Electrocatalysis of Oxygen on Bifunctional Nickel-Cobaltite Spinel

Transition-metal-based materials are among the most active and durable catalysts for the effective electrocatalysis of oxygen-related reactions. Herein, we present a study on bifunctional catalysts as air electrodes aimed at metal-air batteries based on nickel and cobalt spinel (NiCo2O4) supported on electrospun carbon nanofibers. The physicochemical features of these transition-metal-based catalysts are essential for the understanding of their electrochemical activity. Results show that the major presence of oxidized Ni and Co species (Ni3+ and Co3+) produces higher activity for the oxygen evolution reaction (OER), whereas lower oxidation states of the metals (Ni2+, Co2+, Ni-0 and Co-0) together with the presence of N-doped carbon lead to enhanced oxygen reduction reaction (ORR) performance. This study highlights the importance of designing catalysts in terms of crystallographic structure and proper oxidation states of the elements for maximizing their performance.