Liquid to gas transition derived cobalt based nitrogen doped carbon nanosheets with hierarchically porous for oxygen reduction reaction
Abstract 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 (E1/2) of 0.87 V and an onset potential (Eonset) 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 O2 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.