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

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 (-CoO NPs), which enables over 40 times higher mass-specific activity toward HO 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 -CoO NPs. Moreover, the five-coordinate Al (Al) sites produced by the dehydration of kaolinite are indispensable for forming the epitaxial interface. Theoretical calculations reveal that the local electron densities around Al sites are lower than those of general six-coordinate Al sites, which render Al sites with strong adsorption capability that facilitates the nucleation of -CoO NPs. Also, the Al sites induce the electron transfer from -CoO to the kaolinite support that results in the upshift of the Co 3d band center and hence improve the HO 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.