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 (-CC-) insertion, some carbon atoms in graphyne are positively charged to facilitate O₂ 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 α- and β-graphyne allow O₂ penetration nearly barrierlessly, hence improving ORR efficiency. Our results imply that α- and β-graphyne systems are promising cathode materials to promote the performance of fuel cells.