A Simple and Scalable Route to Synthesize Co<i>_x</i>Cu₁₋<i>_x</i>Co₂O₄@Co<i>_y</i>Cu₁₋<i>_y</i>Co₂O₄ Yolk–Shell Microspheres, A High‐Performance Catalyst to Hydrolyze Ammonia Borane for Hydrogen Production

Abstract

Yolk-shell structured micro/nano-sized materials have broad and important applications in different areas due to their unique spatial configurations. In this study, yolk-shell structured Co₃ O₄ @Co₃ O₄ is prepared using a simple and scalable hydrothermal reaction, followed by a calcination process. Then, Co_x Cu_1- _x Co₂ O₄ @Co_y Cu_1- _y Co₂ O₄ microspheres are synthesized via adsorption and calcination processes using the as-prepared Co₃ O₄ @Co₃ O₄ as the precursor. A possible formation mechanism of the yolk-shell structures is proposed based on the characterization results, which is different from those of yolk-shell structures in previous study. For the first time, the catalytic activity of yolk-shell structured catalysts in ammonia borane (AB) hydrolysis is studied. It is discovered that the yolk-shell structured Co_x Cu_1- _x Co₂ O₄ @Co_y Cu_1- _y Co₂ O₄ microspheres exhibit high performance with a turnover frequency (TOF) of 81.8 mol_hydrogen min^-1 mol_cat ^-1 . This is one of the highest TOF values reported for a noble-metal-free catalyst in the literature. Additionally, the yolk-shell structured Co_x Cu_1- _x Co₂ O₄ @Co_y Cu_1- _y Co₂ O₄ microspheres are highly stable and reusable. These yolk-shell structured Co_x Cu_1- _x Co₂ O₄ @Co_y Cu_1- _y Co₂ O₄ microsphere is a promising catalyst candidate in AB hydrolysis considering the excellent catalytic behavior and low cost.