MnxCu1−xCo2O4 used as bifunctional electrocatalyst in alkaline medium

Composite film electrodes containing mechanically mixed MnxCu1−xCo2O4 (0 ≤ x ≤ 1) particles, carbon black Vulcan XC72R and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were formed on the glassy carbon disk surface of a rotating ring-disk electrode (RRDE) and studied for the oxygen reduction and evolution reactions (ORR and OER, respectively) in 1 M KOH solution. The electrocatalytic activities for both reactions were observed to depend strongly on the Mn content in CuCo2O4. An opposite trend was observed for the apparent and intrinsic electrocatalytic activities for the ORR; the simultaneous presence of Cu and Mn was found to be detrimental to the intrinsic charge density, but beneficial to the geometric charge density with a maximum for Mn0.6Cu0.4Co2O4. The latter was characterized by the highest total number of electrons exchanged per O2 molecule, n, close to 4, greater k1 (4e− process)/k2 (2e− process) ratios, and by a unique and low Tafel slope (−41 mV dec−1). The results obtained for the OER showed that the intrinsic electrocatalytic activity is determined by the number of active sites (Co4+) electrochemically formed at the oxide surface prior to the OER, from Co3+ cations. The partial substitution of Cu by Mn in CuCo2O4 was found to decrease the OER activity.