Mechanism of the oxygen reduction reaction from DFT calculations: Implications for improved catalysts

Abstract

In order to use d. functional theory (DFT) to seek improved catalysts for the Oxygen Redn. Reaction (ORR) in Proton Exchange Membrane fuel cells (PEMFC), we developed a systematic way to handle the barriers of electron transfer reactions [e.g. H+ + e-+ Oad e OHad] within the DFT framework. We apply this new method to detg. the optimum operating electrochem. potential for the Pt-catalyzed fuel cell and show how to est. the change in efficiency from changes in the reaction barriers. Based on our mechanism and calcd. barriers we suggest new catalysts for improved rates. Proton Exchange Membrane fuel cells (PEMFC) are most promising emission free energy systems for homes and families. However, the kinetics for the catalytic oxygen redn. reaction (ORR) 1/2 O2 + 2 H+ + 2 e e H2O remain too slow, increasing the amt. and cost of the catalyst to too high a level for widespread application. To use D. Functional Theory (DFT) to det. how the barrier would change for new alloys, a crit. issue is to account for the dependence of the electron transfer steps on the external electrochem. potential. To accomplish this we developed a systematic approach for handling the electron transfer step along with the solvation effects and including the effect of the external electrochem. potential on the electron transfer reactions involved in ORR. We applied this approach to several promising alloys to suggest new improved catalysts for ORR.