Synthesis and Characterization of Nitrogen-Doped Ordered Mesoporous Hollow Carbon Spheres for the ORR

Abstract

This work presents the synthesis by a hydrothermal procedure of metal-free nitrogen-doped Ordered Mesoporous Hollow Carbon Spheres (N-OMHCS) starting from a SiO2 template. N-OMHCS powders have been functionalized with methanol using the intermittent microwave heating technique to produce the N-OMHCS-f sample. Then, N-OMHCS and N-OMHCS-f have been evaluated as cathode electrocatalysts for the Oxygen Reduction Reaction (ORR) in 0.5 mol L-1 KOH, with the rotating ring-disk electrode technique (RRDE). The morphology of N-OMHCS and N-OMHCS-f is that of hollow porous spherical particles of carbon of 280 nm in diameter. The chemical composition analysis shows that N-OMHCS-f is composed of basically C and O. The electrochemical results indicate that N-OMHCS-f are active for the ORR, with an onset potential of 0.81 and 0.82 V/RHE and a limiting current of -3.6 and -2.3 mA cm-2, respectively. On the other hand, both electrocatalysts produce about the same amount of H2O2 (between 14 and 26 %). Meanwhile, the number of electrons transferred at the electrocatalysts is between 3.6 and 3.8, which is close to a 4e- transfer mechanism. The catalytic activity of N-OMHCS and N-OMHCS-f can be attributed to their high specific surface area and porous structure, which provides a triple phase region promoting the adsorption-desorption of O2.