Exploring oxygen electrocatalytic activity and pseudocapacitive behavior of Co₃O₄ nanoplates in alkaline solutions

Abstract

Cobalt-based materials are regarded as important materials for oxygen reduction and evolution reactions (ORR and OER) in metal-air batteries and supercapacitors. However, the activity of oxygen electrocatalysis and the pseudocapacitive performance of cobalt oxide (Co3O4) in the reported works are usually inconsistent. To explore this issue, a series of Co3O4 nanoplates are fabricated using different calcination temperatures, and their morphologies, microstructures, and electrochemical behaviors in alkaline solutions are systemically characterized. It is found that the high calcination temperature destroys the hexagonal nanoplate morphology and leads to decreased surface areas and pore volumes. In addition, the activity of Co3O4 nanoplates toward the ORR and OER and the capacitance values decrease with an increase of the calcination temperature. From the ORR/OER activity and the specific capacitance normalized by the specific and electrochemical surface area, the intrinsic electrochemical performance may be correlated to the surface oxidation states of Co and O. The high calcination temperature leads to the high amounts of adsorbed oxygen species and Co3+ atoms on the surface, which may be the key for the high intrinsic ORR and OER activity based on the electrochemical surface area. However, the apparent performance is insufficient due to the greatly reduced surface area. For the pseudocapacitive performance, on the contrary, the greater amount of Co2+ on the surface is favorable. Hence, the inconsistent electrochemical performance of Co3O4 may originate from different geometries and surface oxidation states on the surface, which are affected by the calcination temperature in the synthesis process. This work provides insights into the design and optimization of non-precious materials in electrochemical systems, and offers a feasible strategy to improve the performance by using a low-temperature calcination method.