ORR and OER on Ni-modified Co3O4(111) Cathodes for Zn-Air Batteries - A Combined Surface Science and Electrochemical Model Study

The performance of structurally and chemically well‐defined Ni‐free and Ni‐modified single‐crystalline Co$_{3}$O$_{4}$(1 1 1) thin‐film electrodes in the oxygen reduction and evolution reactions (ORR and OER) was investigated in a combined surface science and electrochemistry approach. Pure and Ni‐modified Co$_{3}$O$_{4}$(1 1 1) film electrodes were prepared and characterized under ultrahigh‐vacuum conditions by scanning tunneling microscopy and X‐ray photoelectron spectroscopy. Both Ni decoration (by post‐deposition of Ni) and Ni doping (by simultaneous vapor deposition of Ni, Co, and O$_{2}$) induced distinct differences in the base cyclic voltammograms in 0.5 m KOH at potentials higher than 0.7 V compared with Co$_{3}$O$_{4}$ (1 1 1) electrodes. Also, all oxide film electrodes showed a higher overpotential for the ORR but a lower one for the OER than polycrystalline Pt. Ni modification significantly improved the ORR current densities by increasing the electrical conductivity, whereas the OER onset of approximately 1.47 V$_{RHE}$ (RHE: reversible hydrogen electrode) at 0.1 mA cm$^{-2}$ was almost unchanged.