19. Hollow-Structured Layered Double Hydroxide: Structure Evolution Induced by Gradient Composition

Zhou, D., Zhang, Q., Wang, S., Jia, Y., Liu, W., Duan, H.*, Sun, X.
Inorg Chem 2020, 59, 1804-1809.
DOI: 10.1021/acs.inorgchem.9b03005

Abstract
The rational design of hollow-structured materials with high specific area, advanced mass transfer, and exposure of selected sites is of great significance in both fundamental scientific research and applicable industrialization fields. In this work, we report a CoAl layered double hydroxides (LDH) nanoring evolved from integrate nanosheet in a urea hydrolysis process, showing enhanced oxygen reduction reaction activity. Detailed investigations into the evolution nature suggest that a gradient-increased Al³⁺ composition exists in the core region of the nanosheet arised from distinctly lower solubility of Al³⁺ than Co²⁺ in the synthesis; therefore, the selective etching of Al³⁺ by OH^– produced from urea hydrolysis leads to the formation of nanoring structure. Probed as an oxygen reduction reaction catalyst, the CoAl-LDH nanoring illustrates a half-wave potential lowered by around 110 mV compared to the integrate nanosheet counterpart, which might be due to the exposure of more edge sites with higher activity. This work paves a novel route for fabricating hollow-structured Al-contained metal hydroxides with defined outer edge and inner voids for multiple purposes.