Mineral-Mediated Epitaxial Growth of CoO Nanoparticles for Efficient Electrochemical H₂O₂ Activation.

Abstract

Solution-phase epitaxy is a versatile method to synthesize functional nanomaterials with customized properties, where supports play a central role as they not only serve as nucleation templates but also greatly affect the local electronic structures. However, developing functional supports remains a great challenge. Herein, inspired by the commonly observed epitaxy of minerals in the natural environment, we report using calcination-modified kaolinite as the support for the epitaxial growth of hexagonal CoO nanoparticles (<i>h</i>-CoO NPs), which enables over 40 times higher mass-specific activity toward H₂O₂ electrochemical activation than the counterpart without the support. High-resolution electron microscopy, magic-angle spinning nuclear magnetic resonance, and X-ray absorption fine structure results prove that the Al sites in kaolinite play a crucial role in the formation of <i>h</i>-CoO NPs. Moreover, the five-coordinate Al (Al^V) sites produced by the dehydration of kaolinite are indispensable for forming the epitaxial interface. Theoretical calculations reveal that the local electron densities around Al^V sites are lower than those of general six-coordinate Al sites, which render Al^V sites with strong adsorption capability that facilitates the nucleation of <i>h</i>-CoO NPs. Also, the Al^V sites induce the electron transfer from <i>h</i>-CoO to the kaolinite support that results in the upshift of the Co 3d band center and hence improve the H₂O₂ activation kinetics. Our results demonstrate the superiority of nanoclay as functional supports and could offer a more benign strategy to the solution-phase epitaxy production of functional nanomaterials for diverse applications.