Engineering Three-Dimensional (3D) Out-of-Plane Graphene Edge Sites for Highly-Selective Two-Electron Oxygen Reduction Electrocatalysis

Selective two-electron oxygen reduction reaction (ORR) offers a promising route for hydrogen peroxide synthesis. Defective sp2 carbon-based materials are attractive, low-cost electrocatalysts for this process. However, due to a wide-range of possible defect structures formed during material synthesis, identification and fabrication of precise active sites remain a challenge. Here, we report a highly-tunable graphene-based electrocatalyst, nanowire-templated three-dimensional fuzzy graphene (NT-3DFG), with excellent efficiency (~30 mV onset potential) and selectivity (93 $\pm$ 3 % H2O2) for two-electron ORR after process optimization for high densities of graphene edges. Using surface characterization and density functional theory calculations, we find that the edge sites are saturated by carbonyl (C=O) or hydrogen (C-H) groups, and that the zigzag edge sites with high coverage of carbonyl groups could lead to selective, two-electron ORR. We derive a general geometric descriptor based on the local coordination environment that provides activity predictions of graphene surface sites with ~0.1 V accuracy. Our combined synthesis and model-based approach accelerates active site characterization and carbon-based electrocatalyst discovery.