Intrinsic Catalytic Activity of Graphene Defects for the CoII/III (bpy) 3 Dye-Sensitized Solar Cell Redox Mediator

We demonstrate that functionalized graphene, rich with lattice defects but lean with oxygen sites, catalyzes the reduction of Co^III(bpy)₃ as well as platinum does, exhibiting a rate of heterogeneous electron transfer, k₀, of ∼6 × 10^–3 cm/s. We show this rate to be an order of magnitude higher than on oxygen-site-rich graphene oxide, and over 2 orders of magnitude higher than on the basal plane of graphite (as a surrogate for pristine graphene). Furthermore, dye-sensitized solar cells using defect-rich graphene monolayers perform similarly to those using platinum nanoparticles as the catalyst.