H2O2 and the Pd-containing cluster material produces 8% H2O2 when their surface is free from oxides. Since, eg, Ag metal produces H2O2 with 60% efficiency this result proves that the multi-electron charge transfer is carried out mainly via the Mo-6-cluster which functions as the reaction centre. Hydrogen peroxide production is enhanced parallel with the oxidation of the cluster material surface. This process enriches the supported cluster electrode in oxides originating from the cluster matrix itself and from the metal excalated from the material. This phenomenon of oxidative stimulation of H2O2 generation was shown with an in situ X-ray probe.