Surface Structure Dependent Electrocatalytic Activity of Co3O4 Anchored on Graphene Sheets toward Oxygen Reduction Reaction

Junwu Xiao,Shihe Yang,Lin Guo,Qin Kuang,Fei Xiao,Shuai Wang

doi:10.1038/srep02300

Abstract

Catalytic activity is primarily a surface phenomenon, however, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co3O4 nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co2+ ions, whereas the surface Co3+ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts.

Highlights

Catalytic activity is primarily a surface phenomenon, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity
We report a controllable synthesis of Co3O4 nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity
There is a need to systematically study the catalytic activity as a function of nanocrystalline morphology other than the size since the surface structure is tunable by varying the morphology

Summary

Introduction

Catalytic activity is primarily a surface phenomenon, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Results show that the catalytically active sites for ORR should be the surface Co21 ions, whereas the surface Co31 ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites These results underscore the importance of morphological control in the design of highly efficient ORR catalysts. No study has been reported on the correlation between the shape and the ORR catalytic activities of Co3O4 nanocrystals Such a study requires anchoring the Co3O4 nanocrystals onto a substrate, which is preferably conductive and can enhance the ORR activity and stabilize the catalyst system. As a relatively new class of carbon-based nanomaterials, graphene and carbon nanotube (CNT) have high electrical conductivity, large surface area, high mechanical strength, and structural flexibility, making them ideal substrates for supporting such nanocrystal catalysts. Shape-controllable synthesis of Co3O4 nanocrystals on graphene and CNT as composites is still an unmet challenge

Methods

Results

Conclusion