Recent Developments in the Electrocatalysis of the O Reduction Reaction - Fuel Cell Catalysis: A Surface Science Approach - page 268

& CHAPTER 9

Recent Developments in the
Electrocatalysis of the O 2
Reduction Reaction

YE XU
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

MINHUA SHAO
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA

MANOS MAVRIKAKIS
Department of Chemical and Biological Engineering, University of Wisconsin - Madison, Madison,
WI 53705, USA

RADOSLAV R. ADZIC
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA

9.1 NEW INSIGHTS INTO THE OXYGEN REDUCTION REACTION
FROM EXPERIMENT AND THEORY

The oxygen reduction reaction (ORR) is the primary electrochemical reaction
occurring at the cathode of fuel cells, and is central to this promising technology
for efficient and clean energy generation. In low temperature proton exchange mem-
brane fuel cells (PEMFCs), the ORR is traditionally catalyzed by platinum because it
has the highest activity of the elemental metals. A multi-electron reaction, the ORR
appears to occur in two pathways (represented in acidic electrolytes):

(i) A “direct” four-electron pathway, wherein four electrons are transferred

in concert:

O 2 þ 4H þ þ 4e ! 2H 2 O