title: A significant improvement in the electrocatalytic stability of N-doped graphene nanosheets used as a counter electrode for [Co(bpy)3](3+/2+) based porphyrin-sensitized solar cells.
abstract: A significant improvement in efficiency is achieved for porphyrin (YD2-o-C8) based dye-sensitized solar cells, coupled with [Co(bpy)3](3+/2+) mediator electrolyte. However, the poison of the counter electrode (CE) by the [Co(bpy)3](3+/2+) mediator remains a significant barrier to producing a reliable high-performance device. In this paper, nitrogen-doped graphene nanosheets (NG) are produced using a low-cost solution-based process and are used as the CE for [Co(bpy)3](3+/2+) based porphyrin-sensitized solar cells. These produce significantly better electrocatalytic activity than the commonly used Pt CE. The superior performance is a result of the increased number of catalytic sites and the wettable surface that is caused by the substitution of pyridinic and pyrrolic N into the carbon-conjugated lattice. To the authors' best knowledge, the significantly improved cycling stability (>1000 times) of NG CE for [Co(bpy)3](3+/2+) redox complexes is demonstrated for the first time.
authors.affiliation: Department of Mechanical Engineering, The University of Hong Kong , Pokfulam 852, Hong Kong.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhai
authors.forename: Chih-Chi
authors.initials: CC
authors.lastname: Lee
authors.forename: Ya-Huei
authors.initials: YH
authors.lastname: Chang
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.forename: Tzu-Chien
authors.initials: TC
authors.lastname: Wei
authors.forename: Shien-Ping
authors.initials: SP
authors.lastname: Feng
keywords: N-doped graphene; cobalt mediator; electrocatalytic reliability; porphyrin-sensitized solar cells; surface wettability