DFT simulation of edge halogenated nanosheets as an ORR catalyst in fuel cells

Abstract

Catalytic fuel cells have become increasingly attractive due to the harsh demand on fossil fuels. However, they are expensive due to the cost and scarcity of precious metals such as platinum. Recently, edge halogenated graphene- nanosheets have been discovered to be a low cost Oxygen Redn. Reaction (ORR) catalyst for alk. fuel cells. A better understanding of these ORR catalysts is needed to understand why the preferred product is water as opposed to the peroxide for undoped graphene, and how to utilize these catalysts for ORR in an acidic environment. This study uses the PBE flavor d. functional theory (DFT) with the SeqQUEST code to det. the most probable confirmations of the doped graphene after ball milling during synthesis. We calc. the binding energies of each species during the ORR, the barriers of each step of the ORR mechanism, and det. the onset potentials of the ORR for the three halogen edges: chlorine, bromine, and iodine. We found that the fully satd. edges of both zig- zag and armchair were most probable confirmations, and that the ORR intermediates bind to the zig- zag edges stronger than the to armchair edges. Our results predict that the ORR occurs on the edge of the armchair because our predicted onset potentials for armchair agree with expts. This study provides framework for future exploration of other acid tolerant 4- electron ORR catalysts.