Mineral-Mediated\nEpitaxial Growth of CoO Nanoparticles\nfor Efficient Electrochemical H<sub>2</sub>O<sub>2</sub> Activation

Solution-phase epitaxy is a versatile method to synthesize\nfunctional\nnanomaterials with customized properties, where supports play a central\nrole as they not only serve as nucleation templates but also greatly\naffect the local electronic structures. However, developing functional\nsupports remains a great challenge. Herein, inspired by the commonly\nobserved epitaxy of minerals in the natural environment, we report\nusing calcination-modified kaolinite as the support for the epitaxial\ngrowth of hexagonal CoO nanoparticles (<i>h</i>-CoO NPs),\nwhich enables over 40 times higher mass-specific activity toward H<sub>2</sub>O<sub>2</sub> electrochemical activation than the counterpart\nwithout the support. High-resolution electron microscopy, magic-angle\nspinning nuclear magnetic resonance, and X-ray absorption fine structure\nresults prove that the Al sites in kaolinite play a crucial role in\nthe formation of <i>h</i>-CoO NPs. Moreover, the five-coordinate\nAl (Al<sup>V</sup>) sites produced by the dehydration of kaolinite\nare indispensable for forming the epitaxial interface. Theoretical\ncalculations reveal that the local electron densities around Al<sup>V</sup> sites are lower than those of general six-coordinate Al sites,\nwhich render Al<sup>V</sup> sites with strong adsorption capability\nthat facilitates the nucleation of <i>h</i>-CoO NPs. Also,\nthe Al<sup>V</sup> sites induce the electron transfer from <i>h</i>-CoO to the kaolinite support that results in the upshift\nof the Co 3d band center and hence improve the H<sub>2</sub>O<sub>2</sub> activation kinetics. Our results demonstrate the superiority\nof nanoclay as functional supports and could offer a more benign strategy\nto the solution-phase epitaxy production of functional nanomaterials\nfor diverse applications.