Nitrogen-Doped Graphene Oxide Electrocatalysts for\nthe Oxygen Reduction Reaction

Abstract

Platinum\ngroup metal-free (PGM-free) electrocatalysts for the oxygen\nreduction reaction (ORR) often exhibit a complex functionalized graphitic\nstructure. Because of this complex structure, limited understanding\nexists about the design factors for the synthesis of high-performing\nmaterials. Graphene, a two-dimensional hexagonal structure of carbon,\nis amenable to structural and functional group modifications, making\nit an ideal analogue to study crucial properties of more complex graphitic\nmaterials utilized as electrocatalysts. In this paper, we report the\nsynthesis of active nitrogen-doped graphene oxide catalysts for the\nORR in which their activity and four-electron selectivity are enhanced\nusing simple solvent and electrochemical treatments. The solvents,\nchosen based on Hansen’s solubility parameters, drive a substantial\nchange in the morphology of the functionalized graphene materials\nby (i) forming microporous holes in the graphitic sheets that lead\nto edge defects and (ii) inducing 3D structure in the graphitic sheets\nthat promotes ORR. Additionally, the cycling of these catalysts has\nhighlighted the multiplicity of the active sites, with different durability,\nleading to a highly selective catalyst over time, with a minimal loss\nin performance. High ORR activity was demonstrated in an alkaline\nelectrolyte with an onset potential of ∼1.1 V and half-wave\npotential of 0.84 V vs RHE. Furthermore, long-term stability potential\ncycling showed minimal loss in half-wave potential (<3%) in both\nN₂- and O₂-saturated solutions with improved\nselectivity toward the four-electron reduction after 10000 cycles.\nThe results described in this work provide additional understanding\nabout graphitic electrocatalysts in alkaline media that may be utilized\nto further enhance the performance of PGM-free ORR electrocatalysts.