Characterization of local electrocatalytical activity of nanosheet-structured ZnCo2O4/carbon nanotubes composite for oxygen reduction reaction with scanning electrochemical microscopy

A novel nanosheet-structured ZnCo2O4/carbon nanotubes (i.e., ZnCo2O4 nanosheets/carbon nanotubes (ZnCo2O4 NSs/CNTs)) composite is successfully synthesized. Its catalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolyte is evaluated by both cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The CV results demonstrate that the ZnCo2O4 NSs/CNTs composite has good ORR catalytic activity, which is better than those of ZnCo2O4, CNTs, physically mixed ZnCo2O4 and CNTs, and Co3O4 NSs/CNTs. It could attribute to the unique ultrathin nanosheet structure and the synergetic effects of ZnCo2O4 and CNTs. Through recording the ORR currents using a microelectrode above the catalyst sample surfaces with applying different sample potentials, the differences in the local catalytic activities of these catalysts are simultaneously investigated and visualized by SECM. The obtained SECM results agree well with the CV results and also as important complements to the CV measurements. Our work proves the good ORR catalytic performance of the nanosheet-structured ZnCo2O4 /CNTs composite and introduces the SECM technique as a rapid screening method for predicting the ORR catalytic performances of the mixed transition metal oxides hybrids with providing both qualitative and quantitative local catalytic activity information.