Biomolecules-Derived Nitrogen-Doped Turbostratic Graphene Nanoscaffold Decorated with Cobalt Single Atoms for Enhanced Oxygen Evolution Reaction

The development of carbon-based first-row transition metal single-atom catalysts (SACs) for the electrochemical oxygen evolution reaction (OER) has recently gained tremendous attention. However, the synthesis of SACs mainly relies on tailored precursors and, therefore, requires extensive and time-consuming chemical reactions. Herein, we report a simple process for synthesizing a mesoporous cobalt SAC (CoN4@C-SAC) by the pyrolysis of readily available biomolecules without any template or acid–base treatments. Raman spectroscopy confirms minor structural defects in CoN4@C-SAC, exemplified by an ID/IG value as low as 0.13. Synchrotron X-ray total scattering analysis based on the atomic pair distribution function reveals a turbostratic graphene-like structure predominantly containing sp2 carbons with an enlarged interlayer spacing of 3.58 Å. X-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy confirm the uniform dispersion of Co–N4-type species on the graphene surfaces. With its unique nanostructure and high utilization efficiency of atomic Co sites, CoN4@C-SAC exhibits fairly good OER activity in 1 M KOH, demonstrated by a low overpotential of 339 mV at 10 mA/cm2 with a Tafel slope of 54 mV/dec, and a high mass activity and turnover frequency of 6726 mA/mg-Co and 1.06 s–1 at 1.65 V, respectively. Impedance analyses clarify that CoN4@C-SAC facilitates enhanced OER kinetics with lower charge transfer resistances. The catalyst manifests long-term stability for practical OER applications, as revealed by its steady performance over 3000 redox cycles and 65 h of a chronopotentiometry measurement.