General synthesis of CoCeMO trimetallic oxides via a cation exchange reaction for the oxygen evolution reaction

Cobalt-based spinel oxides are considered potential candidates for the oxygen evolution reaction (OER) due to their abundant valence changes and promising electrochemical activity, but their low intrinsic activity hinders their practical applications. Herein, we synthesize a series of CoCeMO (M = Zn, Ni, Ru, Er, Mg, Mn, Sn) derived from CoCeM coordination-driven self-assembled aggregates (CDSAAs) using a general ion exchange and subsequent calcination method. Interestingly, CoCeMO exhibit different morphologies from porous nanospheres, particle-stacked nanospheres, to hollow nanospheres as the third metal element is altered. Markedly, CoCeZnO porous nanospheres (PNs) exhibit the best OER performance. The XPS results reveal that the existence of CeO₂ and Zn²⁺ ions significantly increased the Co²⁺/Co³⁺ ratio and the content of oxygen vacancies in Co₃O₄. Furthermore, Co²⁺ can be used as highly reactive sites to form CoOOH and the high content of oxygen vacancies can optimize the oxygen-containing intermediate adsorption energy, both of which can effectively improve the OER performance. Therefore, well-designed CoCeZnO PNs demonstrate high OER activity with a lower overpotential (η = 333 mV) than that of commercial RuO₂ (344 mV) in 10 mA cm^-2, a Tafel slope of 98 mV dec^-1, and a long-term durability of 45 h. This work may provide some inspiration for the design of trimetallic oxide nanomaterials.