Effect of Dimensionality and Doping in Quasi-"One-Dimensional (1-D)" Nitrogen-Doped Graphene Nanoribbons on the Oxygen Reduction Reaction.

Abstract

Designing an efficient metal-free electrocatalyst for the oxygen reduction reaction (ORR) is a challenging research theme having enormous practical importance in several renewable energy technologies like fuel cell and metal-air batteries. Here we discuss a cost-effective and commercially viable strategy to develop high-performance nitrogen-doped graphene nanoribbon (N-GNR), which is a quasi-"one-dimensional" analogue of graphene. We have selected the N-GNR system to identify the doping-induced variation in the distribution of active catalytic sites experimentally in graphene-based electrocatalysts. N-GNR exhibits a comparable exchange current density (1.65 × 10-9 vs 2.25 × 10-9 A cm-2), thermodynamic potential (0.80 vs 0.83 V), and smaller Tafel slope (55 vs 60 mV dec-1) with respect to the benchmarking platinum/carbon (Pt/C), and also, more precisely, it goes through a four-electron pathway with low hydrogen peroxide yield. Although the exact mechanism is still not clear, the theme of the work is based on the identification of the possible active sites with the help of experimental evidence like X-ray photoelectron spectroscopy. These results support the assumption that an edge N (pyridinic N)-bonded adjacent C lowers the activation energy barriers of O2 adsorption, predominantly to kinetically facilitate the ORR activity. We hope these results will be helpful in developing more efficient ORR catalysts.