Substituent effects of symmetric cobalt porphyrins using graphene oxide as substrate on catalytic oxygen reduction reactions

Abstract

Three symmetric cobalt porphyrins with different electron-donating substituents benzyl, triphenylamine-carbazole and carbazole at their meso-positions, nominated as Bz-CoPor，Cb-CoPor and TPACb-CoPor, respectively, were selected to dope onto graphene oxide (GO) as the electrocatalysts to check the substituent effects on oxygen reduction reaction (ORR). The spectroscopic characterization of the composites suggests there is strong electronic coupling between porphyrin and GO. The substituent effects of porphyrins on ORR are examined using a series of electrochemical measurements, suggesting that the reduction potential, diffusion-limited current density and the electron transfer number as well as the H2O2 generation yield can be strongly influenced by the porphyrin structure in acidic medium. Rotating ring-disk electrode (RRDE) tests suggest that TPACb-CoPor/GO exhibits the largest electron transfer number of 3.8 with the lowest H2O2 generation yield of 9% within the three porphyrin/GO models. Our findings suggest that the substituent effects of porphyrins on ORR can still function at the π-π interaction interfaces, and these symmetric cobalt porphyrins can undergo nearly 4-electron transfer path upon using GO as the substrate.