Liquid-to-gas transition derived cobalt-based nitrogen-doped carbon nanosheets with hierarchically porous for oxygen reduction reaction

Here, Co@CoOx-based three-dimensional nitrogen-doped graphene-like carbon nanosheets (denoted as 3D HPN-GCNS/Co@CoOx) are fabricated by controllable grading-pyrolysis strategy, in which they show 3D fluffy and hierarchically porous nanostructure in and out-of-plane; large numbers of Co@CoOx-based nanoparticles uniformly embedded on graphene-like C nanosheets and mesoporous active edge introduce more ORR active sites. When applied for ORR, hybrids exhibit a half-wave potential (E-1/2) of 0.87 V and an onset potential (E-onset) of 0.92 V in 0.1 M KOH, comparable to that of commercial 20% Pt/C. The hybrids display better methanol tolerance and stability, with almost no change of ORR performance before and after 5000 cycles. H2O2 yield in ORR process is less than 5% and number of electron transfer is higher than 3.9. The remarkable features are mainly ascribed to synergistic enhancement effect, in which 3D fluffy and hierarchically porous nanostructure in and out-of-plane supplies large accessible specific activity area, allows species to efficiently participate in ORR and facilitates fast mass transfer; graphene-like C nanosheets with N-rich dopant promote O-2 adsorption and assure fast electron transport; large numbers of Co@CoOx-based nanoparticles introduce more ORR active sites. All the advantages synergistically enhance the ORR efficiency and make it a highly efficient ORR catalyst.