Electrochemical Synthesis of Spinel Type ZnCo2O4 Electrodes for Use as Oxygen Evolution Reaction Catalysts.

A new electrochemical synthesis route was developed to prepare spinel-type ZnCo2O4 and Co3O4 as high quality thin film-type electrodes for use as electrocatalysts for oxygen evolution reaction (OER). Whereas Co3O4 contains Co(2+) in the tetrahedral sites and Co(3+) in the octahedral sites in the spinel structure, ZnCo2O4 contains only Co(3+) in the octahedral sites; Co(2+) in the tetrahedral sites is replaced by Zn(2+). Therefore, by comparing the catalytic properties of ZnCo2O4 and Co3O4 electrodes prepared with comparable surface morphologies and thicknesses, it was possible to examine whether Co(2+) in Co3O4 is catalytically active for OER. The electrocatalytic properties of ZnCo2O4 and Co3O4 for OER in both 1 M KOH (pH 13.8) and 0.1 M phosphate buffer (pH 7) solutions were investigated and compared. The results suggest that the Co(2+) in Co3O4 is not catalytically critical for OER and ZnCo2O4 can be a more economical and environmentally benign replacement for Co3O4 as an OER catalyst.