Chirality Induces the Self-Assembly To Generate a 3D Porous Spiral-like Polyhedron as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction.

Abstract

The sluggish kinetics and large overpotential of the oxygen reduction reaction (ORR) severely limit the widespread production and application of metal-air batteries. Herein, a conductive three-dimensional (3D) porous spiral-like polyhedron structure composed of nitrogen-doped carbon nanosheets (L/D-SPNC) was utilized as catalysts with combination of 3D hierarchical porous properties and distinguishing intrinsic properties of two-dimensional (2D) nanosheets for ORR. The chiral template, l/d-tartaric acid, induces the self-assembly of the supramolecule and the formation of an orderly array of carbon with spiral-like surface feature on a molecular scale. The resulting L/D-SPNC exhibits a small wall thickness (2.5 nm), large specific surface area (2034.2 m2/g), and high conductivity (155.76 S/m), which indicates that the properties of 2D nanosheets building blocks are kept in 3D mode. As catalysts for ORR, the optimized L-SPNC-950-1 exhibits a more positive onset potential of 1.03 V compared with those of Pt/C (1.00 V) and a half-wave potential of 0.87 V is also comparable to those of Pt/C (0.87 V). Al-air battery discharge data demonstrate that the spiral-like structure facilitates the diffusion of the electrolyte and oxygen on a three-phase interface, causing weak polarization. Density functional theory (DFT) calculations prove that the twisted surface aggravates the differential charge distribution between C-C/C-N bonds.