Core@shell structured Co-CoO@NC nanoparticles supported on nitrogen doped carbon with high catalytic activity for oxygen reduction reaction.

A composite with a hierarchical structure consisting of nitrogen doped carbon nanosheets with the deposition of nitrogen doped carbon coated Co-CoO nanoparticles (Co-CoO@NC/NC) has been synthesized by a simple procedure involving the drying of the reaction mixture containing Co(NO 3 ) 2 , glucose, and urea and its subsequent calcination. The drying step is found to be necessary to obtain a sample with small and uniformly sized Co-CoO nanoparticles. The calcination temperature has a great effect on the catalytic activity of the final product. Specifically, the sample prepared at the calcination temperature of 800 °C shows better catalytic activity of the oxygen reduction reaction (ORR). Urea in the reaction mixture is crucial to obtain the sample with the uniformly sized Co-CoO nanoparticles and also plays an important role in improving the catalytic activity of the Co-CoO@NC/NC. Additionally, there exists a strong electronic interaction between the Co-CoO nanoparticles and the NC. Most interestingly, the Co-CoO@NC/NC is highly efficient for the ORR and can deliver an ORR onset potential of 0.961 V vs. RHE and a half-wave potential of 0.868 V vs. RHE. Both the onset and half-wave potentials are higher than those of most catalysts reported previously and even close to those of the commercial Pt/C (the ORR onset and half-wave potential of the Pt/C are 0.962 and 0.861 V vs. RHE, respectively). This, together with its high stability, strongly suggests that the Co-CoO@NC/NC could be used as an efficient catalyst for the ORR.