A series of prototype direct methanol fuel cells (DMFCs) were constructed and operated under identical procedures and conditions except for the surface compositions of the anode electrocatalysts. The cathode electrocatalyst was Pt black (loading 2 mg/cm(2), specific surface area: ca. 27 m(2)/g), the electrolyte membrane was Nation(TM) 117, and the anode electrocatalysts were a series of Pt-Ru adatom (Pt-Ru-ad) nanoparticles (loading 2 mg/cm(2), specific surface area: ca. 27 m2/g) prepared by a direct surface reductive deposition of Ru-ad onto Pt black. The optimum surface coverage of Pt by Ruad was ca. 33% for DMFCs operating at 60degreesC. The optimum ranged from ca. 30 to 60% at 90degreesC. A DMFC using Pt-Ruad nanoparticles supported on carbon (Vulcan XC-72(TM)) as anode electrocatalyst was operated for 20 days at 8 h each day without loss of activity. These results, combined with those from an in situ cyclic voltammetry study, indicate that no significant Ruad dissolution and/or redistribution occurred during fabrication and operation of the prototype DMFCs. (C) 2004 Elsevier B.V. All rights reserved.