Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure.

The fuel cell is a promising alternative to environmentally unfriendly devices that are currently powered by fossil fuels. In the polymer electrolyte membrane fuel cell (PEMFC),the main fuel is hydrogen,which through its reaction with oxygen produces electricity with water as the only by-product. To make PEMFCs economically viable,there are several problems that should be solved; the main one is to find more effective catalysts than Pt for the oxygen reduction reaction (ORR),1/2 O 2 + 2H + + 2e = H2O. The design of inexpensive,stable,and catalytically active materials for the ORR will require fundamental breakthroughs,and to this end it is important to develop a fundamental understanding of the catalytic process on different materials. Herein,we describe how variations in the electronic structure determine trends in the catalytic activity of the ORR across the periodic table. We show that Pt alloys involving 3d metals are better catalysts than Pt because the electronic structure of the Pt atoms in the surface of these alloys has been modified slightly. With this understanding,we hope that electrocatalysts can begin to be designed on the basis of fundamental insight.