The report describes the findings of an investigation of nanoengineered gold-platinum (AuPt) catalysts in proton exchange membrane fuel cells. The membrane electrode assembly was prepared using carbon-supported AunPt100-n nanoparticles with controlled sizes and bimetallic compositions that were thermally treated under controlled temperature, atmosphere, and time. Examples shown in this report included Au22Pt78/C and Au49Pt51/C catalysts treated at 400-500 degrees C. The electrocatalytic performances of these catalysts in the fuel cells was found to be dependent on the bimetallic composition and the nanoscale phase properties which are controlled by the thermal treatment parameters (temperature and time). Excellent fuel cell performance was observed for the catalysts which are characteristic of an alloyed AuPt phase with a lattice parameter approaching that for an Pt-rich alloy phase. The results have also demonstrated excellent stability of the nanoengineered AuPt catalysts in fuel cells. The observed combination of high activity and high durability of the selected AuPt catalysts indicated that this nanoengineered bimetallic catalyst system, upon further refinement and optimization of the nanoscale phase properties and durability serve as a promising candidate of electrocatalysts for the practical application in Proton Exchange Membrane fuel cells. (C) 2010 Elsevier B.V. All rights reserved.