The catalytic oxygen electroreduction properties of platinum alloyed with base metals were screened using a high throughput combinatorial method. Candidate catalysts were identified by comparing the activity-stability-composition relationships between the platinum alloys and a pure platinum standard. Among the alloys studied, PtCo, PtNi, PtZn, and PtCu displayed the highest catalytic activities towards molecular oxygen electroreduction, but suffered from poor chemical stability in acid electrolytes. Alloys based on PtW, PtTi, and PtSe offered modest catalytic activity improvements and good chemical stabilities. In addition to the high throughput discovery, various synthesis technologies were studied to engineer alloy particles on the nanoscale. A good correlation in catalytic activity was found between thin film and carefully engineered powder catalysts. (c) 2006 Elsevier B.V. All rights reserved.