Graphynes as Promising Cathode Material of Fuel Cell: Improvement of Oxygen Reduction Efficiency

The sluggish kinetics of oxygen reduction reaction (ORR) on cathode is an invariable bottleneck in the fuel cell industry. Recently, a rising 2D carbon allotrope, graphyne with fascinating properties, appears to be a potential candidate to promote fuel cell performance. We investigated ORR process on three different graphyne models by density functional theory calculations. Because of the acetylenic linkage (-C equivalent to C-) insertion, some carbon atoms in graphyne are positively charged to facilitate O-2 dissociation. It was found that the first two-hydrogen addition produces a water molecule, and then the next two hydrogens furnish another water formation accompanied by the recovery of graphyne planarity. The ORR process on three graphyne models exhibits an efficient four-electron process. Moreover, the 18-membered rings in alpha- and beta-graphyne allow O-2 penetration nearly barrierlessly, hence improving ORR efficiency. Our results imply that alpha- and beta-graphyne systems are promising cathode materials to promote the performance of fuel cells.