Enhancing photocatalytic oxygen evolution activity of cobalt-based spinel nanoparticles

Photocatalytic water oxidation is one of the critical reactions for solar fuel production from abundant sources. Among all the metal oxides, Co ₃O₄ spinel exhibits a high activity as an oxygen evolution catalyst. In this paper, we demonstrate that the photocatalytic oxygen evolution activity of Co₃O₄ spinel can be further enhanced by substituting cobalt with manganese in the spinel structure. Using a facile hydrothermal approach, we have successfully synthesized pure, Mn-substituted, and Ni-substituted Co₃O₄ nanoparticles with a typical particle size of 5-7 nm. The morphologies and crystal structures of the as-synthesized nanoparticle catalysts have been carefully examined using various structural characterization techniques, including PXRD, TEM, gas adsorption, and XAS. The photocatalytic activities of as-made nanoparticles have been investigated using a well-studied visible light driven [Ru(bpy) ₃]²⁺-persulfate system. In both Clark electrode and reactor/GC systems, Mn-substituted Co₃O₄ nanoparticles exhibited the highest TOF among all the three catalysts. The data presented in this paper suggest that the photocatalytic water oxidation activity of Co ₃O₄ spinel catalyst could be further enhanced by Mn ^3.1+ substitution at the octahedral sites.